Skip to content. | Skip to navigation

Personal tools


You are here: Home / Media Resources / Articles / Do Vitamins Work?

Do Vitamins Work?

This article takes a fairly in depth look at the effectiveness and use of vitamins. It was sourced from 'howstuffworks'.

Vitamins In-Depth

Vitamins do not share a common chemistry, but they do share certain characteristics. They are all organic nutrients that are necessary in small amounts for normal metabolism and good health. Your diet or supplements provide most vitamins. The body can manufacture only three vitamins (D, K, and the B vitamin biotin) from nondietary sources. Unlike carbohydrates, fats, and proteins, vitamins are not sources of energy. Instead, vitamins are chemical partners for the enzymes involved in the body's metabolism, cell production, tissue repair, and other vital processes.

Vitamins are either fat soluble or water soluble. The fat-soluble vitamins, which include A, D, E, and K, are absorbed by the body using processes that closely parallel the absorption of fat. They are stored in the liver and used up by the body very slowly. The water-soluble vitamins include C and the B complex vitamins. The body uses these vitamins very quickly. Excess amounts are eliminated in urine.

Guidelines for Vitamin Adequate Intake

The Recommended Daily Allowance (RDA) for vitamins, set by the Food and Nutrition Board of the National Academy of Sciences-National Research Council, has been used for years as a guide for determining the amount of vitamins needed for a healthy diet. The RDA refers to an estimate of the average daily requirement. It is not completely adequate, however, for informing people about the amounts of vitamins they may need.

The RDA is gradually being enhanced using a new standard called the Dietary Reference Intake (DRI). The DRI is based on the following ratings, which will eventually appear on labels:

  • The recommended daily allowance (RDA). This is the current rating on most vitamins.
  • The estimated average requirement (EAR). This is the amount adequate for 50% of all people, which will be put on labels when it can be calculated.
  • Adequate intake (AI). This is an amount that will be used if there is insufficient data to calculate the EAR.
  • Tolerable upper intake level (UL). This is the maximum dose likely to be safe in nearly all individuals. It will be included on labels if this amount is known.

Food and supplement labels now typically list the Daily Value (DV). This is the percentage of the amount of a nutrient that experts believe a person needs in their daily diet. On food labels it is usually based on one serving size for a person who takes in 2,000 calories a day.

Regulating Quality

Regulation of dietary supplements by the U.S. Food and Drug Administration (FDA) is a complex issue.

Labels on vitamins and other dietary supplements now include nutrient information and list all ingredients, including identifying parts of plants from which ingredients may be taken. Unlike the labels for drugs, however, labels for vitamins and supplements may not claim to prevent or treat any specific disease. Labels for vitamins and supplements include one of the following:

  • Health claim -- description of how the substance may reduce the risk of a health-related condition
  • Nutrient claim -- description of the amount of the nutrient in the product or
  • Structure or function claim -- description of how the product may affect organs or systems of the body, without claiming to prevent or treat specific disease

The quality of dietary supplements depends on the manufacturer and is not ensured by FDA. The US government does not require that supplements be standardized, meaning that the amounts or quality of nutrients may vary depending on the batch. So, more expensive supplements are not necessarily better than the less expensive ones. Government regulations are in the process of catching up to the boom in the supplement industry. In the meantime, some companies voluntarily adhere to rigorous quality controls, while others do not.

The US Pharmacopeia, an independent organization that sets quality standards for drugs, has also implemented standards for vitamins. Consumers may look for the USP label on products of companies that adhere to these standards. USP verification means the following:

  • What is in the bottle matches what is listed on the label.
  • There are no harmful levels of contaminants.
  • The supplement will be absorbed properly into the body.
  • It has been produced according to good manufacturing standards.

Before selling any supplement introduced after 1994, manufacturers must submit information as to why the product is considered safe for people. The FDA may refuse to allow it on the market if it finds the evidence insufficient. The FDA does not require manufacturers to provide any scientific evidence that dietary supplements are safe and effective before a product is sold (unlike drugs, which must be proven both safe and effective through clinical trials). If a supplement causes side effects in people once it is for sale, the government may place restrictions on the supplement or withdraw it from the market. The FDA may also withdraw products from the market if their labels are misleading or false.

People Who Should Take Vitamin Supplements

About 30% of Americans take at least one vitamin or mineral supplement daily. In a large study that examined the death rates of 11,000 people, however, there was no difference in mortality rate between those who took vitamin supplements and those who didn't. If a diet is healthy, most people do not need vitamins, but there are some exceptions. Nevertheless, a number of experts do recommend that adults take a multivitamin every day.

Pregnant and Breast-Feeding Women. Women who are pregnant or who are breast-feeding generally need additional vitamins. The B vitamins are particularly important. Women who are vegetarians must be sure to avoid deficiencies, which can harm their offspring. Folic acid reduces the risk for neural tube defects and possibly facial abnormalities, such as cleft palate. Multivitamins that contain folic acid also appear to be somewhat protective. Taking extra folic acid plus multivitamin supplements (which have additional benefits) and starting them before a woman actually becomes pregnant is the optimal approach.

The human body stores several years' worth of vitamin B12, so nutritional deficiency of this vitamin is extremely rare. Although, people who follow a strict vegetarian diet and do not consume eggs or dairy products may require vitamin B12 supplements.

Folate levels from even healthy diets may not be protective enough for pregnant women and supplements are needed. Requirements are as follows:

  • The RDA for folic acid prior to conception and during pregnancy is 400 mcg.
  • During breast feeding between 260 and 280 mcg is recommended.

