Vitamins

Objectives:

1. Describe adequate intake of all Vitamins.

2. Identify the function of Vitamins in the development of healty bones and tissues.

Vitamin A and Carotenoids

 Vitamin A: What is it?


Vitamin A is a family of fat-soluble vitamins. Retinol is one of the most active, or usable, forms of vitamin A, and is found in animal foods such as liver and eggs and in some fortified food products. Retinol is often called preformed vitamin A. It can be converted to retinal and retinoic acid, other active forms of the vitamin A family.

Some plant foods contain darkly colored pigments called provitamin A carotenoids that can be converted to vitamin A. In the U.S., approximately 26% and 34% of vitamin A consumed by men and women is provided by provitamin A carotenoids.  Beta-carotene is a provitamin A carotenoid that is more efficiently converted to retinol than other carotenoids. For example, alpha-carotene and b-cryptoxanthin are also converted to vitamin A, but only half as efficiently as beta-carotene  Lycopene, lutein, and zeaxanthin are other carotenoids commonly found in food. They are not sources of vitamin A but may have other health promoting properties. The Institute of Medicine (IOM) encourages consumption of carotenoid-rich fruits and vegetables for their health-promoting benefits.

Vitamin A plays an important role in vision, bone growth, reproduction, cell division and cell differentiation, which is the process by which a cell decides what it is going to become.

It helps maintain the surface linings of the eyes and the respiratory, urinary, and intestinal tracts. When those linings break down, bacteria can enter the body and cause infection. Vitamin A also helps maintain the integrity of skin and mucous membranes that function as a barrier to bacteria and viruses.  Vitamin A helps regulate the immune system. The immune system helps prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses. Vitamin A may help lymphocytes, a type of white blood cell that fights infections, function more effectively.

Some carotenoids, in addition to serving as a source of vitamin A, have been shown to function as antioxidants in laboratory tests. However, this role has not been consistently demonstrated in humans. Antioxidants protect cells from free radicals, which are potentially damaging by-products of oxygen metabolism that may contribute to the development of some chronic diseases.

What foods provide vitamin A?

Preformed vitamin A is found in animal foods such as whole eggs, whole milk and liver.  
Most fat free milk and dried nonfat milk solids sold in the US are fortified with vitamin A to replace the vitamin A lost when the fat is removed. Fortified foods such as fortified breakfast cereals also provide vitamin A. Provitamin A carotenoids are abundant in darkly colored fruits and vegetables. Tables 4 and 5 at the end of this document list animal sources of vitamin A and a variety of plant sources of provitamin A carotenoids.  It is important for you to regularly eat foods that provide vitamin A or beta-carotene even though vitamin A is stored in the liver. Stored vitamin A will help meet needs when intake of provitamin A carotenoids or preformed vitamin A is low.

 What is the Recommended Dietary Allowance for vitamin A for children and adults?

Dietary Reference Intakes (DRIs) is the umbrella term for a group of reference values used for planning and assessing diets for healthy people.

One of those references values, the Recommended Dietary Allowance (RDA), is the average daily dietary intake level sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each age and gender group.

RDAs for vitamin A are listed as Retinol Activity Equivalents (RAE) to account for the different activities of retinol and provitamin A carotenoids. In the table below, RDAs are also listed in International Units (IU) because food and some supplement labels list vitamin A content in International Units (1 RAE in micrograms (ug) = 3.3 IU). The 2001 RDAs for adults and children in ug RAE and IUs are:

 Table 1: Recommended Dietary Allowances for vitamin A in micrograms (ug) Retinol Activity Equivalents (RAE) and International Units (IUs) for children and adults.

Age (years)

Children

Men

 Women

 Pregnancy

 Lactation

1-3

300 ug or 1000 IU

 

 

 

 

4-8

400 ug or 1333 IU

 

 

 

 

9-13

600 ug or 2000 IU

 

x

x

x

14-18

 

900 ug or
3000 IU

700 ug or
2330 IU

750 ug or
2500 IU

1200 ug or
4000 IU

19 +

 

900 ug or
3000 IU

700 ug or
2330 IU

770 ug or
2565 IU

1300 ug or
4335 IU

Table 2: Adequate Intake for vitamin A in micrograms (ug) and International Units (IU) for infants

There is insufficient information to establish a RDA for vitamin A for infants. An adequate intake (AI) has been established that is based on the amount of vitamin A consumed by healthy infants who are fed breast milk.

Age (months)

Males and Females

0 to 6

400 ug or 1330 IU

7 to 12

500 ug or 1665 IU

Results of two national surveys, the third National Health and Nutrition Examination Survey (NHANES III 1988-91) and the Continuing Survey of Food Intakes by Individuals (CSFII 1994) suggested that dietary intakes of some Americans do not meet recommended levels for vitamin A. These surveys highlight the importance of encouraging all Americans to include dietary sources of vitamin A in their daily diets.  There is no RDA for beta-carotene or other provitamin A carotenoids. The Institute of Medicine report suggests that consuming 3 to 6 mg of beta-carotene daily will maintain plasma beta-carotene blood levels in the range associated with a lower risk of chronic diseases. A diet that provides five or more servings of fruits and vegetables per day and includes some dark green and leafy vegetables and deep yellow or orange fruits should provide recommended amounts of beta-carotene

When can vitamin A deficiency occur?

Vitamin A deficiency rarely occurs in the United States, but it is still a major public health problem in the developing world.  At least 3 million children develop xeropthalmia, damage to the cornea of the eye, and 250,000 to 500,000 go blind each year from a deficiency of vitamin A. Most of these children live in developing countries. Night blindness is one of the first signs of vitamin A deficiency. In ancient Egypt it was known that night blindness could be cured by eating liver, which was later found to be a rich source of vitamin A. Vitamin A deficiency contributes to blindness by making the cornea very dry and promoting damage to the retina and cornea.

Vitamin A deficiency diminishes the ability to fight infections.

In countries where immunization programs are not widespread and vitamin A deficiency is common, millions of children die each year from complications of infectious diseases such as measles. When there is not enough vitamin A, cells lining the lung lose their ability to remove disease-causing microorganisms. This may contribute to the pneumonia associated with vitamin A deficiency.  There is increased interest in subclinical forms of vitamin A deficiency, described as low storage levels of vitamin A that do not cause overt deficiency symptoms. This mild degree of vitamin A deficiency may increase children’s risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness. Children living in the United States who are considered to be at increased risk for subclinical vitamin A deficiency include:

  • toddlers and preschool age children,
  • children living at or below the poverty level,
  • children with inadequate health care or immunizations,
  • children living in areas with known nutritional deficiencies,
  • recent immigrants or refugees from developing countries with high incidence of vitamin A deficiency or measles, and
  • children with diseases of the pancreas, liver, intestines, or with inadequate fat digestion/absorption

Vitamin A deficiency can occur when vitamin A is lost through chronic diarrhea, and through an overall inadequate intake, as is often seen with protein-calorie malnutrition.

Low plasma retinol concentrations indicate depleted levels of vitamin A. This occurs with vitamin A deficiency but also can result from an inadequate intake of protein, calories and zinc. These nutrients are needed to make Retinol Binding Protein (RBP), which is essential for mobilizing vitamin A from your liver and transporting vitamin A to your general circulation.  Iron deficiency can also limit the metabolism of vitamin A, and iron supplements provided to iron deficient individuals may improve vitamin A nutriture as well as iron status.

Excess alcohol intake depletes vitamin A stores. Also, diets high in alcohol usually do not provide recommended amounts of vitamin A. It is very important for anyone who consumes excessive amounts of alcohol to include good sources of vitamin A in his or her diet. However, Vitamin A supplementation may not be recommended for individuals who abuse alcohol because alcohol may increase liver toxicity associated with excess intakes of vitamin A. A medical doctor would need to evaluate this situation and determine the need for vitamin A supplementation.

Fat malabsorption can promote diarrhea and prevent normal absorption of vitamin A.

This is most often seen with cystic fibrosis, sprue, pancreatic disorders, and after stomach surgery. Healthy adults usually have a reserve of vitamin A stored in their livers and should not be at risk of deficiency during periods of temporary or short term fat malabsorption. Long-term problems absorbing fat, however, may result in deficiency, and in these instances physicians may advise vitamin A supplementation.

Vegetarians who do not consume eggs and dairy foods need greater amounts of provitamin A carotenoids to meet their need for vitamin A.

It is important for vegetarians to include a minimum of five servings of fruits and vegetables daily and to regularly choose dark green leafy vegetables and orange and yellow fruits to consume recommended amounts of vitamin A.

What is the association between vitamin A, beta carotene and cancer?
Surveys suggest an association between diets rich in beta-carotene and vitamin A and a lower risk of some types of cancer.  
There is evidence that a higher intake of green and yellow vegetables or other food sources of beta-carotene and/or vitamin A may decrease the risk of lung cancer. However, a number of studies that tested the role of beta-carotene supplements in cancer prevention did not find it to be protective. In a study of 29,000 men, incidence of lung cancer was greater in the group of smokers who took a daily supplement of beta-carotene .

The Carotene and Retinol Efficacy Trial, a lung cancer chemoprevention trial that provided randomized subjects with supplements of beta-carotene and vitamin A, was stopped after researchers discovered that subjects receiving beta-carotene had a 46% higher risk of dying from lung cancer than those who did not receive beta-carotene . The Institute of Medicine (IOM) states that “beta-carotene supplements are not advisable for the general population,” although they also state that this advice “does not pertain to the possible use of supplemental beta-carotene as a provitamin A source for the prevention of vitamin A deficiency in populations with inadequate vitamin A nutriture” .

 Can an excess intake of vitamin A promote osteoporosis?

Osteoporosis, a disorder characterized by porous, weak bones, is a serious public health problem for more than 10 million Americans, 80% of whom are women. Another 18 million Americans have decreased bone density, which precedes the development of osteoporosis. Researchers have identified many factors that increase the risk for developing osteoporosis, including being female, thin, inactive, at advanced age, and having a family history of osteoporosis. An inadequate dietary intake of calcium, cigarette smoking and excessive intake of alcohol also increase the risk of developing osteoporosis.

Researchers are now examining a potential new risk factor for osteoporosis: an excess intake of vitamin A.

Animal, human, and laboratory research suggest an association between greater vitamin A intake and weaker bones. Researchers have also noticed that worldwide, the highest incidence of osteoporosis occurs in northern Europe, a population with a high intake of vitamin A. However, decreased biosynthesis of vitamin D associated with lower levels of sun exposure in this population may also contribute to this finding.

This issue was also examined by researchers with the Nurses Health Study, who looked at the association between vitamin A intake and hip fractures in over 72,000 postmenopausal women.

In this study, women who consumed the most vitamin A in foods and supplements (greater than or equal to 3000 mcg per day as retinol equivalents, which is over three times the recommended intake for adult men and women) had a significantly increased risk of experiencing a hip fracture as compared to those consuming the least amount. (less than 1250 mcg per day of retinol equivalents). The effect was lessened by use of estrogens but still raises questions about the effects of a high intake of vitamin A. In particular this raises questions about the effect of preformed vitamin A or retinol because retinol intake greater than 2000 mcg per day was associated with an increased risk of hip fracture as compared to a retinol intake less than 500 mcg .

There is no evidence of an association between beta-carotene intake, especially from fruits and vegetables (many of which are naturally high in beta-carotene), and increased risk of osteoporosis.

What is the health risk of too much vitamin A?

Hypervitaminosis A refers to high storage levels of vitamin A in the body that can lead to toxic symptoms. There are three major adverse effects of hypervitaminosis A:

  •     birth defects,
  •     liver abnormalities,
  •     reduced bone mineral density that may result in osteoporosis 

 Toxic symptoms can also arise after consuming very large amounts of preformed vitamin A over a short period of time.

Signs of acute toxicity include nausea and vomiting, headache, dizziness, blurred vision, and muscular uncoordination.  Although hypervitaminosis A can occur when very large amounts of liver are regularly consumed, most cases of vitamin A toxicity result from an excess intake of vitamin A in supplements.  The Institute of Medicine has established Daily Tolerable Upper Levels (UL) of intake for vitamin A from supplements that apply to healthy populations. The UL was established to help prevent the risk of vitamin A toxicity. The risk of adverse health effects increases at intakes greater than the UL. The UL does not apply to malnourished individuals receiving vitamin A either periodically or through fortification programs as a means of preventing deficiency. It also does not apply to individuals being treated with vitamin A by medical doctors for diseases such as retinitis pigmentosa.

 Table 3: Tolerable Upper Intake Levels (UL) for preformed vitamin A in micrograms (ug) and International Units (IU)
for infants, children, and adults (1)

Age

Children

Men

 Women

 Pregnancy

 Lactation

0-12 months

600 ug or 2000 IU

 

 

 

 

1-3 years

600 ug or 2000 IU

 

 

 

 

4-8 years

900 ug or 3000 IU

 

x

x

x

9-13 years

1700 ug or 5665 IU

 

 

 

 

14-18 years

 

2800 ug or
9335 IU

2800 ug or
9335 IU

2800 ug or
9335 IU

2800 ug or
9335 IU

19+ years

 

3000 ug or
10,000 IU

3000 ug or
10,000 IU

3000 ug or
10,000 IU

3000 ug or
10,000 IU

Retinoids are compounds that are chemically similar to vitamin A.

Over the past 15 years, synthetic retinoids have been prescribed for acne, psoriasis, and other skin disorders. Isotretinoin (Roaccutane® or Accutane®) is considered an effective anti-acne therapy.  At very high doses, however, it can be toxic, which is why this medication is usually saved for the most severe forms of acne. The most serious consequence of this medication is birth defects. It is extremely important for sexually active females who may become pregnant and who take these medications to use an effective method of birth control. Women of childbearing age who take these medications are advised to undergo monthly pregnancy tests to make sure they are not pregnant.

What is the health risk of too many carotenoids?

Nutrient toxicity traditionally refers to adverse health effects from a high intake of a particular vitamin or mineral. For example, large amounts of active, or preformed, vitamin A (naturally found in animal foods such as liver but also available in dietary supplements) can cause birth defects.

Selected Food Sources of Vitamin A

As the 2000 Dietary Guidelines for Americans state, “Different foods contain different nutrients. No single food can supply all the nutrients in the amounts you need”. The following tables list a variety of dietary sources of vitamin A and provitamin A carotenoids.  As the tables show, liver, eggs and whole milk are good animal sources of vitamin A. Many orange fruits and green vegetables are good sources of provitamin A carotenoids. In addition, food manufacturers fortify a wide range of products with vitamin A. Breakfast cereals, pastries, breads, crackers, cereal grain bars and other foods may be fortified with 10% to 15% of the Daily Value (DV) for vitamin A.

