Vitamin A to Zinc

 

Course Objectives

By completing this course the healthcare professional will be able to:                             

• Define and distinguish between the various categories of vitamins and dietary supplements.
• Identify foods that provide vitamins.
• Describe the signs and symptoms associated with vitamin deficiencies.
• Identify the daily recommended amounts for a balanced diet.
• Identify issues and controversy surrounding vitamin supplements.

 

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 o