The following vitamins may have some value for pregnant women:

  • Choline, another vitamin B, is also essential for pregnant (450 mg) and nursing women (550 mg).
  • Vitamin B6 may help improve morning sickness.
  • One study also suggested that if pregnant women took vitamin K supplements, their infants might not need the required injection of this vitamin after birth, but supplements of vitamin K during pregnancy are not currently recommended.

Some women have low vitamin A reserves in their liver. It is important to note, however, that too much vitamin A significantly increases the risk for birth defects. Daily amounts of 10,000 IU of vitamin A in supplements and food (an amount not far above the RDA level) can pose a danger. Experts recommend that pregnant women take in no more than 8,000 IU per day and avoid eating liver.

Infants and Children. Infants who are breastfed by healthy mothers receive enough vitamins except, in some cases, vitamins K and D. Human milk has low levels of K, and the newborn's immature intestinal tract may not produce enough of the baby's own supply. Most babies are given an injection of this vitamin at birth. Infants being breastfed by malnourished women or those who lack sufficient exposure to sunlight may be deficient in vitamin D. In these cases, supplements of 200 - 300 IU are recommended. Formulas are required to contain sufficient vitamins and minerals. One study suggests that vitamin supplements for infants under 1 year of age may help protect them from developing type 1 diabetes later on. Beyond infancy, most American children receive all the vitamins they need from their diet unless they are living in severely deprived circumstances.

Smokers. Smoking interferes with absorption of several vitamins, importantly vitamin C. In fact, in one study nearly 25% of female smokers and 31% of male smokers were deficient in vitamin C. Folic acid supplements may be important for all smokers. Taking high doses of antioxidant vitamins, however, may actually be harmful in smokers, especially beta carotene. Instead of taking supplements, most smokers should be sure their diets are rich in fresh fruits and vegetables and whole grains.

Alcoholics. Alcoholics often suffer from multiple vitamin deficiencies. The most dangerous deficiencies are from vitamins B1 (thiamin), folic acid, B6 (pyridoxine), B2 (riboflavin), and vitamin C.

Dieters and Vegetarians. People on weight-reduction diets with less than 1,000 calories a day should probably take a multivitamin and should also check regularly with a physician.

Vegetarians may need riboflavin, vitamin B12, and vitamin D supplements. Vegans, who do not eat dairy or eggs as well as meat, may be at further risk for vitamin A deficiencies if they do not also have plenty of dark colored fruits and vegetables. Those who eat eggs and dairy products need only watch their iron levels.

Deficiencies in vegetarian children may be particularly harmful. (One study, for example, reported that adolescents who had been on macrobiotic diets before age 6 and were deficient in vitamin B12 scored lower on psychologic tests.) Pregnant and breast-feeding women who are vegetarians must be sure to have sufficient vitamins. Of special note, maternal deficiencies in vitamin B12 may cause delayed growth and neurologic problems in their newborns.

Older Adults. Deficiencies of vitamins and important minerals have been observed in almost a third of elderly people. Often their dietary habits slip and they fail to eat balanced meals regularly. Multiple drug regimens may prevent absorption of some vitamins. Elderly people, particularly if they are not exposed to sunlight, may be deficient in vitamin D. They also may have low levels of important B vitamins. (Older adults showing signs of dementia should be checked for B12 deficiencies as well as other disorders causing mental disturbances.) One study reported that the immune systems of elderly people may benefit from higher levels of vitamin E than the daily recommended dosage. It should be noted, however, that metabolism slows down as a person ages, and in elderly people it takes the liver longer to eliminate drugs and vitamins from the body. The effect of some vitamin supplements, therefore, may be intensified. Dosage levels of vitamin A, for instance, which might be harmless in a younger adult, could be toxic in an elderly patient. Nevertheless, experts are increasingly recommending extra vitamin and mineral supplements for older people.

People Who Need to Avoid Sunlight. People who need to avoid sunlight and whose diet is low in foods that contain vitamin D should take supplements. People with darker skin are at higher risk for deficiencies than those with whiter skin. (Note: vitamin D is toxic in high doses, and no one should exceed the recommended daily intake of vitamin D except under the direction of a physician.)

Vitamin A and Provitamin A Carotenoids (E.g., Beta Carotene)


Essential for growth, bone development, night vision, reproduction, and healthy skin.

Recommended daily allowance (RDA) or dietary reference intake (DRI)

(mcg = micrograms, mg = milligrams, IU = international units)

Vitamin A RDA and Upper Limit (when toxicity is risk) are the following:

For children: 1,000 IU ages one to three (upper limit is 2,000 IU); 1,333 IU ages 4 - 8 (upper limit is 3,000 IU); and 2,000 IU for 9 - 13 (upper limit is 5,665 IU).

For nonpregnant women: 2,330 IU ages 14 through adulthood. (Upper limit is 9,335 IU for ages 14 - 18 and 10,000 IU for women over 19.)

For pregnant women: 2,500 IU for pregnant women under 18; 2,565 IU for pregnant women over 19. (Upper limit is 9,335 IU for ages 14 - 18 and 10,000 IU for women over 19. It should be noted that some experts recommend 8,000 IU as the upper limit during pregnancy.)

For nursing women: 4,000 IU for nursing mothers under 18; 4,335 IU for nursing mothers over 19. (Upper limit is 9,335 IU for ages 14 - 18 and 10,000 IU for women over 19.)

For men: 3,000 IU ages 14 - 18; 3,000 IU for ages 19 and above. (Upper limit is 10,000 IU.)

Note: In determining the daily vitamin A allowance, experts also take note of provitamins, such beta carotene, that convert to vitamin A. Some experts recommend 3 - 6 mg of beta-carotene.