 Table 4: Selected Animal Sources of Vitamin A 

Animal sources of vitamin A provide the best aborbed form of this vitamin.

 Food

IU/
International
Units

%DV *

Liver, beef, cooked, 3 oz

30,325

610

Liver, chicken, cooked, 3 oz

13,920

280

Egg substitute, fortified, 1/4 cup

1355

25

Fat free milk, fortified with vitamin A, 1 cup

500

10

Cheese pizza, 1/8 of a 12" diameter pie

380

8

Milk, whole, 3.25% fat, 1 cup

305

6

Cheddar cheese, 1 ounce

300

6

Whole egg, 1 medium

280

6

% DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for vitamin A is 5,000 IU (1,500 micrograms retinol). Most food labels do not list a food’s vitamin A content. The percent DV (%DV) listed on the table above indicates the percentage of the DV provided in one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet.

Table 5: Selected Plant Sources of Vitamin A (from beta-carotene) (18

Plant sources of beta-carotene are not as well absorbed as animal sources of vitamin A, especially when they are consumed whole and raw. However, they are still a valuable source of this vitamin.

 Food

IU/ International Units

%DV *

Carrot, 1 raw (7 1/2 inches long)

20,250

410

Carrots, boiled, 1/2 cup slices

19,150

380

Carrot juice, canned, 1/2 cup

12,915

260

Sweet potatoes, canned , drained solids, 1/2 cup

7,015

140

Spinach, frozen, boiled, 1/2 cup

7,395

150

Mango, raw, 1 cup sliced

6,425

130

Vegetable soup, canned, chunky, ready-to-serve, 1 cup

5,880

115

Cantaloupe, raw, 1 cup

5,160

100

Kale, frozen, boiled, 1/2 cup

4,130

80

Spinach, raw, 1 cup

2,015

40

Apricot nectar, canned, 1/2 cup

1,650

35

Oatmeal, instant, fortified, plain, prepared with water, 1 packet

1,510

30

Tomato juice, canned, 6 ounces

1,010

20

Apricots, with skin, juice pack, 2 halves

610

10

Pepper, sweet, red, raw, 1 ring, 3 inches in diameter by 1/4-inch thick

570

10

Peas, frozen, boiled, 1/2 cup

535

10

Peach, raw, 1 medium

525

10

Peaches, canned, water pack, 1/2 cup halves or slices

470

10

Papaya, raw, 1 cup cubes

400

8

*DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for vitamin A is 5,000 IU (1,500 micrograms retinol). Most food labels do not list a food’s vitamin A content. The percent DV (%DV) listed on the table above indicates the percentage of the DV provided in one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet.

Vitamin B6

Vitamin B6: What is it ?

Vitamin B6 is a water-soluble vitamin that exists in three major chemical forms: pyridoxine, pyridoxal, and pyridoxamine. It performs a wide variety of functions in te body and is essential for your good health. For example, vitamin B6 is needed for more than 100 enzymes involved in protein metabolism. It is also essential for red blood cell metabolism. The nervous and immune systems need vitamin B6 to function efficiently, and it is also needed for the conversion of tryptophan (an amino acid) to niacin (a vitamin).

Hemoglobin within red blood cells carries oxygen to tissues. Your body needs vitamin B6 to make hemoglobin. Vitamin B6 also helps increase the amount of oxygen carried by hemoglobin. A vitamin B6 deficiency can result in a form of anemia that is similar to iron deficiency anemia.  An immune response is a broad term that describes a variety of biochemical changes that occur in an effort to fight off infections. Calories, protein, vitamins, and minerals are important to your immune defenses because they promote the growth of white blood cells that directly fight infections. Vitamin B6, through its involvement in protein metabolism and cellular growth, is important to the immune system. It helps maintain the health of lymphoid organs (thymus, spleen, and lymph nodes) that make your white blood cells. Animal studies show that a vitamin B6 deficiency can decrease your antibody production and suppress your immune response.

Vitamin B6 also helps maintain your blood glucose (sugar) within a normal range. When caloric intake is low your body needs vitamin B6 to help convert stored carbohydrate or other nutrients to glucose to maintain normal blood sugar levels. While a shortage of vitamin B6 will limit these functions, supplements of this vitamin do not enhance them in well-nourished individuals.

What foods provide vitamin B6 ?

Vitamin B6 is found in a wide variety of foods including fortified cereals, beans, meat, poultry, fish, and some fruits and vegetables. The table of selected food sources of vitamin B6 suggests many dietary sources of B6.

What is the Recommended Dietary Allowance for vitamin B6 for adults?The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97 to 98 percent) healthy individuals in each life-stage and gender group.The 1998 RDAs for vitamin B6 (12) for adults, in milligrams, are:

Life-Stage

 Men

 Women

 Pregnancy

 Lactation

Ages 19-50

1.3 mg

1.3 mg

 

 

Ages 51+

1.7 mg

1.5 mg

 

 

All ages

 

 

1.9 mg

2.0 mg

Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III1988-94) (12, 13) and the Continuing Survey of Food Intakes by Individuals (1994-96 CSFII), indicated that diets of most Americans meet current intake recommendations for vitamin B6.

When can a vitamin B6 deficiency occur?

Clinical signs of vitamin B6 deficiency are rarely seen in the United States. Many older Americans, however, have low blood levels of vitamin B6, which may suggest a marginal or sub-optimal vitamin B6 nutritional status. Vitamin B6 deficiency can occur in individuals with poor quality diets that are deficient in many nutrients. Symptoms occur during later stages of deficiency, when intake has been very low for an extended time. Signs of vitamin B6 deficiency include dermatitis (skin inflammation), glossitis (a sore tongue), depression, confusion, and convulsions. Vitamin B6 deficiency also can cause anemia. Some of these symptoms can also result from a variety of medical conditions other than vitamin B6 deficiency. It is important to have a physician evaluate these symptoms so that appropriate medical care can be given.

 Who may need extra vitamin B6 to prevent a deficiency?

Individuals with a poor quality diet or an inadequate B6 intake for an extended period may benefit from taking a vitamin B6 supplement if they are unable to increase their dietary intake of vitamin B6 . Alcoholics and older adults are more likely to have inadequate vitamin B6 intakes than other segments of the population because they may have limited variety in their diet. Alcohol also promotes the destruction and loss of vitamin B6 from the body. Asthmatic children treated with the medicine theophylline may need to take a vitamin B6 supplement. Theophylline decreases body stores of vitamin B6, and theophylline-induced seizures have been linked to low body stores of the vitamin. A physician should be consulted about the need for a vitamin B6 supplement when theophylline is prescribed.

 What are some current issues and controversies about vitamin B6?

 Vitamin B6 and the nervous system

 Vitamin B6 is needed for the synthesis of neurotransmitters such as serotonin and dopamine. These neurotransmitters are required for normal nerve cell communication. Researchers have been investigating the relationship between vitamin B6 status and a wide variety of neurologic conditions such as seizures, chronic pain, depression, headache, and Parkinson's disease.  Lower levels of serotonin have been found in individuals suffering from depression and migraine headaches. So far, however, vitamin B6 supplements have not proved effective for relieving these symptoms. One study found that a sugar pill was just as likely as vitamin B6 to relieve headaches and depression associated with low dose oral contraceptives.

Alcohol abuse can result in neuropathy, abnormal nerve sensations in the arms and legs. A poor dietary intake contributes to this neuropathy and dietary supplements that include vitamin B6 may prevent or decrease its incidence.

Vitamin B6 and carpal tunnel syndrome

Vitamin B6 was first recommended for carpal tunnel syndrome almost 30 years ago. Several popular books still recommend taking 100 to 200 milligrams (mg) of vitamin B6 daily to treat carpal tunnel syndrome, even though scientific studies do not indicate it is effective. Anyone taking large doses of vitamin B6 supplements for carpal tunnel syndrome needs to be aware that the Institute of Medicine recently established an upper tolerable limit of 100 mg per day for adults. There are documented cases in the literature of neuropathy caused by excessive vitamin B6 taken for treatment of carpal tunnel syndrome.

Vitamin B6 and premenstrual syndrome

Vitamin B6 has become a popular remedy for treating the discomforts associated with premenstrual syndrome (PMS). Unfortunately, clinical trials have failed to support any significant benefit. One recent study indicated that a sugar pill was as likely to relieve symptoms of PMS as vitamin B6. In addition, vitamin B6 toxicity has been seen in increasing numbers of women taking vitamin B6 supplements for PMS. One review indicated that neuropathy was present in 23 of 58 women taking daily vitamin B6 supplements for PMS whose blood levels of B6 were above normal. There is no convincing scientific evidence to support recommending vitamin B6 supplements for PMS.

Vitamin B6 and interactions with medications

There are many drugs that interfere with the metabolism of vitamin B6. Isoniazid, which is used to treat tuberculosis, and L-DOPA, which is used to treat a variety of neurologic problems such as Parkinson's disease, alter the activity of vitamin B6. There is disagreement about the need for routine vitamin B6 supplementation when taking isoniazid. Acute isoniazid toxicity can result in coma and seizures that are reversed by vitamin B6, but in a group of children receiving isoniazid, no cases of neurological or neuropsychiatric problems were observed regardless of whether or not they took a vitamin B6 supplement. Some doctors recommend taking a supplement that provides 100% of the RDA for B6 when isoniazid is prescribed, which is usually enough to prevent symptoms of vitamin B6 deficiency. It is important to consult with a physician about the need for a vitamin B6 supplement when taking isoniazid.

What is the relationship between vitamin B6, homocysteine, and heart disease?

A deficiency of vitamin B6, folic acid, or vitamin B12 may increase your level of homocysteine, an amino acid normally found in your blood. There is evidence that an elevated homocysteine level is an independent risk factor for heart disease and stroke. The evidence suggests that high levels of homocysteine may damage coronary arteries or make it easier for blood clotting cells called platelets to clump together and form a clot. However, there is currently no evidence available to suggest that lowering homocysteine level with vitamins will reduce your risk of heart disease. Clinical intervention trials are needed to determine whether supplementation with vitamin B6, folic acid, or vitamin B12 can help protect you against developing coronary heart disease.

What is the health risk of too much vitamin B6 ?

Too much vitamin B6 can result in nerve damage to the arms and legs. This neuropathy is usually related to high intake of vitamin B6 from supplements, and is reversible when supplementation is stopped. According to the Institute of Medicine, "Several reports show sensory neuropathy at doses lower than 500 mg per day". As previously mentioned, the Food and Nutrition Board of the Institute of Medicine has established an upper tolerable intake level (UL) for vitamin B6 of 100 mg per day for all adults "As intake increases above the UL, the risk of adverse effects increases."

Selected Food Sources of vitamin B6

 As the 2000 Dietary Guidelines for Americans state, "Different foods contain different nutrients and other healthful substances. No single food can supply all the nutrients in the amounts you need". As the following table indicates, vitamin B6 is found in a wide variety of foods. Foods such as fortified breakfast cereals, fish including salmon and tuna fish, meats such as pork and chicken, bananas, beans and peanut butter, and many vegetables will contribute to your vitamin B6 intake.

 Table of Food Sources of Vitamin B6

 Food

 

Milligrams

 

%DV*

Ready-to-eat cereal, 100% fortified, 3/4 c

2.00

100

Potato, Baked, flesh and skin, 1 medium

0.70

35

Banana, raw, 1 medium

0.68

34

Garbanzo beans, canned, 1/2 c

0.57

30

Chicken breast, meat only, cooked, 1/2 breast

0.52

25

Ready-to-eat cereal, 25% fortified, 3/4 c

0.50

25

Oatmeal, instant, fortified, 1 packet

0.42

20

Pork loin, lean only, cooked, 3 oz

0.42

20

Roast beef, eye of round, lean only, cooked, 3 oz

0.32

15

Trout, rainbow, cooked, 3 oz

0.29

15

Sunflower seeds, kernels, dry roasted, 1 oz

0.23

10

Spinach, frozen, cooked, 1/2 c

0.14

8

Tomato juice, canned, 6 oz

0.20

10

Avocado, raw, sliced, 1/2 cup

0.20

10

Salmon, Sockeye, cooked, 3 oz

0.19

10

Tuna, canned in water, drained solids, 3 oz

0.18

10

Wheat bran, crude or unprocessed, 1/4 c

0.18

10

Peanut butter, smooth, 2 Tbs.

0.15

8

Walnuts, English/Persian, 1 oz

0.15

8

Soybeans, green, boiled, drained, 1/2 c

0.05

2

Lima beans, frozen, cooked, drained, 1/2 c

0.10

6

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for vitamin B6 is 2.0 milligrams (mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells you what percentage of the DV is provided in one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet.

Vitamin B12

What is it?

Vitamin B12, also called cobalamin, is important to good health. It helps maintain healthy nerve cells and red blood cells, and is also needed to make DNA, the genetic material in all cells. Vitamin B12 is bound to the protein in food. Hydrochloric acid in the stomach releases B12 from protein during digestion. Once released, B12 combines with a substance called intrinsic factor (IF) before it is absorbed into the bloodstream.

What foods provide vitamin B12?

Vitamin B12 is naturally found in animal foods including fish, milk and milk products, eggs, meat, and poultry. Fortified breakfast cereals are an excellent source of vitamin B12 and a particularly valuable source for vegetarians. The table of selected food sources of vitamin B12 suggests dietary sources of vitamin B12.

 What is the Recommended Dietary Allowance for vitamin B12 for adults?

The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97 to 98 percent) healthy individuals in each life-stage and gender group. The 1998 RDAs for vitamin B12 (in micrograms) for adults are:

Life-Stage

 Men

 Women

 Pregnancy

 Lactation

Ages 19+

2.4 mcg

2.4 mcg

 

 

All ages

 

 

2.6 mcg  

2.8 mcg

Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III-1988-91) (8) and the Continuing Survey of Food Intakes by Individuals (CSFII 1994-96) (7) found that most adult men and women consume recommended amounts of vitamin B12 (6-8).

When is a deficiency of vitamin B12 likely to occur?