Vitamin A is also now being measured with a new unit called the Retinol Activity Equivalent (RAE or RE). One RE is equal to 1 mcg. Retinol is the most active form of vitamin A and it is also converted in the liver from carotenoids. One RE is equal to 12 mcg of beta-carotene or 24 mcg of alpha-carotene or beta-cryptoxanthin).

Foods containing the vitamin

Animal products, such as liver, dairy products, eggs, and fish liver oil. Provitamin A carotenoids are also found in dark red, green, and yellow vegetables. Requires some dietary fat to be absorbed.

Effects of deficiencies

Skin disorders and eye damage. In less developed countries severe deficiencies cause blindness in 250,000 children each year. Diets low in vitamin A may also increase the risk of developing cancer. Low dietary intake of vitamin A has been associated with impaired lung function in children.

People at risk for deficiencies

Preschool children and any child with inadequate intake of protein, calories, and zinc. Iron deficiency may also impair metabolism of vitamin A.

People with serious disorders in the intestine, liver or pancreas, such as cystic fibrosis, steatorrhea, biliary obstruction, cirrhosis, and others.

Vegans (vegetarians who do not eat eggs and dairy). Such individuals should be sure to have plenty of deep-colored fruits and vegetables.

People who abuse alcohol. It should be noted, however, that people with alcoholism may be at risk for vitamin A deficiency, but a combination of high-dose vitamin A and alcohol may cause toxic effects in the liver.

Healthy adults usually have a year's store of vitamin A in the liver, so temporary nutritional deficiencies or problems with fat absorption are unlikely to cause serious vitamin A deficiency problems.


Very toxic when taken in high-dose supplements for long periods of time.

Symptoms of overdose include dizziness, nausea, vomiting, headache, skin damage, mental disturbances, and, in women, infrequent periods.

Can affect almost every part of the body, including eyes, bones, blood, skin, central nervous system, liver, and genital and urinary tracts. Severe toxicity can cause blindness and may even be life threatening. In children, chronic overdose can cause fluid on the brain and as well as adult complications. High consumption of vitamin A may also increase the risk of gastric cancer and the risk of osteoporosis and fractures in both men and women.

Pregnant women who take amounts not much higher than RDA levels increase the risk for birth defects in their children. Liver damage can occur in children who take RDA-approved adult levels over prolonged periods of time or in adults who take as little as five times the RDA-approved amount for 7 - 10 years.



B Vitamins: General Information

Vitamin B1 (thiamin)


The B vitamins have a wide and varied range of functions in the human body. Most B vitamins are involved in the process of converting blood sugar into energy.

Essential for converting blood sugar into energy and is involved in metabolic activities in nerves, heart, and muscles and in the production of red blood cells.

Recommended daily allowance (RDA) or dietary reference intake (DRI)

(mcg = micrograms, mg = milligrams, IU = international units)


RDA is 1.2 mg per day for men and 1.1 mg for women.

Foods containing the vitamin


Best source is pork and good sources are dried fortified cereals, oatmeal, corn, nuts, cauliflower, and sunflower seeds. Supplements for people with normal diets and health are unnecessary.

Effects of deficiencies

Deficiencies are uncommon in the US, but when they occur, they usually involve several B vitamins, since many of them come from the same food groups.

Severe vitamin B1 deficiency is known as beriberi. Can cause visual disturbances, paralysis, staggering, loss of sensation in the legs and feet, psychosis, and congestive heart failure.

People at risk for deficiencies

Alcohol interferes with these vitamins, and some of the physical and mental problems that alcoholics experience may be attributed to a deficiency of B vitamins. Elderly people are also at risk for deficiencies because of inadequate diets and potential interference with B-vitamin absorption by medications. Deficiencies can occur in severely malnourished people or in those receiving long-term dialysis or intravenous feeding. Vegetarians may be at risk.

See general vitamin B description.


Because the B vitamins are water-soluble and eliminated in the urine, toxic reactions from oral administration of most of them are extremely rare. (Exceptions are niacin and B6.) It should be noted that substances known as B15 (pangamic acid) and B17 (laetrile) are neither vitamins nor nutrients; both chemicals are highly dangerous and have no proven nutritional or health value.

No toxic effects have been reported from thiamin.


B Vitamins

Vitamin B2 (riboflavin)

Vitamin B3 (niacin) also known as nicotinic acid

Vitamin B5 (Pantothenic Acid)


Important in the production of energy.

Helps break down blood sugar for energy. Acts as a vasodilator, widening blood vessels and increasing blood flow. May be prescribed for improving cholesterol levels.

Important for metabolism of fats, carbohydrates, and proteins, as well as production of steroid hormones and other important chemicals.

Recommended daily allowance (RDA) or dietary reference intake (DRI)

(mcg = micrograms, mg = milligrams, IU = international units)

DRI is 1.7 mg.

DRI is 20 mg.

Adequate intake (AI) is 4 - 7 mg.

Foods containing the vitamin

Liver, dried fortified cereals, dairy products, fish. Some dark green vegetables. Supplements for people with normal diets and health are unnecessary.

Mackerel, swordfish, chicken, veal, dried fortified cereals, pork, salmon, and beef liver. Supplements are unnecessary in people with normal health and diets.

Whole grains, beans, milk, eggs, and liver. Supplements are unnecessary in people with normal health and diets.

Effects of deficiencies

Deficiencies affect the skin and mucous membranes and can cause cracks on the lips or corners of the mouth, eczema of the face and genitals, a burning sensation on the tongue, eye irritation. May contribute to anemia when iron levels are low and contribute to elevated levels of homocysteine, a heart risk factor.

Deficiency causes pellagra; symptoms can include eczema, intestinal and stomach distress, depression, headache, thinning of the hair, and excess saliva production.

Deficiency is unlikely except in company with other B vitamin deficiencies. Symptoms include abdominal distress, burning sensation in the heels, and sleep problems.

People at risk for deficiencies

See general vitamin B description.

Alcoholics and any malnourished persons.

Alcoholics and any malnourished persons.


Until recently, no toxic effects had been reported even from large doses of riboflavin. However, one study indicated that high consumption of vitamin B2 might increase the risk of stomach cancer. More research is needed. (In the same study, vitamins B1, B3, and B6 were protective.)

Even mildly high doses of niacin can cause hot flushing of the face and shoulders, headache, itchiness, and stomach problems. Some report heart disturbances and temporarily lowered blood pressure. Large doses may produce ulcers, gout, diabetes, and liver damage, which are usually reversed when high doses are discontinued.

Although no toxicity has been reported in humans, high dosages have caused liver damage in rats.


B Vitamins

Vitamin B6 (pyridoxine)

Vitamin B12 (cobalamin)


Has an effect on over 60 proteins in the body, importantly, those that play a role in the nervous system, in red and white blood cell production, and in heart disease.

Essential for the production of blood cells, manufacturing genetic material, and for healthy functioning of the nervous system.

Recommended daily allowance (RDA) or dietary reference intake (DRI)

(mcg = micrograms, mg = milligrams, IU = international units)

RDA is 1.3 mg in adults under 50 and 1.7 mg for older men and 1.5 for older women. (Some experts recommend 3 to 6 mg for people who need heart protection.) Upper limit is 100 mg for adults.

RDA is 2.4 mcg in men and nonpregnant women, 2.6 mcg in pregnant women, and 2.8 mcg in nursing mothers.

Foods containing the vitamin

Meats, oily fish, poultry, whole grains, dried fortified cereals, soybeans, avocados, baked potatoes with skins, watermelon, plantains, bananas, peanuts, and brewer's yeast.

The only natural dietary sources are animal products, including meats, dairy products, eggs, and fish (clams and oily fish are very high in B12). Like other B vitamins, however, B12 is added to commercial dried cereals.

Effects of deficiencies

Increased levels of homocysteine, associated with heart disease and possibly Alzheimer's disease. Skin problems and nervous system disorders, including impaired memory and concentration. Increased risk for kidney stones.

Note: People who have been taking more than 50 mg for some time and stop suddenly are at risk for a so-called rebound deficiency. When people stop, they should taper off slowly.

Deficiencies elevate homocysteine, a possible risk factor for heart disease and Alzheimer's disease.

May cause severe depression, memory loss, instability, disorientation, and decreased reflexes, and possibly hearing loss.

Children who are deficient may experience growth failure. Deficiencies in pregnant and breast-feeding women may cause neurologic harm in their offspring.

A genetic defect that causes vitamin B12 deficiencies is responsible for pernicious anemia, a serious disorder, which must be treated with injections of vitamin B12 or else neurologic damage may occur.

People at risk for deficiencies

Alcoholics and any malnourished person. In rare cases, infants are born unable to metabolize pyridoxine; in such cases, seizures or convulsions can occur and vitamin B6 must be administered.

Alcoholics and any malnourished persons. Evidence suggests deficiencies may be caused by Helicobacter pylori (H. pylori) bacteria (a cause of ulcers). The elderly may have trouble absorbing natural vitamin B12 and require supplements. Vegetarians are at higher risk for deficiencies.


Very high doses can cause nerve damage with symptoms of instability and numbness in the feet and hands, which may be permanent in some cases. Of specific concern are possible adverse effects on nerve development in the offspring of pregnant women who take large doses, such as for morning sickness. Pyridoxine also reduces the effects of L-dopa, the drug used for Parkinson's disease.

There is no evidence of toxicity with this vitamin.


B Vitamins

Biotin (a B vitamin)

Choline (a B vitamin)

Folate, or Folic Acid, its synthetic form (a B vitamin)


Involved in the production of amino acid proteins and fatty acids.

Essential for fetal brain development and for learning and memory.

Important for many metabolic processes in the body. It is used in the manufacturing of neurotransmitters (chemical messengers in the brain), in protecting the heart, and for synthesizing genetic materials (DNA) in the cells. It may improve blood flow.

Recommended daily allowance (RDA) or dietary reference intake (DRI)

(mcg = micrograms, mg = milligrams, IU = international units)

There is no DRI for biotin; some experts suggest 30-100 mcg.

RDA 425 mg for nonpregnant women, 450 mg for pregnant women, and 550 mg for nursing women.

Supplements may be folate (natural) or folic acid (synthetic). Folic acid is nearly twice the potency of folate.

DRI is 400 mcg (.4 mg) of folate for the general population.

Some experts recommend 400 mcg of folic acid for heart protection; although one study suggested 800 mcg (.8 mg) a day is necessary to reduce homocysteine levels.

Women who are planning to be pregnant should certainly take 400 mcg of folic acid before conception, during pregnancy, and while nursing.

Foods containing the vitamin

Dietary sources are eggs, milk, liver, mushrooms, bananas, tomatoes, whole grains, nuts, and brewer's yeast. Also produced by bacteria in the intestines.

Peanuts, eggs, cauliflower, and meats, especially liver.

Avocado, bananas, orange juice, cold cereal, asparagus, fruits, green leafy vegetables, dried beans and peas, and yeast. Folic acid supplements are now added to commercial grain products.

Effects of deficiencies

Deficiencies are almost unheard of.

Low levels during pregnancy increase risk of birth defects in newborns.