Diets of most adult Americans provide recommended intakes of vitamin B12, but deficiency may still occur as a result of an inability to absorb B12 from food. It can also occur in individuals with dietary patterns that exclude animal or fortified foods. As a general rule, most individuals who develop a vitamin B12 deficiency have an underlying stomach or intestinal disorder that limits the absorption of vitamin B12. Sometimes the only symptom of these intestinal disorders is anemia resulting from B12 deficiency.

Characteristic signs of B12 deficiency include fatigue, weakness, nausea, constipation, flatulence (gas), loss of appetite, and weight loss. Deficiency also can lead to neurological changes such as numbness and tingling in the hands and feet. Additional symptoms of B12 deficiency are difficulty in maintaining balance, depression, confusion, poor memory, and soreness of the mouth or tongue. Some of these symptoms can also result from a variety of medical conditions other than vitamin B12 deficiency. It is important to have a physician evaluate these symptoms so that appropriate medical care can be given.

Who may need a vitamin B12 supplement to prevent a deficiency?


Individuals with pernicious anemia

Pernicious anemia is a form of anemia that occurs when there is an absence of intrinsic factor, a substance normally present in the stomach. Vitamin B12 binds with intrinsic factor before it is absorbed and used by your body. An absence of intrinsic factor prevents normal absorption of B12 and results in pernicious anemia.  Anyone with pernicious anemia usually needs intramuscular (IM) injections (shots) of vitamin B12. It is very important to remember that pernicious anemia is a chronic condition that should be monitored by a physician. Anyone with pernicious anemia has to take lifelong supplemental vitamin B12.

Individuals with gastrointestinal disorders:

Individuals with stomach and small intestinal disorders may not absorb enough vitamin B12 from food to maintain healthy body stores. Sprue and celiac disease are intestinal disorders caused by intolerance to protein in wheat and wheat products. Regional enteritis, localized inflammation of the stomach or small intestine, also results in generalized malabsorption of vitamin B12. Excess bacteria in the stomach and small intestine also can decrease vitamin B12 absorption.  Surgical procedures of the gastrointestinal tract such as surgery to remove all or part of the stomach often result in a loss of cells that secrete stomach acid and intrinsic factor. Surgical removal of the distal ileum, a section of the intestines, also can result in the inability to absorb B12. Anyone who has had either of these surgeries usually requires lifelong supplemental B12 to prevent a deficiency.

Older Adults

Vitamin B12 must be separated from protein in food before it can bind with intrinsic factor and be absorbed by your body. Bacterial overgrowth in the stomach and/or atrophic gastritis, an inflammation of the stomach, contribute to vitamin B12 deficiency in adults by limiting secretions of stomach acid needed to separate vitamin B12 from protein in food. Adults 50 years of age and older with these conditions are able to absorb the B12 in fortified foods and dietary supplements. Health care professionals may advise adults over the age of 50 to get their vitamin B12 from a dietary supplement or from foods fortified with vitamin B12 because 10 to 30 percent of older people may be unable to absorb vitamin B12 in food.

Vegetarians

Vegetarians who do not eat meats, fish, eggs, milk or milk products, or B12 fortified foods consume no vitamin B12 and are at high risk of developing a deficiency of vitamin B12. When adults adopt a vegetarian diet, deficiency symptoms can be slow to appear because it usually takes years to deplete normal body stores of B12. However, severe symptoms of B12 deficiency, most often featuring poor neurological development, can show up quickly in children and breast-fed infants of women who follow a strict vegetarian diet.  Fortified cereals are one of the few plant food sources of vitamin B12, and are an important dietary source of B12 for vegetarians who consume no eggs, milk or milk products. Vegetarian adults who do not consume plant foods fortified with vitamin B12 need to consider taking a B12-containing supplement. Vegetarian mothers should consult with a pediatrician regarding appropriate vitamin B12 supplementation for their infants and children.

Caution: Folic acid may mask signs of vitamin B12 deficiency

Folic acid can correct the anemia that is caused by vitamin B12 deficiency. Unfortunately, folic acid will not correct the underlying B12 deficiency. Permanent nerve damage can occur if vitamin B12 deficiency is not treated. Folic acid intake from food and supplements should not exceed 1,000 micrograms (mcg) daily because large amounts of folic acid can hide the damaging effects of vitamin B12 deficiency. Adults older than 50 years are advised to consult with their physician about the advisability of taking folic acid without also taking a vitamin B12 supplement.

What is the relationship between vitamin B12, homocysteine, and heart disease?

A deficiency of vitamin B12, folate, or vitamin B6 may increase your blood level of homocysteine, an amino acid normally found in your blood. There is evidence that an elevated blood level of homocysteine is an independent risk factor for heart disease and stroke. The evidence suggests that high levels of homocysteine may damage coronary arteries or make it easier for blood clotting cells called platelets to clump together and form a clot. However, there is currently no evidence available to suggest that lowering homocysteine level with vitamins will actually reduce your risk of heart disease. Clinical intervention trials are needed to determine whether supplementation with vitamin B12, folic acid, or vitamin B6 can help protect you against developing coronary heart disease.

 What is the health risk of too much vitamin B12?

Vitamin B12 has a very low potential for toxicity. The Institute of Medicine states that "no adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals." The Institute recommends that adults over 50 years of age get most of their vitamin B12 from supplements or fortified food because of the high incidence of impaired absorption of B12 from unfortified foods in this population.

 Selected Food Sources of Vitamin B12

As the 2000 Dietary Guidelines for Americans state, "Different foods contain different nutrients and other healthful substances. No single food can supply all the nutrients in the amounts you need". As the following table indicates, vitamin B12 is found naturally in animal foods. It is also found in fortified foods such as fortified breakfast cereals.

Table of Food Sources of Vitamin B12

 Food

 

 Micrograms

 

%DV*

Beef liver, cooked, 3 oz

60.0

1000

Fortified breakfast cereals, (100%) fortified),
3/4 c

6.0

100

Trout, rainbow, cooked, 3 oz

5.3

90

Salmon, sockeye, cooked, 3 oz

4.9

80

Beef, cooked, 3 oz

2.1

35

Fortified breakfast cereals (25% fortified),
3/4 c

1.5

25

Haddock, cooked, 3 oz

1.2

20

Clams, breaded and fried, 3/4 c

1.1

20

Oysters, breaded and fried, 6 pieces

1.0

15

Tuna, white, canned in water, 3 oz

0.9

15

Milk, 1 cup

0.9

15

Yogurt, 8 oz

0.9

15

Pork, cooked, 3 oz

0.6

10

Egg, 1 large

0.5

8

American Cheese, 1 oz

0.4

6

Chicken, cooked, 3 oz

0.3

6

Cheddar cheese, 1 oz

0.2

4

Mozzarella cheese, 1 oz

0.2

4

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for vitamin B12 is 6.0 micrograms (mcg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet.

Vitamin C

Here's what you need to know about vitamin C (ascorbic acid) — how much you need, what it does for your body, good food sources, cautions and side effects.

Recommended Dietary Allowance (RDA) for Adults

Life stage

Men

Women

Pregnant

Breast-feeding

Age 19 or older

90 mg/day

75 mg/day

 

 

Adult smokers

125 mg/day

110 mg/day

 

 

Other

 

 

85 mg/day

120 mg/day

mg = milligrams

Maximum daily intake (from all sources) unlikely to pose risk of side effects for adults: 2,000 mg/day

Food sources include: Citrus juices and fruits, berries, tomatoes, potatoes, green and red peppers, broccoli and spinach. One cup (8 ounces) of reconstituted orange juice contains about 100 mg of vitamin C.

 What it does: Vitamin C is a water-soluble vitamin that maintains skin integrity, helps heal wounds and is important in immune functions. It also has antioxidant properties, helping to prevent cell damage by neutralizing "free radicals" — molecules believed to be associated with aging and certain diseases.

What the research says: Studies have shown that people who eat foods high in vitamin C have lower rates of cancer and heart disease, though it's unclear whether taking vitamin C supplements produces similar benefits. A 2001 study indicates that supplementation with vitamin C, certain other antioxidants and zinc may slow the progression of age-related macular degeneration (AMD), but a doctor's supervision is important to determine proper doses to lower the risk of side effects. The Institute of Medicine states that there are no established benefits for consuming vitamin C in doses higher than the RDA. Other research has suggested that 200 mg/day is the optimal dose.

Side Effects  A deficiency of vitamin C causes the disease scurvy, which is rare in the United States.

Toxicity does not normally occur, since vitamin C is water soluble and is regularly excreted by the body. Recent studies have shown, however, that excessive doses of vitamin C (many times more than the recommended amount) can lead to toxicity.

The most common manifestations of vitamin C toxicity are kidney stones, and in very rare circumstances, anemia (caused by interference with vitamin B12 absorption).
Diarrhea is also a possible but uncommon symptom associated with massively increased intake of vitamin C.

Vitamin D

Vitamin D: What is it?

Vitamin D, calciferol, is a fat-soluble vitamin. It is found in food, but also can be made in your body after exposure to ultraviolet rays from the sun. Vitamin D exists in several forms, each with a different activity. Some forms are relatively inactive in the body, and have limited ability to function as a vitamin. The liver and kidney help convert vitamin D to its active hormone form. The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. It promotes bone mineralization in concert with a number of other vitamins, minerals, and hormones. Without vitamin D, bones can become thin, brittle, soft, or misshapen. Vitamin D prevents rickets in children and osteomalacia in adults, which are skeletal diseases that result in defects that weaken bones.

What are the sources of vitamin D?

Food sources


Fortified foods are the major dietary sources of vitamin D. Prior to the fortification of milk products in the 1930s, rickets (a bone disease seen in children) was a major public health problem in the United States. Milk in the United States is fortified with 10 micrograms (400 IU) of vitamin D per quart , and rickets is now uncommon in the US. One cup of vitamin D fortified milk supplies about one-fourth of the estimated daily need for this vitamin for adults. Although milk is fortified with vitamin D, dairy products made from milk such as cheese, yogurt, and ice cream are generally not fortified with vitamin D. Only a few foods naturally contain significant amounts of vitamin D, including fatty fish and fish oils. The table of selected food sources of vitamin D suggests dietary sources of vitamin D.

Exposure to sunlight

Exposure to sunlight is an important source of vitamin D. Ultraviolet (UV) rays from sunlight trigger vitamin D synthesis in the skin. Season, latitude, time of day, cloud cover, smog, and suncreens affect UV ray exposure. For example, in Boston the average amount of sunlight is insufficient to produce significant vitamin D synthesis in the skin from November through February. Sunscreens with a sun protection factor of 8 or greater will block UV rays that produce vitamin D, but it is still important to routinely use sunscreen whenever sun exposure is longer than 10 to 15 minutes. It is especially important for individuals with limited sun exposure to include good sources of vitamin D in their diet.

Is there a Recommended Dietary Allowance for vitamin D for adults?

The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each life-stage and gender group. There is insufficient evidence to establish a RDA for vitamin D. Instead, an Adequate Intake (AI), a level of intake sufficient to maintain healthy blood levels of an active form of vitamin D, has been established. The 1998 AIs for vitamin D for adults, in micrograms (mcg) and International Units (IUs) are:

Life-Stage

 Men

 Women

Ages 19-50

5 mcg* or 200 IU

5 mcg* or 200 IU

Ages 51-69

10 mcg* or 400 IU

10 mcg* or 400 IU

Ages 70 +

15 mcg* or 600 IU

15 mcg* or 600 IU

*1 mcg vitamin D = 40 International Units (IU)

When can vitamin D deficiency occur?

A deficiency of vitamin D can occur when dietary intake of vitamin D is inadequate, when there is limited exposure to sunlight, when the kidney cannot convert vitamin D to its active form, or when someone cannot adequately absorb vitamin D from the gastrointestinal tract. The classic vitamin D deficiency diseases are rickets and osteomalacia. In children, vitamin D deficiency causes rickets, which results in skeletal deformities. In adults, vitamin D deficiency can lead to osteomalacia, which results in muscular weakness in addition to weak bones.

Who may need extra vitamin D to prevent a deficiency?

Older Americans (greater than age 50) are thought to have a higher risk of developing vitamin D deficiency. The ability of skin to convert vitamin D to its active form decreases as we age. The kidneys, which help convert vitamin D to its active form, sometimes do not work as well when people age. Therefore, some older Americans may need vitamin D from a supplement.

It is important for individuals with limited sun exposure to include good sources of vitamin D in their diets. Homebound individuals, people living in northern latitudes such as in New England and Alaska, women who cover their body for religious reasons, and individuals working in occupations that prevent exposure to sunlight are at risk of a vitamin D deficiency. If these individuals are unable to meet their daily dietary need for vitamin D, they may need a supplement of vitamin D. Individuals who have reduced ability to absorb dietary fat (fat malabsorption) may need extra vitamin D because it is a fat soluble vitamin. Some causes of fat malabsorption are pancreatic enzyme deficiency, Crohn’s disease, cystic fibrosis, sprue, liver disease, surgical removal of part or all of the stomach, and small bowel disease. Symptoms of fat malabsorption include diarrhea and greasy stools.

Vitamin D supplements are often recommended for exclusively breast-fed infants because human milk may not contain adequate vitamin D. The Institute of Medicine states that "With habitual small doses of sunshine breast- or formula-fed infants do not require supplemental vitamin D." Mothers of infants who are exclusively breastfed and have a limited sun exposure should consult with a pediatrician on this issue. Since infant formulas are routinely fortified with vitamin D, formula fed infants usually have adequate dietary intake of vitamin D.

What are some current issues and controversies about vitamin D?

Vitamin D and osteoporosis

It is estimated that over 25 million adults in the United States have, or are at risk of developing osteoporosis. Osteoporosis is a disease characterized by fragile bones. It results in increased risk of bone fractures. Having normal storage levels of vitamin D in your body helps keep your bones strong and may help prevent osteoporosis in elderly, non-ambulatory individuals, in post-menopausal women, and in individuals on chronic steroid therapy.  Researchers know that normal bone is constantly being remodeled (broken down and rebuilt). During menopause, the balance between these two systems is upset, resulting in more bone being broken down (resorbed) than rebuilt. Estrogen replacement, which limits symptoms of menopause, can help slow down the development of osteoporosis by stimulating the activity of cells that rebuild bone.