As with vitamins B6 and B12, deficiencies elevate homocysteine, which may increase the risk for heart disease, and possibly Alzheimer's disease. Low levels during pregnancy increase risk of birth defects in newborns. Deficiencies can also cause depression and megaloblastic anemia and impair concentration, memory, and hearing.

People at risk for deficiencies



Alcoholics, malnourished persons, people with conditions that disturb the small intestine, people taking certain drugs, particularly methotrexate. Other risk factors for deficiency: high-dose aspirin, smoking, treatment for seizures, taking oral contraceptives.



Excessive doses can cause intestinal problems, and there is also some concern that high doses can be carcinogenic.

Low potential for toxicity. Some link between high doses and central nervous system disorders, zinc deficiency, and seizures in epileptics. This risk appears to be low, but results indicate that megadoses should be avoided. High amounts in the elderly may mask symptoms of vitamin B12 deficiencies.


Vitamin C (Ascorbic Acid)


Vitamin C is a water-soluble vitamin. Acts as an antioxidant (reduces harm from damaging chemical processes in the body). Essential for the production of collagen, the basic protein in bones, cartilage, tendons, and ligaments. May help boost the immune system.

Recommended daily allowance (RDA) or dietary reference intake (DRI)

(mcg = micrograms, mg = milligrams, IU = international units)

DRI is 75 mg (women) and 90 mg (men). (Smokers need an additional 35 mg.)

Foods containing the vitamin

Citrus fruits and juices, papayas, hot chili peppers, bell peppers, broccoli, potatoes, kale, red cabbage, cauliflower, cantaloupe, sweet potatoes, and Brussels sprouts. Note: Orange juice is the most important source of vitamin C in the US, with frozen juice being the best source of the vitamin.

Effects of deficiencies

Scurvy is the primary deficiency disease. Affects most body tissues, particularly bones, teeth, and blood vessels. Early symptoms include tiredness, weakness, irritability, weight loss, and vague muscle aches. Later symptoms are bleeding gums, wounds that won't heal, rough skin, and wasting away of the muscles. Deficiencies may contribute to periodontal disease and gallstones. Low dietary intake of vitamin C has been associated with impaired lung function in children. Low intake may also increase lead levels in the blood.

People at risk for deficiencies

Deficiency has been uncommon in the US, usually occurring in the elderly, alcoholics, cancer patients, and some food faddists. Surprisingly, however, studies now suggest that as many as 16% of middle-aged Americans, with the highest risk in smokers and middle aged men, are deficient in vitamin C. High doses of aspirin taken over a long period of time can interfere with vitamin C.


Tolerable upper limit is 2000 mg/day. High doses may cause headaches and diarrhea. Long-term high doses may increase risk for kidney stones. Ascorbic acid increases iron absorption so people with blood disorders, such as hemochromatosis, thalassemia, or sideroblastic anemia, should avoid high doses. Large doses may also thin blood and interfere with anticoagulant medications, blood tests used in diabetes, and stool tests. Rebound scurvy can occur after abrupt withdrawal from long-term large doses. This may affect infants or pregnant women who withdraw suddenly from high doses.


Vitamin D


Vitamin D is actually a single term for several hormones that are stored mainly in the liver and also in fat and muscle tissue. It is essential for the absorption of calcium into the bone and for normal bone growth.

Recommended daily allowance (RDA) or dietary reference intake (DRI)

(mcg = micrograms, mg = milligrams, IU = international units)

RDA is 200 IU (5 mcg) per day for children and most adults, 400 IU (10 mcg) for people between ages 50 and 60, and 600 IU (15 mcg) for those over 70 who do not have sufficient exposure to sunlight. breastfed infants may need supplements.

How the Body Obtains the vitamin

Manufactured in the body from a chemical reaction to the ultraviolet radiation in sunlight. It is found in a few food sources, including vitamin D fortified milk, fatty fish, egg yolk, and liver. Note: some milk products (such as yogurt and skim milk) may have little vitamin D.

Effects of deficiencies

Softening of the bones caused by low amounts of calcium and phosphorous (called rickets in children and osteomalacia in adults). Also increases the risk for hip fractures in postmenopausal women. Associated with a higher risk for prostate cancer and breast cancer risk.

Muscle disease.

People at risk for deficiencies

Older people, particularly if they live in the North, who are underexposed to sunlight. Obesity may also increase risk. There is some concern, in fact, that vitamin D deficiency may be a growing problem in the US among younger adults as sunscreen use becomes widespread. Individuals at highest risk for vitamin D deficiency are those who assiduously avoid the midday sun, wear protective clothing, regularly use sunscreen, and have dark skin. Exposure to sunlight for about 15 to 20 minutes at mid-morning or mid-afternoon three times a week is recommended for most people who live in temperate climates.


Vitamin D is very toxic in high doses. In infants, daily amounts higher than 1000 IU can cause mental and growth retardation, kidney failure, and death. In children and adults, daily amounts over 50,000 IU can cause weakness, anorexia, vomiting, diarrhea, and mental changes. Prolonged use of megadoses can cause calcification of soft tissue and life-threatening kidney failure. Low-calcium diets and withdrawal from the vitamin can usually reverse the side effects except for kidney failure.



Vitamin E (Tocopherol or Tocotrienol)

Vitamin K


A fat-soluble antioxidant vitamin that helps prevent cell membrane damage and may inhibit oxidation of LDL cholesterol (a process that increases its harmful effects on arteries). People at high risk of heart problems, such as some diabetics, may reduce their risk of heart attacks and heart disease by taking vitamin E. Further study is underway to confirm initial research published in 2004. One 2005 study found that vitamin E may protect against Parkinson’s Disease.

The most important function of vitamin K is its role in blood clotting and prevention of bleeding. The vitamin also contributes to maintaining healthy bones and healing fractures.

Recommended daily allowance (RDA) or dietary reference intake (DRI)

(mcg = micrograms, mg = milligrams, IU = international units)

RDA is 15 mg (22 IU) for all adults, including pregnancy women. 19 mg (28 IU) for nursing mothers. (Supplements should be taken along with some oil or fat to be absorbed.)

Vitamin E is composed of 8 compounds (four tocopherols and four tocotrienols). Vitamin E is most often available as supplements of dl alpha tocopherol (a synthetic form).

Other vitamin E compounds may prove to be more active than the standard synthetic supplement. They include natural vitamin E, called d-alpha- or RRR-alpha-tocopherol succinate (VES). Other vitamin E compounds of interest are tocotrienol and beta and gamma tocopherol. Supplements that contain a combination of some of these forms may be most beneficial.

RDA is 60 to 65 micrograms (women) and 70 to 80 micrograms (men).

Foods containing the vitamin

Vegetable oils (particularly wheat germ oil), sweet potatoes, turnip greens, mangos, avocados, nuts, sunflower seeds, and soybeans.

Tocotrienol (a possibly beneficial form) is found in natural tropical oils. Palm oil sold in the US is refined and does not contain tocotrienol.

Best dietary sources are canola oil, cruciferous vegetables, and soybean oil. Good sources are beef liver, bran, and olive oil.

Also produced by bacteria in the intestines.

Effects of deficiencies

Deficiencies have not been established.

Easy bruising, bleeding. May increase the risk of hip fractures in women.

People at risk for deficiencies

Low-birth weight infants.

People with medical problems that impair fat absorption, such as Crohn's disease, cystic fibrosis, steatorrhea, liver diseases (such as cirrhosis).

People with abetalipoproteinemia, a rare genetic disorder that impairs fat metabolism.

Deficiency may occur in patients who have problems absorbing fats, such as those with cirrhosis, people who are on long-term antibiotic therapy, or who are taking other medications, including cholestyramine, Dilantin, and phenobarbital. Some evidence suggests that more young people may be deficient than previously believed.


Upper level recommended is 1,500 IU of alpha tocopherol. Large doses may cause bleeding problems, particularly in people taking anti-clotting medications. Some research now indicates that vitamin E, like other antioxidants, may have pro-oxidant and damaging effects. Although vitamin E is one of the best studied vitamins, research has yielded conflicting results, and definitive conclusions about the benefits and toxicity of vitamin E have not yet been determined. In a major 2005 study, there was no significant difference in cancer rates between people who took 400 IU of vitamin E daily and those who did not, although those who took the supplement had a higher risk of heart failure. Additional studies also link high levels of vitamin E with a slightly increased risk of heart failure and death. On the other hand, studies show that vitamin E may reduce heart problems in high-risk patients such as certain diabetics.

Allergic-type responses, including rash and itching, to high doses have been reported. Those who are taking Coumadin, an anticoagulant, should not take vitamin K without cons



Carotenoids are a group of more than 700 fat soluble nutrients that produce the colors in foods such as carrots, pumpkins, sweet potatoes, tomatoes, and other deep green, yellow, orange, and red fruits and vegetables. Many are proving to be very important for health. Beta carotene is the most widely studied carotenoid, but others are proving to be of great interest. As with some, but not all, carotenoids, beta carotene is known as a provitamin A because it converts to the vitamin in the body.

They are categorized as either xanthophylls or carotenes according to their chemical composition.


Carotenes are hydrocarbons and most are found in yellow, orange, and red vegetables. They include beta and alpha carotene and lycopene.

  • Beta Carotene and other Provitamin A Carotenoids. Beta carotene, alpha-carotene, and beta-cryptoxanthin are carotenes that are converted into vitamin A or retinol (the active form of vitamin A) in the body. They are found in many yellow fruits and vegetables. Beta carotene is the most widely studied carotenoid. Evidence now strongly suggests that when taken as a separate supplement it can have harmful effects.
  • Lycopene. Lycopene is responsible for the red color in fruits and vegetables, including tomatoes, red grapes, watermelon, and pink grapefruit. It is also found in papayas and apricots. It does not convert to vitamin A but may have important cancer fighting properties and other health benefits.
  • The beneficial actions of most carotenes such as those tomatoes, corn, and carrots, appear to be enhanced by cooking them, especially in oil (preferably olive, canola, or another monounsaturated oil). (Note: Cooking can also destroy certain nutrients, such as vitamin C, in these vegetables.)


Xanthophylls contain oxygen and most are found in green vegetables, such as broccoli, cabbage, and kale. They are also in yellow fruits and vegetables. Xanthophylls include lutein and zeaxanthin, which are both stored in the retina of the eye. Neither converts to vitamin A. Both are powerful antioxidants and may be very important for healthy eyes. Unlike carotenes, cooking may reduce the antioxidant activity of some xanthophylls in foods, although probably not to any significant degree.


The word phytochemicals means plant chemicals. Hundreds of phytochemicals are being studied. Many are believed to have a major positive impact on human health. Some contribute to the bright and vivid colors found in fruits and vegetables. The results of studies on specific phytochemicals are not necessarily applicable to the vegetables or fruits that harbor small concentrations of these chemicals.

Nevertheless, it is obvious that vegetables and fruits are healthful, which is probably due to some balance of phytochemicals, carotenoids, vitamins, fibers, and minerals rather than any single substance.