Vitamin D deficiency, which occurs more often in post-menopausal women and older Americans, has been associated with greater incidence of hip fractures. A greater vitamin D intake from diet and supplements has been associated with less bone loss in older women. Since bone loss increases the risk of fractures, vitamin D supplementation may help prevent fractures resulting from osteoporosis. In a group of women with osteoporosis hospitalized for hip fractures, 50 percent were found to have signs of vitamin D deficiency. Treatment of vitamin D deficiency can result in decreased incidence of hip fractures, and daily supplementation with 20 mcg (800 IU) of vitamin D may reduce the risk of osteoporotic fractures in elderly populations with low blood levels of vitamin D.  Your physician will discuss your need for vitamin D supplementation as part of an overall plan to prevent and/or treat osteoporosis when indicated.

Vitamin D and cancer

Laboratory, animal, and epidemiologic evidence suggest that vitamin D may be protective against some cancers. Some dietary surveys have associated increased intake of dairy foods with decreased incidence of colon cancer. Another dietary survey associated a higher calcium and vitamin D intake with a lower incidence of colon cancer. Well-designed clinical trials need to be conducted to determine whether vitamin D deficiency increases cancer risk, or if an increased intake of vitamin D is protective against some cancers. Until such trials are conducted, it is premature to advise anyone to take vitamin D supplements to prevent cancer.

Vitamin D and steroids

Corticosteroid medications are often prescribed to reduce inflammation from a variety of medical problems. These medicines may be essential for a person’s medical treatment, but they have potential side effects, including decreased calcium absorption. There is some evidence that steroids may also impair vitamin D metabolism, further contributing to the loss of bone and development of osteoporosis associated with steroid medications. For these reasons, individuals on chronic steroid therapy should consult with their physician or registered dietitian about the need to increase vitamin D intake through diet and/or dietary supplements.

Vitamin D and Alzheimer’s Disease

Adults with Alzheimer’s disease have increased risk of hip fractures. This may be because many Alzheimer’s patients are homebound, and frequently sunlight deprived. Alzheimer’s disease is more prevalent in older populations, so the fact that the ability of skin to convert vitamin D to its active form decreases as we age also may contribute to increased risk of hip fractures in this group. One study of women with Alzheimer’s disease found that decreased bone mineral density was associated with a low intake of vitamin D and inadequate sunlight exposure. Physicians evaluate the need for vitamin D supplementation as part of an overall treatment plan for adults with Alzheimer’s disease.

What is the health risk of too much vitamin D?

There is a high health risk associated with consuming too much vitamin D. Vitamin D toxicity can cause nausea, vomiting, poor appetite, constipation, weakness, and weight loss. It can also raise blood levels of calcium , causing mental status changes such as confusion. High blood levels of calcium also can cause heart rhythm abnormalities. Calcinosis, the deposition of calcium and phosphate in soft tissues like the kidney can be caused by vitamin D toxicity.

Consuming too much vitamin D through diet alone is not likely unless you routinely consume large amounts of cod liver oil. It is much more likely to occur from high intakes of vitamin D in supplements. The Food and Nutrition Board of the Institute of Medicine considers an intake of 25 mcg (1,000 IU) for infants up to 12 months of age and 50 mcg (2,000 IU) for children, adults, pregnant, and lactating women to be the tolerable upper intake level (UL). A daily intake above the UL increases the risk of adverse health effects and is not advised.

 Selected Food Sources of Vitamin D

As the 2000 Dietary Guidelines for Americans state, "Different foods contain different nutrients. No single food can supply all the nutrients in the amounts you need". The following table suggests dietary sources of vitamin D. As the table indicates, fortified foods are a major source of vitamin D. Breakfast cereals, pastries, breads, crackers, cereal grain bars and other foods may be fortified with 10% to 15% of the DV for vitamin D. It is important to read the nutrition facts panel of the food label to determine whether a food provides vitamin D. 

Table of Selected Food Sources of Vitamin D

Food

International Units

%DV *

Cod Liver Oil, 1 Tbs.

1,360 IU

340

Salmon, cooked, 3 1/2 oz

360 IU

90

Mackerel, cooked, 3 1/2 oz

345 IU

90

Sardines, canned in oil, drained,3 1/2 oz

270 IU

70

Eel, cooked, 3 1/2 oz

200 IU

50

Milk, nonfat, reduced fat, and whole, vitamin D fortified, 1 c

98 IU

25

Margarine, fortified, 1 Tbs.

60 IU

15

Cereal grain bars, fortified w/ 10% of the DV, 1 each

50 IU

10

Pudding, 1/2 c prepared from mix and made with vitamin D fortified milk

50 IU

10

Dry cereal, Vit D fortified w/10%* of DV, 3/4 c
* Other cereals may be fortified with more or less vitamin D

40-50 IU

10

Liver, beef, cooked, 3 1/2 oz

30 IU

8

Egg, 1 whole (vitamin D is present in the yolk)

25 IU

6

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains very much of a specific nutrient. The DV for vitamin D is 400 IU. The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving. Percent DVs are based on a 2,000-calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV will contribute to a healthful diet.

Vitamin E

Vitamin E: What is it?

Vitamin E is a fat-soluble vitamin that exists in eight different forms. Each form has its own biological activity, the measure of potency or functional use in the body. Alpha-tocopherol is the most active form of vitamin E in humans, and is a powerful biological antioxidant. Antioxidants such as vitamin E act to protect your cells against the effects of free radicals, which are potentially damaging by-products of the body’s metabolism. Free radicals can cause cell damage that may contribute to the development of cardiovascular disease and cancer. Studies are underway to determine whether vitamin E might help prevent or delay the development of those chronic diseases.

What foods provide vitamin E?

Vegetable oils, nuts, and green leafy vegetables are the main dietary sources of vitamin E. Fortified cereals are also an important source of vitamin E in the United States. The table of selected food sources of vitamin E suggests foods that contain vitamin E.

What is the Recommended Dietary Allowance for vitamin E for adults?

The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each life-stage and gender group. The 2000 RDAs for vitamin E for adults, in milligrams (mg) and International Units (IUs) are:

Life-Stage

 Men and Women

 Pregnancy

 Lactation

Ages 19+

15 mg* or 22 IU

 

 

All ages

 

15 mg* or 22 IU

19 mg* or 28 IU

*1 mg alpha-tocopherol equivalents = 1.5 IU

The RDA for vitamin E is based on the alpha-tocopherol form because it is the most active, or usable, form. Unlike other vitamins, the form of alpha-tocopherol made in the laboratory and found in supplements is not identical to the natural form, and is not quite as active as the natural form.

When can vitamin E deficiency occur?

Vitamin E deficiency is rare in humans. There are three specific situations when a vitamin E deficiency is likely to occur. It is seen in persons who cannot absorb dietary fat, has been found in premature, very low birth weight infants (birth weights less than 1500 grams, or 3 1/2 pounds), and is seen in individuals with rare disorders of fat metabolism. A vitamin E deficiency is usually characterized by neurological problems due to poor nerve conduction.

 Who may need extra vitamin E to prevent a deficiency?

Individuals who cannot absorb fat may require a vitamin E supplement because some dietary fat is needed for the absorption of vitamin E from the gastrointestinal tract. Anyone diagnosed with cystic fibrosis, individuals who have had part or all of their stomach removed, and individuals with malabsorptive problems such as Crohn’s disease may not absorb fat and should discuss the need for supplemental vitamin E with their physician. People who cannot absorb fat often pass greasy stools or have chronic diarrhea.

Very low birth weight infants may be deficient in vitamin E. These infants are usually under the care of a neonatologist, a pediatrician specializing in the care of newborns, who evaluates and treats the exact nutritional needs of premature infants. Abetalipoproteinemia is a rare inherited disorder of fat metabolism that results in poor absorption of dietary fat and vitamin E. The vitamin E deficiency associated with this disease causes problems such as poor transmission of nerve impulses, muscle weakness, and degeneration of the retina that can cause blindness. Individuals with abetalipoproteinemia may be prescribed special vitamin E supplements by a physician to treat this disorder.

What are some current issues and controversies about vitamin E?

Vitamin E and heart disease

Preliminary research has led to a widely held belief that vitamin E may help prevent or delay coronary heart disease. Researchers are fairly certain that oxidative modification of LDL-cholesterol (sometimes called "bad" cholesterol) promotes blockages in coronary arteries that may lead to atherosclerosis and heart attacks. Vitamin E may help prevent or delay coronary heart disease by limiting the oxidation of LDL-cholesterol. Vitamin E also may help prevent the formation of blood clots, which could lead to a heart attack. Observational studies have associated lower rates of heart disease with higher vitamin E intake. A study of approximately 90,000 nurses suggested that the incidence of heart disease was 30% to 40% lower among nurses with the highest intake of vitamin E from diet and supplements. The range of intakes from both diet and supplements in this group was 21.6 to 1,000 IU (32 to 1,500 mg), with the median intake being 208 IU.

 Vitamin E and cancer

Antioxidants such as vitamin E help protect against the damaging effects of free radicals, which may contribute to the development of chronic diseases such as cancer. Vitamin E also may block the formation of nitrosamines, which are carcinogens formed in the stomach from nitrites consumed in the diet. It also may protect against the development of cancers by enhancing immune function. Unfortunately, human trials and surveys that tried to associate vitamin E with incidence of cancer have been generally inconclusive.

Some evidence associates higher intake of vitamin E with a decreased incidence of prostate cancer and breast cancer. However, an examination of the effect of dietary factors, including vitamin E, on incidence of postmenopausal breast cancer in over 18,000 women from New York State did not associate a greater vitamin E intake with a reduced risk of developing breast cancer.  A study of women in Iowa provided evidence that an increased dietary intake of vitamin E may decrease the risk of colon cancer, especially in women under 65 years of age. On the other hand, vitamin E intake was not statistically associated with risk of colon cancer in almost 2,000 adults with cancer who were compared to controls without cancer. At this time there is limited evidence to recommend vitamin E supplements for the prevention of cancer.

Vitamin E and cataracts

Cataracts are growths on the lens of the eye that cloud vision. They increase the risk of disability and blindness in aging adults. Antioxidants are being studied to determine whether they can help prevent or delay cataract growth. Observational studies have found that lens clarity, which is used to diagnose cataracts, was better in regular users of vitamin E supplements and in persons with higher blood levels of vitamin E. A study of middle aged male smokers, however, did not demonstrate any effect from vitamin E supplements on the incidence of cataract formation. The effects of smoking, a major risk factor for developing cataracts, may have overridden any potential benefit from the vitamin E, but the conflicting results also indicate a need for further studies before researchers can confidently recommend extra vitamin E for the prevention of cataracts.

What is the health risk of too much vitamin E?

The health risk of too much vitamin E is low. A recent review of the safety of vitamin E in the elderly indicated that taking vitamin E supplements for up to four months at doses of 530 mg or 800 IU (35 times the current RDA) had no significant effect on general health, body weight, levels of body proteins, lipid levels, liver or kidney function, thyroid hormones, amount or kinds of blood cells, and bleeding time. Even though this study provides evidence that taking a vitamin E supplement containing 530 mg or 800 IU for four months is safe, the long term safety of vitamin E supplementation has not been tested. The Institute of Medicine has set an upper tolerable intake level for vitamin E at 1,000 mg (1,500 IU) for any form of supplementary alpha-tocopherol per day because the nutrient can act as an anticoagulant and increase the risk of bleeding problems. Upper tolerable intake levels "represent the maximum intake of a nutrient that is likely to pose no risk of adverse health effects in almost all individuals in the general population".

Table of Selected Food Sources of vitamin E 

As the 2000 Dietary Guidelines for Americans state, "Different foods contain different nutrients. No single food can supply all the nutrients in the amounts you need". The following table lists selected sources of vitamin E. As the tables indicate, vegetables oils, nuts, and green leafy vegetables are good dietary sources of vitamin E. Including these foods in your diet will help you meet your daily need for vitamin E, but it is still important to moderate total fat intake as recommended by the Dietary Guidelines for Americans.

Food manufacturers fortify many foods with vitamins and minerals. It is important to read the nutrition facts panel of the food label to determine whether a food provides vitamin E.

Table of Food Sources

Food

International Units

%DV*

Wheat germ oil, 1 Tb

26.2

90

Almonds, dry roasted, 1 oz

7.5

25

Safflower oil, 1 TB

4.7

15

Corn oil, 1 TB

2.9

10

Soybean oil, 1 TB

2.5

8

Turnip greens, frozen, boiled, 1/2 c

2.4

8

Mango, raw, without refuse,1 fruit

2.3

8

Peanuts, dry roasted, 1 oz

2.1

8

Mixed nuts w/ peanuts, oil roasted, 1 oz

1.7

6

Mayonnaise, made w/ soybean oil, 1 TB

1.6

6

Broccoli, frozen, chopped, boiled, 1/2 c

1.5

6

Dandelion greens, boiled, 1/2 c

1.3

4

Pistachio nuts, dry roasted, 1 oz

1.2

4

Spinach, frozen, boiled, 1/2 c

0.85

2

Kiwi, 1 medium fruit

0.85

2

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for vitamin E is 30 International Units (or 20 mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving. Percent DVs are based on a 2,000-calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV will contribute to a healthful diet.

 

Folate

Folate: What is it?

Folate and folic acid are forms of a water-soluble B vitamin. Folate occurs naturally in food. Folic acid is the synthetic form of this vitamin that is found in supplements and fortified foods. Folate gets its name from the Latin word "folium" for leaf. A key observation of researcher Lucy Wills nearly 70 years ago led to the identification of folate as the nutrient needed to prevent the anemia of pregnancy. Dr. Wills demonstrated that the anemia could be corrected by a yeast extract. Folate was identified as the corrective substance in yeast extract in the late 1930s and was extracted from spinach leaves in 1941. Folate is necessary for the production and maintenance of new cells. This is especially important during periods of rapid cell division and growth such as infancy and pregnancy. Folate is needed to make DNA and RNA, the building blocks of cells. It also helps prevent changes to DNA that may lead to cancer. Both adults and children need folate to make normal red blood cells and prevent anemia.

What foods provide folate?

Leafy greens such as spinach and turnip greens, dry beans and peas, fortified cereals and grain products, and some fruits and vegetables are rich food sources of folate. Some breakfast cereals (ready-to-eat and others) are fortified with 25 percent or 100 percent of the Daily Value (DV) for folic acid. The table of selected food sources of folate and folic acid suggests dietary sources of this vitamin. In 1996, the Food and Drug Administration (FDA) published regulations requiring the addition of folic acid to enriched breads, cereals, flours, corn meals, pastas, rice, and other grain products. This ruling took effect January 1, 1998, and was specifically targeted to reduce the risk of neural tube birth defects in newborns. Since the folic acid fortification program took effect, fortified foods have become a major source of folic acid in the American diet. Synthetic folic acid that is added to fortified foods and dietary supplements has a simpler chemical structure than the natural form of folate, and is absorbed more easily by the body. After digestion and absorption however, the two forms are identical and function in exactly the same manner.