The benefits of individual phytochemical supplements are largely unproven. Furthermore, they are not regulated and high concentrations of some may behave like drugs and can be toxic and possibly even contribute to cancer cell growth.

Polyphenols and Flavonoids

Polyphenols are important phytochemicals, and flavonoids (or catechins) are members of the polyphenol family that may have significant health benefits. Laboratory studies have shown that specific flavonoids suppress tumor growth, interfere with sexual hormones, prevent blood clots, and have anti-inflammatory properties. In general, flavonoids are found in celery, cranberries, onions, kale, dark chocolate, broccoli, apples, cherries, berries, tea, red wine or purple grape juice, parsley, soybeans, tomatoes, eggplant, and thyme. Most common berries contain flavonoids and are particularly rich in potent antioxidants.

Among the important flavonoids are resveratrol, quercetin, and catechin. Evidence suggests that resveratrol (found in red wine, grapes, olive oil) may be extremely potent. In laboratory studies, it increases cell survival and has been shown to increase the life span of worms and fruit flies. Catechins are the primary flavonoids in tea and may be responsible for its possible beneficial effects. Flavonoids in dark chocolate may also be health protective.

Isoflavones (Phytoestrogens)

Isoflavones, commonly known as phytoestrogens, have actions that are similar to the female hormone estrogen. Isoflavones include compounds called genistein, daidzein, enterolactone, and equol. They act as antioxidants and tumor suppressors. These compounds may improve cholesterol, prevent bone loss, and suppress enzymes that stimulate certain cancers. Isoflavones are mainly found in soy products (not soy sauce) with smaller amounts found in chickpeas, flax and other seeds, barley, and milk products from cows feeding on clover.

Lignan is another phytoestrogen and is found in the fiber layers of whole-grains, berries, some seeds, some vegetables, and a few fruits.


Isothiocyanates and related substances, indoles, are also known as mustard oils and are responsible for the sharp taste in cruciferous (also called brassica) vegetables. Such vegetables include broccoli, cabbage, Brussels sprouts, cauliflower, collards, kale, kohlrabi, mustard greens, rutabaga, turnips, and bok choy. Isothiocyanates also stimulate enzymes that convert estrogen to a more benign form and may block steroid hormones that promote breast and prostate cancers. (Cruciferous vegetables are also high in fiber, vitamin C, and selenium.)


Monoterpenes have two important phytochemicals, perillyl alcohol and limonene. They block proteins that stimulate cell growth and reproduction and are being tested for actions against cancer. Limonene is found in the peels of citrus fruits.

Organosulfur Compounds

Organosulfurs are part of the allium family of phytochemicals. Compounds, such as allicin, may have benefits on the immune system, assist the liver in rendering carcinogens harmless, and reduce production of cholesterol in the liver. These compounds are found in garlic, leeks, onions, chives, scallions, and shallots.


Saponins are forms of carbohydrates that neutralize enzymes in the intestines that may cause cancer. They also may boost the immune system and promote wound healing. Saponins are found in ginseng, beans (including soy beans) and whole grains.


Capsaicin seems to reduce levels of substance P, a compound that contributes to inflammation and the delivery of pain impulses from the central nervous system. Research suggests that it may inhibit cancer-generating substances. It is found in hot red peppers.


Sterols, which include sitosterol, stigmasterol, campesterol, and squalene, are found in vegetable oils. Sitosterol is the most studied and appears to have cholesterol-lowering effects.

Beta-sitosterols may help improve urine flow and urinary symptoms in men with enlarged prostate glands (benign prostatic hyperplasia, or BPH). A recent review study of five randomized trials (519 men) found that urinary flow and other urinary symptoms improved in men who took the herbal remedy from 4 - 26 weeks. The study’s authors cautioned that while beta-sitosterols show effectiveness in the short term, their long-term effectiveness, ability to prevent complications from BPH, and safety are not known. More research is necessary. Beta-sitosterols come from South African star grass, Hypoxis rooperi, or species of Pinus and Picea.

Healthy Foods

Evidence increasingly suggests that a varied diet, not individual food chemicals, is essential for basic health and a longer life. Such diets are rich in fresh fruits and vegetables and whole grains, and low in saturated fats.

Some Examples of Healthy Foods


Phytochemicals and Carotenoids

Vitamins and other valuable food components





May have activity against certain cancers (lung). Also may help maintain healthy cholesterol. May protect against asthma.



Folate, iron, potassium, and zinc

Some experts believe beans are the perfect food.

Berries, all kinds of dark colored

Ellegic Acid

Vitamin C, minerals

The anthocyanins in berries such as bilberries, blueberries, cranberries, elderberries, and others, have numerous healthful properties including anti-cancer and antioxidant effects. Bilberry (Vaccinium myrtillis) is widely used to prevent macular degeneration. Blueberries may protect the aging brain. (In one study blueberries were most effective.)

Broccoli (also kale, Brussels sprouts, cauliflower)

Flavonoids, isothiocyanates, lutein, beta and alpha carotene. Note: Young sprouts of broccoli and cauliflower contain much higher levels of isothiocyanates than their mature forms.

Vitamin C, folate, fiber, and selenium

Anticancer properties. Protective against heart disease and stroke.

Carrots and other bright yellow vegetables

Lutein, beta carotene and other provitamin A carotenoids

Vitamin A (converted from carotenoids), vitamin C

Protects eyes, lungs. (Cooking carrots may increase the potency of food nutrients.)

Chocolate, dark. Note: Milk chocolate does not have benefits.



Heart protective (may improve lipids and help prevent blood clotting. May have protective properties against lung cancer (not other cancers).