What is the Recommended Dietary Allowance for folate for adults?

The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97 to 98 percent) healthy individuals in each life-stage and gender group. The 1998 RDAs for folate are expressed in a term called the Dietary Folate Equivalent. The Dietary Folate Equivalent (DFE) was developed to help account for the differences in absorption of naturally occurring dietary folate and the more bioavailable synthetic folic acid.

Life Stage

 Men

 Women

 Pregnancy

 Lactation

Ages 19+

400 mcg

 400 mcg

 

 

All ages

 

 

600 mcg  

500 mcg

I mcg of food folate = 0.6 mcg folic acid from supplements and fortified foods

The National Health and Nutrition Examination Survey (NHANES III 1988-91) and the Continuing Survey of Food Intakes by Individuals (1994-96 CSFII) indicated that most adults did not consume adequate folate. However, the folic acid fortification program has increased folic acid content of commonly eaten foods such as cereals and grains, and as a result diets of most adults now provide recommended amounts of folate equivalents.

When can folate deficiency occur?

A deficiency of folate can occur when your need for folate is increased, when dietary intake of folate is inadequate, and when your body excretes (or loses) more folate than usual. Medications that interfere with your body's ability to use folate may also increase the need for this vitamin. Some situations that increase the need for folate include:

  •  pregnancy and lactation (breastfeeding)
  •  alcohol abuse
  •  malabsorption
  •  kidney dialysis
  •  liver disease
  •  certain anemias.

Medications can interfere with folate utilization, including:

  • anti-convulsant medications (such as dilantin, phenytoin, and primidone)
  • Metformin (sometimes prescribed to control blood sugar in type 2 diabetes)
  • Sulfasalazine (used to control inflammation associated with Crohn's disease and ulcerative colitis)
  • Triamterene (a diuretic)
  • Methotrexate.

Signs of folate deficiency

Signs of folic acid deficiency are often subtle. Diarrhea, loss of appetite, and weight loss can occur. Additional signs are weakness, sore tongue, headaches, heart palpitations, irritability, and behavioral disorders. Women with folate deficiency who become pregnant are more likely to give birth to low birth weight and premature infants, and infants with neural tube defects. In adults, anemia is a sign of advanced folate deficiency. In infants and children, folate deficiency can slow growth rate. Some of these symptoms can also result from a variety of medical conditions other than folate deficiency. It is important to have a physician evaluate these symptoms so that appropriate medical care can be given.

Who may need extra folic acid to prevent a deficiency?

Women of childbearing age, people who abuse alcohol, anyone taking anti-convulsants or other medications that interfere with the action of folate, individuals diagnosed with anemia from folate deficiency, and individuals with malabsorption, liver disease, or who are receiving kidney dialysis treatment may benefit from a folic acid supplement.

Folic acid is very important for all women who may become pregnant. Adequate folate intake during the periconceptual period, the time just before and just after a woman becomes pregnant, protects against a number of congenital malformations including neural tube defects. Neural tube defects result in malformations of the spine (spina bifida), skull, and brain (anencephaly). The risk of neural tube defects is significantly reduced when supplemental folic acid is consumed in addition to a healthful diet prior to and during the first month following conception. Women who could become pregnant are advised to eat foods fortified with folic acid or take supplements in addition to eating folate-rich foods to reduce the risk of some serious birth defects. Taking 400 micrograms of synthetic folic acid daily from fortified foods and/or supplements has been suggested. The Recommended Dietary Allowance (RDA) for folate equivalents for pregnant women is 600 micrograms.

Folate deficiency has been observed in alcoholics. A 1997 review of the nutritional status of chronic alcoholics found low folate status in more than 50 percent of those surveyed. Alcohol interferes with the absorption of folate and increases excretion of folate by the kidney. In addition, many alcohol abusers have poor quality diets that do not provide the recommended intake of folate. Increasing folate intake through diet, or folic acid intake through fortified foods or supplements, may be beneficial to the health of alcoholics.

Anti-convulsant medications such as dilantin increase the need for folate. Anyone taking anti-convulsants and other medications that interfere with the body's ability to use folate should consult with a medical doctor about the need to take a folic acid supplement.  Anemia is a condition that occurs when red blood cells cannot carry enough oxygen. It can result from a wide variety of medical problems, including folate deficiency. Folate deficiency can result in the formation of large red blood cells that do not contain adequate hemoglobin, the substance in red blood cells that carries oxygen to your body's cells.  Several medical conditions increase the risk of folic acid deficiency. Liver disease and kidney dialysis increase excretion (loss) of folic acid. Malabsorption can prevent your body from using folate in food. Medical doctors treating individuals with these disorders will evaluate the need for a folic acid supplement.

Caution about folic acid supplements

Beware of the interaction between vitamin B12 and folic acid. Folic acid supplements can correct the anemia associated with vitamin B12 deficiency. Unfortunately, folic acid will not correct changes in the nervous system that result from vitamin B12 deficiency. Permanent nerve damage can occur if vitamin B12 deficiency is not treated. Intake of supplemental folic acid should not exceed 1,000 micrograms (mcg) per day to prevent folic acid from masking symptoms of vitamin B12 deficiency. It is very important for older adults to be aware of the relationship between folic acid and vitamin B12 because they are at greater risk of having a vitamin B12 deficiency.

 
What are some current issues and controversies about folate?

Folic acid and heart disease

A deficiency of folate, vitamin B12, or vitamin B6 may increase the level of homocysteine, an amino acid normally found in the blood. There is evidence that an elevated homocysteine level is an independent risk factor for heart disease and stroke. The evidence suggests that high levels of homocysteine may damage coronary arteries or make it easier for blood clotting cells called platelets to clump together and form a clot. However, there is currently no evidence available to suggest that lowering homocysteine with vitamins will reduce your risk of heart disease. Clinical intervention trials are needed to determine whether supplementation with folic acid, vitamin B12 or vitamin B6 can lower your risk of developing coronary heart disease.

Folic acid and cancer

Some evidence associates low blood levels of folate with a greater risk of cancer. Folate is involved in the synthesis, repair, and functioning of DNA, our genetic map, and a deficiency of folate may result in damage to DNA that may lead to cancer. Several studies have associated diets low in folate with increased risk of breast, pancreatic, and colon cancer. Findings from a study of over 121,000 nurses suggested that long-term folic acid supplementation (for 15 years) was associated with a decreased risk of colon cancer in women aged 55 to 69 years of age. However, associations between diet and disease do not indicate a direct cause. Researchers are continuing to investigate whether enhanced folate intake from foods or folic acid supplements may reduce the risk of cancer. Until results from such clinical trials are available, folic acid supplements should not be recommended to reduce the risk of cancer.

Folic acid and methotrexate for cancer

Folate is important for cells and tissues that rapidly divide. Cancer cells divide rapidly, and drugs that interfere with folate metabolism are used to treat cancer. Methotrexate is a drug often used to treat cancer because it limits the activity of enzymes that need folate. Unfortunatley, methotrexate can be toxic (46-48), producing side effects such as inflammation in the digestive tract that make it difficult to eat normally. Leucovorin is a form of folate that can help "rescue" or reverse the toxic effects of methotrexate. It is not known whether folic acid supplements can help control the side effects of methotrexate without decreasing its effectiveness in chemotherapy.

Folic acid and methotrexate for non-cancerous diseases

Low dose methotrexate is used to treat a wide variety of non-cancerous diseases such as rheumatoid arthritis, lupus, psoriasis, asthma, sarcoidoisis, primary biliary cirrhosis, and inflammatory bowel disease. Low doses of methotrexate can deplete folate stores and cause side effects that are similar to folate deficiency. Both high folate diets and supplemental folic acid may help reduce the toxic side effects of low dose methotrexate without decreasing its effectiveness. Anyone taking low dose methotrexate for the health problems listed above should consult with a physician about the need for a folic acid supplement.

What is the health risk of too much folic acid?

The risk of toxicity from folic acid is low. The Institute of Medicine has established a tolerable upper intake level (UL) for folate of 1,000 mcg for adult men and women, and a UL of 800 mcg for pregnant and lactating (breast-feeding) women less than 18 years of age. Supplemental folic acid should not exceed the UL to prevent folic acid from masking symptoms of vitamin B12 deficiency.

Selected food sources of folate and folic acid

The following table suggests dietary sources of folate. As the table indicates, green leafy vegetables, dry beans and peas, and many other types of vegetables and fruits are good sources of folate. In addition, fortified foods are a major source of folic acid. It is not unusual to find foods such as cereals fortified with 100 percent of the RDA for folate. The variety of fortified foods available has made it easier for women of childbearing age to consume the recommended 400 mcg of folic acid per day from fortified foods and/or supplements. The large numbers of fortified foods on the market, however, also raise concern that intake may exceed the UL. This is especially important for anyone at risk of vitamin B12 deficiency, which can be masked by too much folic acid. It is important for anyone who is considering taking a folic acid supplement to first consider whether their needs are being met by adequate sources of dietary folate and folic acid from fortified foods.

Table of Food Sources of Folate

 Food

Micrograms

Dietary Folate Equivalents

%DV*

Ready to eat cereal, fortified with 100% of the DV, 3/4 c

400

100

Beef liver, cooked, braised, 3 oz

185

45

Cowpeas (blackeyes), immature, cooked, boiled, 1/2 c

105

25

Breakfast cereals, fortified with 25% of the DV, 3/4 c

100

25

Spinach, frozen, cooked, boiled, 1/2 c

100

25

Great Northern beans, boiled, 1/2 c

90

20

Asparagus, boiled, 4 spears

85

20

Wheat germ, toasted, 1/4 c

80

20

Orange juice, chilled, includes concentrate, 3/4 c

70

20

Turnip Greens, frozen, cooked, boiled, 1/2 c

65

15

Vegetarian baked beans, canned, 1 c

60

15

Spinach, raw, 1 c

60

15

Green peas, boiled, 1/2 c

50

15

Broccoli, chopped, frozen, cooked, 1/2 c

50

15

Egg noodles, cooked, enriched, 1/2 c

50

15

Rice, white, long-grain, parboiled, cooked, enriched, 1/2 c

45

10

Avocado, raw, all varieties, sliced, 1/2 c sliced

45

10

Peanuts, all types, dry roasted, 1 oz

40

10

Lettuce, Romaine, shredded, 1/2 c

40

10

Tomato Juice, canned, 6 oz

35

10

Orange, all commercial varieties, fresh, 1 small

30

8

Bread, white, enriched, 1 slice

25

6

Egg, whole, raw, fresh, 1 large

25

6

Cantaloupe, raw, 1/4 medium

25

6

Papaya, raw, 1/2 c cubes

25

6

Banana, raw, 1 medium

20

6

Broccoli, raw, 1 spear (about 5 inches long)

20

6

Lettuce, iceberg, shredded, 1/2 c

15

4

Bread, whole wheat, 1 slice

15

4

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for folic acid is 400 micrograms (mcg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet.

Iron

Iron: What is it?

Iron is an essential mineral and an important component of proteins involved in oxygen transport and metabolism. Almost two-thirds of the iron in your body is found in hemoglobin, the protein in red blood cells that carries oxygen to your body’s tissues. Smaller amounts of iron are found in myoglobin, a protein that helps supply oxygen to muscle, and in enzymes that assist biochemical reactions in cells. About 15 percent of your body’s iron is stored for future needs and mobilized when dietary intake is inadequate. The remainder is in your body’s tissues as part of proteins that help your body function. Adult men and post-menopausal women lose very little iron except through bleeding. Women with heavy monthly periods can lose a significant amount of iron. Your body usually maintains normal iron status by controlling the amount of iron absorbed from food.

What foods provide iron?

There are two forms of dietary iron: heme and nonheme. Iron in meat, fish, and poultry is found in a chemical structure known as heme. Heme iron is absorbed very efficiently by your body. Iron in plants such as lentils and beans is arranged in a different chemical structure called nonheme iron. Nonheme iron is not as well absorbed as heme iron. Flours, cereals, and grain products that are enriched or fortified with iron are good dietary sources of nonheme iron. The addition of iron to infant formulas, cereals, and grain products has been credited with improving the iron status of millions of infants, children, and women. The tables of selected food sources of heme and nonheme iron suggest many dietary sources of iron.

What affects iron absorption?

Iron absorption refers to the amount of dietary iron that your body obtains from food. Healthy adults absorb about 15% of the iron in their diet, but your actual absorption is influenced by your body’s iron stores, the type of iron in the diet, and by other dietary factors that either help or hinder iron absorption.

The greatest influence on iron absorption is the amount stored in your body. Iron absorption significantly increases when body stores are low. When iron stores are high, absorption decreases to help protect against iron overload.

Absorption of heme iron is very efficient and not significantly affected by the composition of your diet. Only 1% to 7% of the nonheme iron in vegetable staples such as rice, maize, black beans, soybeans and wheat is absorbed when consumed as a single food. However, dietary factors can significantly improve nonheme iron absorption. Meat proteins and vitamin C will improve the absorption of nonheme iron. Diets that include a minimum of 5 servings of fruits and vegetables daily, as recommended by the Food Guide Pyramid, should provide plenty of vitamin C to boost nonheme iron absorption. Calcium, polyphenols and tannins found in tea, and phytates, which are a component of plant foods such as legumes, rice and grains, can decrease the absorption of nonheme iron. Some proteins found in soybeans also inhibit nonheme iron absorption. Most healthy individuals can maintain normal iron sores when the diet provides a wide variety of foods as suggested by the Food Guide Pyramid. It is most important to include foods that enhance nonheme iron absorption when total daily iron intake does not meet the RDA, when iron losses are exceptionally high, or when no heme iron is usually consumed.

 What is the Recommended Dietary Allowance for Iron

The Recommended Dietary Allowance (RDA) is the daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each life-stage and gender group. The 2001 RDAs for iron (in milligrams) for infants ages 7 to 12 months, children and adults are:

Age

 Infants, Children

 Males

 Females

Pregnancy

 Lactation

7 to 12 months

11 mg

 

 

 

 

1 to 3 years

7 mg

 

 

 

 

4 to 8 years

1o mg

 

 

 

 

9 to 13 years

 

8 mg

8 mg

 

 

14-18 years

 

11 mg

15 mg

27 mg

10 mg

19-50 years

 

8 mg

18 mg

27 mg

9 mg

51+ years

 

8 mg

8 mg

 

 

Normal full term infants are born with a supply of iron that lasts for 4 to 6 months. Evidence is not available to establish a RDA for iron for infants from birth through 6 months of age. Recommended iron intake for infants from 0 to 6 months is based on an Adequate Intake (AI) of 0.27 milligrams (mg) per day that reflects the average iron intake of breastfed infants. Iron in human milk (breast milk) is well absorbed by infants. It is estimated that infants can use greater than 50% of the iron in breast milk as compared to typically less than 12% of the iron in infant formula. Cow milk is not only low in iron and poorly absorbed by infants, its use in infancy can cause gastrointestinal bleeding and iron loss from the body. For these reasons, cow milk should not be fed to infants until after age 1. The American Academy of Pediatrics recommends that infants who are not breastfed or who are partially breastfed should receive an iron-fortified formula from birth to 12 months. Formulas that contain between 4.0 to 12 milligrams of iron per liter of formula are considered iron-fortified.

Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III-1988-91) and the Continuing Survey of Food Intakes by Individuals (1994-96 CSFII) indicate that diets of most adult men and post-menopausal women provide recommended amounts of iron. Diets of females of childbearing age, pregnant women, and women who breast-feed generally do not provide recommended amounts of iron.

When can iron deficiency occur?

The World Health Organization considers iron deficiency the number one nutritional disorder in the world. It affects more than 30% of the world’s population.  When your need for iron increases or a loss of iron from bleeding exceeds your dietary iron intake, a negative iron balance may occur. Initially this results in iron depletion, in which the storage form of iron is decreased while blood hemoglobin level remains normal. Iron deficiency occurs when blood and storage levels of iron are low, and the blood hemoglobin level falls below normal.

Iron deficiency anemia may result from a low dietary intake, inadequate intestinal absorption, excessive blood loss, and/or increased needs. Women of childbearing age, pregnant women, older infants and toddlers, and teenage girls are at greatest risk of developing iron deficiency anemia because they have the greatest needs.  Individuals with renal failure, especially those receiving dialysis, are at high risk for developing iron deficiency anemia. This is because their kidneys cannot create enough erythropoietin, a hormone needed to make red blood cells. Iron and erythropoietin can also be lost with blood during dialysis, which can result in an iron deficiency. Extra iron and erythropoietin are usually needed to help prevent iron deficiency in these individuals.

Iron deficiency could also be caused by low vitamin A status. Vitamin A helps to mobilize iron from its storage sites, so a deficiency of vitamin A limits the body’s ability to use stored iron. This results in an “apparent” iron deficiency because hemoglobin levels are low, even though the body can maintain normal amounts of stored iron. While uncommon in the U.S., this problem is seen in developing countries where vitamin A deficiency often occurs.  The anemia that may occur with inflammatory disease differs from iron deficiency anemia. It occurs in people who have chronic infectious, inflammatory, or malignant disorders. It is not associated with a shortage of dietary iron, and may not respond to iron supplementation. A physician should manage anemia associated with an inflammatory disorder.

Signs of iron deficiency anemia include feeling tired and weak, decreased work and school performance, slow cognitive and social development during childhood, difficulty maintaining body temperature, and decreased immune function, which may decrease resistance to infection. During pregnancy, iron deficiency is associated with increased risk of premature deliveries, giving birth to infants with low birth weight, and maternal complications.

Who may need extra iron to prevent a deficiency?

Iron deficiency and iron deficiency anemia are relatively common in women of childbearing age, older infants and toddlers, and teenage girls, so they should periodically be screened for iron deficiency. Within these groups, iron deficiency is more common among women with heavy menstrual losses, women belonging to minority and low-income groups, and women who have had more than one child . Women taking oral contraceptives may experience less bleeding during their periods and have a lower risk of developing an iron deficiency while women using an intrauterine device (IUD) may experience more bleeding and have a greater risk of developing an iron deficiency. If laboratory tests indicate iron deficiency, iron supplements may be recommended. Many physicians routinely prescribe iron supplements during pregnancy because of the high incidence of iron deficiency anemia in pregnant women and the potential benefits for the mother and the fetus. Pregnancy increases a woman’s need for iron due to increased blood volume, increased needs of the fetus, and blood losses that occur during delivery.

Excluding all meat and meat products, poultry, and fish from your diet may reduce your total iron intake and will decrease your intake of heme iron, which is easily absorbed by your body. It will also influence your iron status because animal proteins can improve the absorption of nonheme iron found in plant foods. Vegetarians who exclude all animal products from their diet may need twice as much dietary iron because the intestinal absorption of nonheme iron is lower in plant foods. Vegetarians should also consider consuming nonheme iron sources together with a good source of vitamin C, such as citrus fruits or certain vegetables, to enhance absorption of nonheme iron.

Some facts about iron supplements

Iron supplementation is indicated when an iron deficiency is diagnosed and diet alone cannot restore bodily iron content to normal levels within an acceptable timeframe. Iron in supplements comes in two forms: ferrous and ferric. The ferrous form is better absorbed and is usually the preferred form when iron deficiency has been diagnosed.  Supplemental iron may cause gastrointestinal side effects such as nausea, vomiting, constipation, diarrhea, dark colored stools, and/or abdominal distress. To minimize these side effects, start with half the recommended dose, gradually increasing to the full dose. Taking the supplement in divided doses and with food also may help limit these symptoms.

Who should be cautious about taking iron supplements?

Iron deficiency is uncommon among adult men and postmenopausal women. These individuals should only take iron supplements when prescribed by their qualified health care provider because of the risk of iron overload. Iron overload is a condition in which excess iron is found in the blood and stored in organs such as the liver and heart. Iron overload is associated with several genetic diseases including hemochromatosis, which affects approximately 1 in 250 individuals of northern European descent. Individuals with hemochromatosis absorb iron very efficiently, which can result in a build up of excess iron in organs and can cause organ damage such as cirrhosis of the liver and heart failure. This condition often is not diagnosed until the excess iron stores have damaged an organ. Iron supplementation may accelerate the effects of hemochromatosis, an important reason why adult men and postmenopausal women who are not iron deficient should not take iron supplements. Individuals with blood disorders who require frequent blood transfusions are also at risk of iron overload and should not take iron supplements.

What are some current issues and controversies about iron?

Iron and Heart Disease

Several observations have led researchers to examine the association between high iron stores and coronary heart disease. It appears that rates of heart disease among women increase when monthly periods stop, a time when levels of stored iron increase. Also, some researchers have suggested that lower rates of heart disease among people living in developing countries may be due to low meat (and iron) intake, high fiber diets that inhibit iron absorption, and gastrointestinal (GI) parasite concentrations that result in gastrointestinal blood (and iron) loss, all of which contribute to low iron stores in this population.

Iron and Cancer

Individuals with hereditary hemochromatosis are at increased risk for liver cancer. This increased risk is associated with an accumulation of iron in the liver, which can result in increased production of free radicals. Free radicals are by-products of normal metabolism that can damage your body’s cells. There is inconclusive evidence that iron status is associated with the incidence of cancer in those who do not have hereditary hemochromatosis.

Iron and Intense Exercise

Many men and women who engage in regular intense exercise have marginal or inadequate iron status. Researchers have estimated that daily iron loss increases in those who engage in regular exercise. Research also indicates that iron has a shorter biologic half-life in highly trained runners. For these reasons, the need for iron may be 30% greater in those who engage in regular intense exercise.

Iron fortification and absorption of other nutrients

Some researchers have raised concerns about the effects of iron fortification and supplementation on the absorption of other nutrients such as zinc, calcium, and copper. Research studies have shown that supplemental iron may decrease the absorption of these nutrients, but generally only when the supplement is taken on an empty stomach. Absorption of these nutrients is generally not affected when supplementary iron is taken with food.

 What is the health risk of too much iron?

Iron has a moderate to high potential for toxicity because very little iron is excreted from the body. Thus, iron can accumulate in body tissues and organs when normal storage sites are full.  In children, acute toxicity can occur from overdoses of medicinal iron. Ingestion of as few as five or six high-potency tablets can provide amounts of iron that can be fatal to a child of 22 pounds. Consuming 1 to 3 grams of iron can be fatal to children under six and lower doses can cause severe symptoms such as vomiting and diarrhea. It is important to keep iron supplements tightly capped and away from children’s reach. Any time excessive iron intake is suspected, immediately call your physician or Poison Control Center, or visit your local emergency room. In adults high intakes of iron supplements are associated with constipation, nausea, vomiting, and diarrhea, especially when the supplements are taken on an empty stomach .

In 2001, the Institute of Medicine set a tolerable upper intake level (UL) of 40 mg per day for infants and children through age 13 and 45 mg per day for adolescents ages 14 to 18 years and adults 19 years of age and older. The upper limit does not apply to individuals who receive iron under medical supervision. There may be times when a medical doctor prescribes an intake higher than the upper limit, such as when individuals with iron deficiency anemia need higher doses of iron until their iron stores return to normal.

Selected Food Sources of Iron

As the 2000 Dietary Guidelines for Americans state, “Different foods contain different nutrients and other healthful substances. No single food can supply all the nutrients in the amounts you need”. The following tables suggest dietary sources of heme and nonheme iron. As the table indicates, meat, poultry, fish and seafood are good sources of heme iron and beans are good sources of nonheme iron. In addition, many foods are fortified with iron. Some foods, such as cereals, may be fortified with 100% of the Daily Value (DV)* for iron.

Table of Food Sources of Heme Iron

 Food

 Milligrams

%DV*

Chicken liver, cooked, 3 ounces

7.0

40

Oysters, breaded and fried, 6

4.5

25

Beef, chuck, braised, 3 ounces

3.2

20

Clams, breaded, fried, 3/4 cup

3.0

15

Beef, tenderloin, roasted, 3 ounces

3.0

15

Turkey, dark meat, roasted, 3 ounces

2.0

10

Beef, eye of round, roasted, 3 ounces

1.7

10

Turkey, light meat, roasted, 3 ounces

1.2

6

Tuna, fresh bluefin, cooked, dry heat, 3 ounces

1.1

6

Chicken, leg, meat only, roasted, 3 ounces

1.1

6

Crab, blue crab, flaked & pieces, cooked, moist heat, 1 cup

1.1

6

Chicken, breast, roasted, 3 ounces

1.0

5

Halibut, cooked, dry heat, 3 ounces

0.9

5

Pork, loin, meat only, broiled, 3 ounces

0.8

4

Tuna, white, canned in water, 3 ounces

0.8

4

Crab, blue crab, cooked, moist heat, 3 ounces

0.8

4

Shrimp, mixed species, cooked, moist heat, 4 large

0.7

4

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for iron is 18 milligrams (mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided in one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet.

Table of Food Sources of Nonheme Iron

 Food

 Milligrams

%DV*

Ready-to-eat cereal, 100% fortified, 3/4 cup

18.0

100

Ready-to-eat cereal, 50% fortified, 3/4 cup

9.0

50

Soybeans, mature, cooked, boiled, 1 cup

8

50

Lentils, cooked, boiled, 1 cup.

6

35

Grits, white, enriched, instant, 1 packet prepared

5.4

30

Oatmeal, instant, fortified, 1/2 cup

4.1

25

Kidney beans, cooked, boiled, 1 cup

5.2

25

Pinto beans, cooked, boiled, 1 cup

4.6

25

Lima beans, cooked, boiled, 1 cup

4.2

25

Navy beans, cooked, boiled, 1 cup

3.8

20

Black beans, cooked, boiled, 1 cup

3.6

20

Spinach, cooked, boiled, drained, 1/2 cup

3.2

20

Spinach, canned, drained solids 1/2 cup

2.5

10

Tofu, firm, 1/2 cup

1.8

10

Black-eyed-peas, cooked, boiled, 1 cup

1.8

10

Spinach, frozen, cooked, boiled 1/2 cup

1.4

8

Whole wheat bread, 1 slice

0.9

5

Molasses, 1 Tablespoon

0.9

5

White bread, enriched, 1 slice

0.8

4

Raisins, seedless, 50

0.5

2

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for iron is 18 milligrams (mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided in one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet.

Magnesium

Magnesium: What is it?

Magnesium is a mineral needed by every cell of your body. About half of your body's magnesium stores are found inside cells of body tissues and organs, and half are combined with calcium and phosphorus in bone. Only 1 percent of the magnesium in your body is found in blood. Your body works very hard to keep blood levels of magnesium constant. Magnesium is needed for more than 300 biochemical reactions in the body. It helps maintain normal muscle and nerve function, keeps heart rhythm steady, and bones strong. It is also involved in energy metabolism and protein synthesis.

What foods provide magnesium?

Green vegetables such as spinach provide magnesium because the center of the chlorophyll molecule contains magnesium. Nuts, seeds, and some whole grains are also good sources of magnesium.


Although magnesium is present in many foods, it usually occurs in small amounts. As with most nutrients, daily needs for magnesium cannot be met from a single food. Eating a wide variety of foods, including five servings of fruits and vegetables daily and plenty of whole grains, helps to ensure an adequate intake of magnesium. The magnesium content of refined foods is usually low. Whole-wheat bread, for example, has twice as much magnesium as white bread because the magnesium-rich germ and bran are removed when white flour is processed. The table of food sources of magnesium suggests many dietary sources of magnesium. Water can provide magnesium, but the amount varies according to the water supply. "Hard" water contains more magnesium than "soft" water. Dietary surveys do not estimate magnesium intake from water, which may lead to underestimating total magnesium intake and its variability.

 What is the Recommended Dietary Allowance for magnesium?

The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98 percent) individuals in each life-stage and gender group. The 1999 RDAs for magnesium for adults, in milligrams (mg), are:

Life-Stage

 Men

 Women

 Pregnancy

 Lactation

Ages 14 - 18

410 mg

 360 mg

400 mg

 360 mg

Ages 19 - 30

400 mg

 310 mg

350 mg  

 310 mg

Ages 31 +

420 mg

 320 mg

360 mg

 320 mg

Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III-1988-91) (5) and the Continuing Survey of Food Intakes of Individuals (1994 CSFII) (4), indicated that the diets of most adult men and women do not provide the recommended amounts of magnesium. The surveys also suggested that adults age 70 and over eat less magnesium than younger adults, and that non-Hispanic black subjects consumed less magnesium than either non-Hispanic white or Hispanic subjects.

When can magnesium deficiency occur?

Even though dietary surveys suggest that many Americans do not consume magnesium in recommended amounts, magnesium deficiency is rarely seen in the United States in adults. When magnesium deficiency does occur, it is usually due to excessive loss of magnesium in urine, gastrointestinal system disorders that cause a loss of magnesium or limit magnesium absorption, or a chronically low intake of magnesium.

Treatment with diuretics (water pills), some antibiotics, and some medicine used to treat cancer, such as Cisplatin, can increase the loss of magnesium in urine. Poorly controlled diabetes increases loss of magnesium in urine, causing a depletion of magnesium stores. Alcohol also increases excretion of magnesium in urine, and a high alcohol intake has been associated with magnesium deficiency. Gastrointestinal problems, such as malabsorption disorders, can cause magnesium depletion by preventing the body from using the magnesium in food. Chronic or excessive vomiting and diarrhea may also result in magnesium depletion. Signs of magnesium deficiency include confusion, disorientation, loss of appetite, depression, muscle contractions and cramps, tingling, numbness, abnormal heart rhythms, coronary spasm, and seizures.

Who may need extra magnesium?

Healthy adults who eat a varied diet do not generally need to take a magnesium supplement. Magnesium supplementation is usually indicated when a specific health problem or condition causes an excessive loss of magnesium or limits magnesium absorption. Extra magnesium may be required by individuals with conditions that cause excessive urinary loss of magnesium, chronic malabsorption, severe diarrhea and steatorrhea, and chronic or severe vomiting. Loop and thiazide diuretics, such as Lasix, Bumex, Edecrin, and Hydrochlorothiazide, can increase loss of magnesium in urine. Medicines such as Cisplatin, which is widely used to treat cancer, and the antibiotics Gentamicin, Amphotericin, and Cyclosporin also cause the kidneys to excrete (lose) more magnesium in urine. Doctors routinely monitor magnesium levels of individuals who take these medicines and prescribe magnesium supplements if indicated.

Poorly controlled diabetes increases loss of magnesium in urine and may increase an individual's need for magnesium. A medical doctor would determine the need for extra magnesium in this situation. Routine supplementation with magnesium is not indicated for individuals with well-controlled diabetes. People who abuse alcohol are at high risk for magnesium deficiency because alcohol increases urinary excretion of magnesium. Low blood levels of magnesium occur in 30 percent to 60 percent of alcoholics, and in nearly 90 percent of patients experiencing alcohol withdrawal. In addition, alcoholics who substitute alcohol for food will usually have lower magnesium intakes. Medical doctors routinely evaluate the need for extra magnesium in this population.

The loss of magnesium through diarrhea and fat malabsorption usually occurs after intestinal surgery or infection, but it can occur with chronic malabsorptive problems such as Crohn's disease, gluten sensitive enteropathy, and regional enteritis. Individuals with these conditions may need extra magnesium. The most common symptom of fat malabsorption, or steatorrhea, is passing greasy, offensive-smelling stools. Occasional vomiting should not cause an excessive loss of magnesium, but conditions that cause frequent or severe vomiting may result in a loss of magnesium large enough to require supplementation. In these situations, your medical doctor would determine the need for a magnesium supplement. Individuals with chronically low blood levels of potassium and calcium may have an underlying problem with magnesium deficiency. Adding magnesium supplements to their diets may make potassium and calcium supplementation more effective for them. Doctors routinely evaluate magnesium status when potassium and calcium levels are abnormal, and prescribe a magnesium supplement when indicated.

What is the best way to get extra magnesium?

Doctors will measure blood levels of magnesium whenever a magnesium deficiency is suspected. When levels are mildly depleted, increasing dietary intake of magnesium can help restore blood levels to normal. Eating at least five servings of fruits and vegetables daily, and choosing dark-green leafy vegetables often, as recommended by the Dietary Guidelines for Americans, the Food Guide Pyramid, and the Five-a-Day program, will help adults at-risk of having a magnesium deficiency consume recommended amounts of magnesium. When blood levels of magnesium are very low, an intravenous drip (IV drip) may be needed to return levels to normal. Magnesium tablets also may be prescribed, but some forms, in particular magnesium salts, can cause diarrhea. Your medical doctor or qualified health-care provider can recommend the best way to get extra magnesium when it is needed.


What are some current issues and controversies about magnesium?

Magnesium and blood pressure

Evidence suggests that magnesium may play an important role in regulating blood pressure. Diets that provide plenty of fruits and vegetables, which are good sources of potassium and magnesium, are consistently associated with lower blood pressure. The DASH study (Dietary Approaches to Stop Hypertension) suggested that high blood pressure could be significantly lowered by a diet high in magnesium, potassium, and calcium, and low in sodium and fat. In another study, the effect of various nutritional factors on incidence of high blood pressure was examined in over 30,000 U.S. male health professionals. After four years of follow-up, it was found that a greater magnesium intake was significantly associated with a lower risk of hypertension. The evidence is strong enough that the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure recommends maintaining an adequate magnesium intake as a positive lifestyle modification for preventing and managing high blood pressure.

Magnesium and heart disease

Magnesium deficiency can cause metabolic changes that may contribute to heart attacks and strokes. There is also evidence that low body stores of magnesium increase the risk of abnormal heart rhythms, which may increase the risk of complications associated with a heart attack. Population surveys have associated higher blood levels of magnesium with lower risk of coronary heart disease. In addition, dietary surveys have suggested that a higher magnesium intake is associated with a lower risk of stroke. Further studies are needed to understand the complex relationships between dietary magnesium intake, indicators of magnesium status, and heart disease.

Magnesium and osteoporosis

Magnesium deficiency may be a risk factor for postmenopausal osteoporosis. This may be due to the fact that magnesium deficiency alters calcium metabolism and the hormone that regulates calcium. Several studies have suggested that magnesium supplementation may improve bone mineral density, but researchers believe that further investigation on the role of magnesium in bone metabolism and osteoporosis is needed.

Magnesium and diabetes

Magnesium is important to carbohydrate metabolism. It may influence the release and activity of insulin, the hormone that helps control blood glucose levels. Elevated blood glucose levels increase the loss of magnesium in the urine, which in turn lowers blood levels of magnesium. This explains why low blood levels of magnesium (hypomagnesemia) are seen in poorly controlled type 1 and type 2 diabetes. In 1992, the American Diabetes Association issued a consensus statement that concluded: "Adequate dietary magnesium intake can generally be achieved by a nutritionally balanced meal plan as recommended by the American Diabetes Association." It recommended that "... only diabetic patients at high risk of hypomagnesemia should have total serum (blood) magnesium assessed, and such levels should be repleted (replaced) only if hypomagnesemia can be demonstrated".

What is the health risk of too much magnesium?

Dietary magnesium does not pose a health risk, however very high doses of magnesium supplements, which may be added to laxatives, can promote adverse effects such as diarrhea. Magnesium toxicity is more often associated with kidney failure, when the kidney loses the ability to remove excess magnesium. Very large doses of laxatives also have been associated with magnesium toxicity, even with normal kidney function. The elderly are at risk of magnesium toxicity because kidney function declines with age and they are more likely to take magnesium-containing laxatives and antacids. Signs of excess magnesium can be similar to magnesium deficiency and include mental status changes, nausea, diarrhea, appetite loss, muscle weakness, difficulty breathing, extremely low blood pressure, and irregular heartbeat. The Institute of Medicine of the National Academy of Sciences has established a tolerable upper intake level (UL) for supplementary magnesium for adolescents and adults at 350 mg daily. As intake increases above the UL, the risk of adverse effects increases.

Table of Food Sources of Magnesium

 Food

 Milligrams

%DV*

 100 percent Bran, 2 Tbs

44

11

 Avocado, Florida, 1/2 med

103

26

 Wheat germ, toasted, 1 oz

90

22

Almonds, dry roasted, 1 oz

86

21

Cereal, shredded wheat, 2 rectangular biscuits

80

20

Seeds, pumpkin, 1/2 oz

75

19

 Cashews, dry roasted, 1 oz

73

18

Nuts, mixed, dry roasted, 1 oz

66

17

Spinach, cooked, 1/2 c

65

16

 Bran flakes, 1/2 c

60

15

Cereal, oats, instant/fortified, cooked w/ water, 1 c

56

14

Potato, baked w/ skin, 1 med

55

14

 Soybeans, cooked, 1/2 c

54

14

 Peanuts, dry roasted, 1 oz

50

13

Peanut butter, 2 Tbs.

50

13

Chocolate bar, 1.45 oz

45

11

 Vegetarian baked beans, 1/2 c

40

10

Potato, baked w/out skin, 1 med

40

10

Avocado, California, 1/2 med

35

9

 Lentils, cooked, 1/2 c

35

9

Banana, raw, 1 medium

34

9

 Shrimp, mixed species, raw, 3 oz (12 large)

29

7

 Tahini, 2 Tbs

28

7

Raisins, golden seedless, 1/2 c packed

28

7

 Cocoa powder, unsweetened, 1 Tbs

27

7

 Bread, whole wheat, 1 slice

24

6

Spinach, raw, 1 c

24

6

 Kiwi fruit, raw, 1 med

23

6

 Hummus, 2 Tbs

20

5

 Broccoli, chopped, boiled, 1/2 c

19

5

*DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains very much of a specific nutrient. The DV for magnesium is 400 milligrams (mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving. Even foods that provide lower percentages of the DV will contribute to a healthful diet.

Selenium

Selenium: What is it?

Selenium is an essential trace mineral in the human body. This nutrient is an important part of antioxidant enzymes that protect cells against the effects of free radicals that are produced during normal oxygen metabolism. The body has developed defenses such as antioxidants to control levels of free radicals because they can damage cells and contribute to the development of some chronic diseases. Selenium is also essential for normal functioning of the immune system and thyroid gland.

What foods provide selenium?

Plant foods are the major dietary sources of selenium in most countries throughout the world. The amount of selenium in soil, which varies by region, determines the amount of selenium in the plant foods that are grown in that soil. Researchers know that soils in the high plains of northern Nebraska and the Dakotas have very high levels of selenium. People living in those regions generally have the highest selenium intakes in the United States. Soils in some parts of China and Russia have very low amounts of selenium and dietary selenium deficiency is often reported in those regions.
 

Selenium also can be found in some meats and seafood. Animals that eat grains or plants that were grown in selenium-rich soil have higher levels of selenium in their muscle. In the United States, meats and bread are common sources of dietary selenium. Some nuts, in particular Brazil nuts and walnuts, are also very good sources of selenium. The table of food sources of selenium suggests many dietary sources of selenium.

What is the Recommended Dietary Allowance for selenium for adults?

The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) individuals in each life-stage and gender group. The 2000 RDAs for selenium for adults , in micrograms (mcg), are:

Life-Stage

 Men

 Women

 Pregnancy

 Lactation

Ages 19 +

55 mcg

55 mcg

 

 

All ages

 

 

60 mcg

70 mcg

Results of the Total Diet Study, a national survey conducted by the U.S. Food and Drug Administration (1982-86), indicated that the diets of most adult men and women provide recommended amounts of selenium (10).

When can selenium deficiency occur?

Selenium deficiency is most commonly seen in parts of China where the selenium content in the soil, and therefore selenium intake, is very low. Selenium deficiency is linked to Keshan Disease. The most common signs of selenium deficiency seen in Keshan Disease are an enlarged heart and poor heart function. Keshan disease has been observed in low-selenium areas of China, where dietary intake is less than 19 mcg per day for men and less than 13 mcg per day for women. This intake is significantly lower than the current RDA for selenium.  Selenium deficiency also may affect thyroid function because selenium is essential for the synthesis of active thyroid hormone. Researchers also believe selenium deficiency may worsen the effects of iodine deficiency on thyroid function, and that adequate selenium nutritional status may help protect against some of the neurologic effects of iodine deficiency.


Selenium deficiency has been seen in people who rely on total parenteral nutrition (TPN) as their sole source of nutrition. TPN is a method of feeding nutrients through an intravenous (IV) line to people whose digestive systems do not function. Forms of nutrients that do not require digestion are dissolved in liquid and infused through the IV line. It is important for TPN solutions to provide selenium in order to prevent a deficiency. Physicians can monitor the selenium status of individuals receiving TPN to make sure they are receiving adequate amounts.  Severe gastrointestinal disorders may decrease the absorption of selenium, resulting in selenium depletion or deficiency. Gastrointestinal problems that impair selenium absorption usually affect absorption of other nutrients as well, and require routine monitoring of nutritional status so that physicians can recommend appropriate treatment.

 Who may need extra selenium?

Selenium supplementation is essential for anyone relying on TPN as the sole source of nutrition, and selenium supplementation has become routine during TPN administration since the relationship between selenium deficiency and TPN was discovered. Gastrointestinal disorders such as Crohn's disease can impair selenium absorption. Most cases of selenium depletion or deficiency are associated with severe gastrointestinal problems, such as in individuals who have had over half of their small intestines surgically removed. A physician, who will determine the need for selenium supplementation, should evaluate individuals who have gastrointestinal disease and depleted blood levels of selenium.

What are some current issues and controversies about selenium?

Selenium and cancer

Some studies indicate that mortality (death) from cancer, including lung, colorectal, and prostate cancers, is lower among people with higher selenium blood levels or intake. Also, the incidence of nonmelanoma skin cancer is significantly higher in areas of the United States with low soil selenium levels.


The effect of selenium supplementation on the recurrence of these types of skin cancers was studied in seven dermatology clinics in the US from 1983 through the early 1990s. Supplementation with 200 mcg selenium daily did not affect recurrence of skin cancer, but significantly reduced total mortality and mortality from cancers. In addition, incidence of prostate cancer, colorectal cancer, and lung cancer was lower in the group given selenium supplements.


However, not all studies have shown a relationship between selenium status and cancer. In 1982, over 60,000 participants of the Nurses Health Study with no history of cancer submitted toenail clippings for selenium analysis. Toenail analysis is thought to reflect selenium status over the previous year. After three and one-half years, researchers compared the toenail selenium levels of nurses with and without cancer. They did not find any apparent benefit of higher selenium levels.


Selenium and heart disease

Some population surveys have indicated an association between a lower antioxidant intake with a greater incidence of heart disease. Additional lines of evidence suggest that oxidative stress from free radicals may promote heart disease. For example, it is the oxidized form of low-density lipoproteins (LDL, often called "bad" cholesterol) that promotes plaque build-up in coronary arteries. Selenium is one of a group of antioxidants that may help limit the oxidation of LDL cholesterol and thereby help to prevent coronary artery disease. Currently there is insufficient evidence available to recommend selenium supplements for the prevention of coronary heart disease.

Selenium and arthritis

Surveys of patients with rheumatoid arthritis, a chronic disease that causes pain, stiffness, swelling, and loss of function in joints, have indicated that they have reduced selenium levels in their blood. In addition, some individuals with arthritis have a low selenium intake.  The body's immune system naturally makes free radicals that can help destroy invading organisms and damaged tissue, but that can also harm healthy tissue.  Selenium, as an antioxidant, may help control levels of free radicals and help to relieve symptoms of arthritis. Current findings are considered preliminary, and further research is needed before selenium supplements can be recommended for individuals with arthritis.

Selenium and HIV

HIV / AIDS related malabsorption can deplete levels of many nutrients. Selenium deficiency is commonly associated with HIV / AIDS, and has been associated with a high risk of death from this disease. Of 24 children with HIV who were observed for five years, those with low selenium levels died at a younger age, which may indicate faster disease progression. An examination of 125 HIV positive men and women also associated selenium deficiency with mortality. Researchers believe that selenium may be important in HIV disease because of its role in the immune system and as an antioxidant. Selenium also may be needed for the replication of the HIV virus, which could deplete host levels of selenium. Researchers are actively investigating the role of selenium in HIV / AIDS, and see a need for clinical trials that evaluate the effect of selenium supplementation on HIV disease progression.

What is the health risk of too much selenium?

There is a moderate to high health risk of too much selenium. High blood levels of selenium can result in a condition called selenosis. Symptoms include gastrointestinal upsets, hair loss, white blotchy nails, and mild nerve damage. Selenium toxicity is rare in the United States and the few reported cases have been associated with industrial accidents and a manufacturing error that led to an excessively high dose of selenium in a supplement. The Institute of Medicine has set a tolerable upper intake level for selenium at 400 micrograms per day for adults to prevent the risk of developing selenosis. "Tolerable upper intake levels represent the maximum intake of a nutrient that is likely to pose no risk of adverse health effects in almost al individuals in the general population".

Table of Food Sources of Selenium

The selenium content of foods varies according to the growing area. The following table lists the mean selenium content of foods identified in the Total Diet Study  and in the USDA data bank.

Food

Micrograms

% DV*

Brazil nuts, dried, unblanched, 1 oz

840

1200

Tuna, canned in oil, drained, 3 1/2 oz

78

111

Beef / calf liver, 3 oz

48

69

Cod, cooked, dry heat, 3 oz

40

57

Noodles, enriched, boiled, 1 c

35

50

Macaroni and cheese (box mix), 1 c

32

46

Turkey, breast, oven roasted, 3 1/2 oz

31

44

Macaroni,elbow, enriched, boiled, 1 c

30

43

Spaghetti w/ meat sauce, 1 c

25

36

Chicken, meat only, 1/2 breast

24

34

Beef chuck roast, lean only, oven roasted, 3 oz

23

33

Bread, enriched, whole wheat, 2 slices

20

29

Oatmeal, 1 c cooked

16

23

Egg, raw, whole, 1 large

15

21

Bread, enriched, white, 2 slices

14

20

Rice, enriched, long grain,cooked, 1 c

14

20

Cottage cheese, lowfat 2%, 1/2 c

11

16

Walnuts, black, dried, 1 oz

5

7

Cheddar cheese, 1 oz

4

6

*DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains very much of a specific nutrient. The DV for selenium is 70 micrograms (mcg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving. Even foods that provide lower percentages of the DV will contribute to a healthful diet.

*DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains very much of a specific nutrient. The DV for selenium is 70 micrograms (mcg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving.Even foods that provide lower percentages of the DV will contribute to a healthful diet.

Zinc: What is it?

Zinc is an essential mineral that is found in almost every cell. It stimulates the activity of approximately 100 enzymes, which are substances that promote biochemical reactions in your body. Zinc supports a healthy immune system, is needed for wound healing,  helps maintain your sense of taste and smell , and is needed for DNA synthesis. Zinc also supports normal growth and development during pregnancy, childhood, and adolescence.

What foods provide zinc?

Zinc is found in a wide variety of foods. Oysters contain more zinc per serving than any other food, but red meat and poultry provide the majority of zinc in the American diet. Other good food sources include beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products. Zinc absorption is greater from a diet high in animal protein than a diet rich in plant proteins. Phytates, which are found in whole grain breads, cereals, legumes and other products, can decrease zinc absorption.

What is the Recommended Dietary Allowance for zinc?

The latest recommendations for zinc intake are given in the new Dietary Reference Intakes developed by the Institute of Medicine. Dietary Reference Intakes (DRIs) is the umbrella term for a group of reference values used for planning and assessing nutrient intake for healthy people. The Recommended Dietary Allowance (RDA), one of the DRIs, is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals. For infants 0 to 6 months, the DRI is in the form of an Adequate Intake (AI), which is the mean intake of zinc in healthy, breastfed infants. The AI for zinc for infants from 0 through 6 months is 2.0 milligrams (mg) per day. The 2001 RDAs for zinc for infants 7 through 12 months, children and adults in mg per day are:

Table 1: Recommended Dietary Allowances for Zinc for
Infants over 7 months, Children, and Adults

Age

Infants and Children

Males

Females

 Pregnancy

 Lactation

7 months to 3 years

3 mg

 

 

 

 

4 to 8 years

5 mg

 

 

 

 

9 to 13 years

8 mg

 

 

 

 

14 to 18 years

 

11 mg

9 mg

13 mg

14 mg

19+

 

11 mg

8 mg

11 mg

12 mg

Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III 1988-91)  and the Continuing Survey of Food Intakes of Individuals (1994 CSFII)  indicated that most infants, children, and adults consume recommended amounts of zinc.

When can zinc deficiency occur?

Zinc deficiency most often occurs when zinc intake is inadequate or poorly absorbed, when there are increased losses of zinc from the body, or when the body’s requirement for zinc increases. Signs of zinc deficiency include growth retardation, hair loss, diarrhea, delayed sexual maturation and impotence, eye and skin lesions, and loss of appetite. There is also evidence that weight loss, delayed healing of wounds, taste abnormalities, and mental lethargy can occur. Since many of these symptoms are general and are associated with other medical conditions, do not assume they are due to a zinc deficiency. It is important to consult with a medical doctor about medical symptoms so that appropriate care can be given.

Who may need extra zinc?

There is no single laboratory test that adequately measures zinc nutritional status. Medical doctors who suspect a zinc deficiency will consider risk factors such as inadequate caloric intake, alcoholism, digestive diseases, and symptoms such as impaired growth in infants and children when determining a need for zinc supplementation. Vegetarians may need as much as 50% more zinc than non-vegetarians because of the lower absorption of zinc from plant foods, so it is very important for vegetarians to include good sources of zinc in their diet.

Maternal zinc deficiency can slow fetal growth. Zinc supplementation has improved growth rate in some children who demonstrate mild to moderate growth failure and who also have a zinc deficiency. Human milk does not provide recommended amounts of zinc for older infants between the ages of 7 months and 12 months, so breast-fed infants of this age should also consume age-appropriate foods containing zinc or be given formula containing zinc. Alternately, pediatricians may recommend supplemental zinc in this situation. Breastfeeding also may deplete maternal zinc stores because of the greater need for zinc during lactation. It is important for mothers who breast-feed to include good sources of zinc in their daily diet and for pregnant women to follow their doctor’s advice about taking vitamin and mineral supplements.  Low zinc status has been observed in 30% to 50% of alcoholics. Alcohol decreases the absorption of zinc and increases loss of zinc in urine. In addition, many alcoholics do not eat an acceptable variety or amount of food, so their dietary intake of zinc may be inadequate.

Diarrhea results in a loss of zinc. Individuals who have had gastrointestinal surgery or who have digestive disorders that result in malabsorption, including sprue, Crohn’s disease and short bowel syndrome, are at greater risk of a zinc deficiency. Individuals who experience chronic diarrhea should make sure they include sources of zinc in their daily diet (see selected table of food sources of zinc) and may benefit from zinc supplementation. A medical doctor can evaluate the need for a zinc supplement if diet alone fails to maintain normal zinc levels in these circumstances.

What are some current issues and controversies about zinc?

Zinc, infections, and wound healing

The immune system is adversely affected by even moderate degrees of zinc deficiency. Severe zinc deficiency depresses immune function. Zinc is required for the development and activation of T-lymphocytes, a kind of white blood cell that helps fight infection. When zinc supplements are given to individuals with low zinc levels, the numbers of T-cell lymphocytes circulating in the blood increase and the ability of lymphocytes to fight infection improves. Zinc supplements are often given to help heal skin ulcers or bed sores, but they do not increase rates of wound healing when zinc levels are normal.

Zinc and the common cold

The effect of zinc treatments on the severity or duration of cold symptoms is controversial. A study of over 100 employees of the Cleveland Clinic indicated that zinc lozenges decreased the duration of colds by one-half, although no differences were seen in how long fevers lasted or the level of muscle aches. Other researchers examined the effect of zinc supplements on cold duration and severity in over 400 randomized subjects. In their first study, a virus was used to induce cold symptoms. The duration of illness was significantly lower in the group receiving zinc gluconate lozenges (providing 13.3 mg zinc) but not in the group receiving zinc acetate lozenges (providing 5 or 11.5 mg zinc). None of the zinc preparations affected the severity of cold symptoms in the first 3 days of treatment. In the second study, which examined the effects of zinc supplements on duration and severity of natural colds, no differences were seen between individuals receiving zinc and those receiving a placebo (sugar pill). Recent research suggests that the effect of zinc may be influenced by the ability of the specific supplement formula to deliver zinc ions to the oral mucosa. Additional research is needed to determine whether zinc compounds have any effect on the common cold.

Zinc and iron absorption

Iron deficiency anemia is considered a serious public health problem in the world today. Iron fortification programs were developed to prevent this deficiency, and they have been credited with improving the iron status of millions of women, infants, and children. Some researchers have questioned the effect of iron fortification on absorption of other nutrients, including zinc. Fortification of foods with iron does not significantly affect zinc absorption. However, large amounts of iron in supplements (greater than 25 mg) may decrease zinc absorption, as can iron in solutions. Taking iron supplements between meals will help decrease its effect on zinc absorption.

What is the health risk of too much zinc?

Zinc toxicity has been seen in both acute and chronic forms. Intakes of 150 to 450 mg of zinc per day have been associated with low copper status, altered iron function, reduced immune function, and reduced levels of high-density lipoproteins (the good cholesterol). One case report cited severe nausea and vomiting within 30 minutes after the person ingested four grams of zinc gluconate (570 mg elemental zinc). In 2001 the National Academy of Sciences established tolerable upper levels (UL), the highest intake associated with no adverse health effects, for zinc for infants, children, and adults. The ULs do not apply to individuals who are receiving zinc for medical treatment, but it is important for such individuals to be under the care of a medical doctor who will monitor for adverse health effects. The 2001 Upper Levels for infants, children and adults are:

Table 2: Upper Levels for Zinc for Infants, Children, and Adults

Age

Infants and Children

Males and Females

 Pregnancy and  Lactation

0 to 6 months

4 mg

 

 

 

 

7 to 12 months

5 mg

 

 

 

 

1 to 3 years

7 mg

 

 

 

 

4 to 8 years

12 mg

 

 

 

 

9 to 13 years

23 mg

 

 

 

 

14 to 18 years

34 mg

 

 

34 mg

Ages 19+

 

40 mg

40 mg

Selected Food Sources of Zinc

As the table indicates, red meat, poultry, fortified breakfast cereal, some seafood, whole grains, dry beans, and nuts provide zinc. Fortified foods including breakfast cereals make it easier to consume the RDA for zinc, however they also make it easier to consume too much zinc, especially if supplemental zinc is being taken. Anyone considering taking a zinc supplement should first consider whether their needs could be met by dietary zinc sources and from fortified foods.

Table 3: Selected Food Sources of Zinc

Food

 Milligrams

%DV*

Oysters, battered and fried, 6 medium

 16.0

100

Ready-to-Eat (RTE) Breakfast cereal, fortified with 100% of the DV for zinc per serving, 3/4 c serving

 15.0

100

Beef shank, lean only, cooked 3 oz

8.9

60

Beef chuck, arm pot roast, lean only, cooked, 3 oz

7.4

50

Beef tenderloin, lean only, cooked, 3 oz

4.8

30

Pork shoulder, arm picnic, lean only, cooked, 3 oz

4.2

30

Beef, eye of round, lean only, cooked, 3 oz

4.0

25

RTE Breakfast cereal, fortified with 25% of the DV for zinc per serving, 3/4 c

3.8

25

RTE Breakfast cereal, complete wheat bran flakes, 3/4 c serving

3.7

25

Chicken leg, meat only, roasted, 1 leg

2.7

20

Pork tenderloin, lean only, cooked, 3 oz

2.5

15

Pork loin, sirloin roast, lean only, cooked, 3 oz

2.2

15

Yogurt, plain, low fat, 1 c

2.2

15

Baked beans, canned, with pork, 1/2 c

1.8

10

Baked beans, canned, plain or vegetarian, 1/2 c

1.7

10

Cashews, dry roasted w/out salt, 1 oz

1.6

10

Yogurt, fruit, low fat, 1 c

1.6

10

Pecans, dry roasted w/out salt, 1 oz

1.4

10

Raisin bran, 3/4 c

1.3

8

Chickpeas, mature seeds, canned, 1/2 c

1.3

8

Mixed nuts, dry roasted w/peanuts, w/out salt, 1 oz

1.1

8

Cheese, Swiss, 1 oz

1.1

8

Almonds, dry roasted, w/out salt, 1 oz

1.0

6

Walnuts, black, dried, 1 oz

1.0

6

Milk, fluid, any kind, 1 c

.9

6

Chicken breast, meat only, roasted, 1/2 breast with bone and skin removed

0.9

6

Cheese, cheddar, 1 oz

0.9

6

Cheese, mozzarella, part skim, low moisture, 1 oz

0.9

6

Beans, kidney, California red, cooked, 1/2 c

0.8

6

Peas, green, frozen, boiled, 1/2 c

0.8

6

Oatmeal, instant, low sodium, 1 packet

0.8

6

Flounder/sole, cooked, 3 oz

0.5

4

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains very much of a specific nutrient. The DV for zinc is 15 milligrams (mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided in one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet.

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