Many B vitamins, vitamin A, vitamin D

Although egg yolks are high in cholesterol, very little of it has a negative effect on people with normal levels. And the health benefits of eggs are now known to be very high. (People with diabetes or those with high cholesterol should restrict eggs, however.)

Fish, oily (mackerel, salmon, sardines)


Vitamin B3, B12. Essential fatty acids, selenium

Heart and brain protective.


Allium (organosulfurs)


Possibly protective against certain cancers, heart diseases, and infection. Heating garlic can reduce benefits. Allowing crushed fresh garlic to stand 10 minutes before heating, however, may preserve beneficial chemicals while cooking.




Cancer fighting properties.

Grains (whole)

Lignans (phytoestrogens)

Vitamin B, Selenium (important antioxidant mineral), fiber, folate

May help reduce the ability of cancer cells to invade health tissue.

Grapes, including purple grape juice, and red wine

Flavonoids, (resveratrol, quercetin and catechin)


Fight heart disease and cancer. May help lower the risk for asthma.



Vitamin E, vitamin B1, essential fatty acids, folate

Protects the heart and may help prevent stroke.


Flavonoids, allium (organosulfurs)


May have activity against certain cancers (lung).



Vitamin C, folate, potassium.

Many health benefits. Increases HDL levels.

Potatoes (Sweet)


Vitamin C, vitamin E, vitamin A

Many health benefits.

Soy. The best products are tofu, soy milk, or whole soy protein.

Isoflavones (phytoestrogens), flavonoids, phytosterol, phytate, saponins.


May have effects similar to estrogen, including maintaining bone and benefiting the heart in women. May also be protective against prostate cancer and possibly other cancers. More studies are needed. Effects on breast cancer are uncertain. (Note: Soy may have different effects in men than in women. Of some concern is one study reporting more mental decline in men who consume greater amounts of tofu.)

Spinach and other dark green leafy vegetables

Zeaxanthin, Beta carotene

Vitamin C, folate, vitamin A (converted from carotenoids)

Protects lungs and brain.

Tea (Both black and green tea are beneficial. Best results associated with green tea.)

Flavonoids (primarily catechins)


Cancer fighting properties, particularly in green tea, which may be especially beneficial for smokers.

Both black and green tea may protect against heart disease and stroke, although studies are mixed.

Tea drinking also may help with weight control and help prevent osteoporosis.


Lycopene, Flavonoids

Vitamin C, biotin, minerals

Studies link to reductions in prostate and other cancers. Infection fighters.

Note on Organic versus Inorganic Products. There is some evidence that organic produce has higher levels of antioxidants and that some agricultural chemicals may destroy flavonoids. Nevertheless, organic produce is expensive, and fruits and vegetables, no matter how they are grown, are still filled with healthful nutrients.


Dietary Health Benefits

The benefits of any dietary factors are very difficult to prove, and, to date, there is no hard evidence that any supplement protects against any major disease. Studies on population groups may not consider other lifestyle or genetic factors. They often rely on people self-reporting their own dietary habits and often such surveys only reflect short-term eating habits. Other studies are done in the laboratory on animals or blood samples, which may not reflect the effects of nutrients on humans. Nevertheless, it is never wrong to eat plenty of fresh fruits and vegetables and whole grains, the primary sources of vitamins, carotenoids, and vitamins, as well as of fiber and important minerals.

Antioxidants: Pros and Cons

Description of Oxygen-Free Radicals (Oxidants)

Currently, the most important benefit claimed for vitamins A, C, E, and many of the carotenoids and phytochemicals is their role as antioxidants, which are scavengers of particles known as oxygen-free radicals (also sometimes called oxidants). These chemically active particles are by-products of many of the body's normal chemical processes. Their numbers are increased by environmental assaults, such as smoking, chemicals, toxins, and stress. In higher levels, oxidants can be very harmful in the following way:

  • They can damage cell membranes and interact with genetic material, possibly contributing to the development of a number of disorders including cancer, heart disease, cataracts, and even the aging process itself.
  • Oxygen-free radicals can also enhance the dangerous properties of low-density lipoprotein (LDL) cholesterol, a major player in the development of atherosclerosis.

Description of Antioxidants and Warnings on High-Dose Supplements

Antioxidant vitamins (A, C, and E), carotenoids, and many phytochemicals can neutralize free radicals. Unfortunately, although it is clear that vitamins are required to prevent deficiency diseases, high doses of vitamin C, vitamin E, and beta carotene supplements may also have pro-oxidant effects, which can be harmful in patients with cancer. In these people, high doses of antioxidant vitamins may actually protect cancer cells just as they do healthy cells.

The strongest evidence on negative effects to date comes from studies reporting an increase in lung cancer and overall mortality rates among smokers who took beta carotene supplements. In determining reasons for this disturbing effect, one animal study suggested that beta carotene increased enzymes in the lungs that actually promote cancerous changes. A 2000 study also reported a higher risk for cancer in male smokers who took multivitamins plus A, C, or E.

Some evidence also indicates that high doses of vitamin C may speed up atherosclerosis, or hardening of the arteries. In a 2003 study, women with heart disease who took antioxidant vitamins had a higher risk for heart attack or death than those who didn't take one.

A 2002 study also reported a higher incidence and greater severity of respiratory infections in older adults who took 200 mg of vitamin E daily. Some researchers speculate that certain immune factors generate oxidants to fight bacteria. This antioxidant vitamin, then, may block that action. Research published in 2005 suggests that those who take large amounts of vitamin E (1,500 IU/day) may slightly increase their risk for heart failure and death, but this evidence is not considered conclusive. Further study is necessary.

Protection Against Heart Disease

Vitamins and Heart Protection.

  • Antioxidant Vitamins A, C, and E. Deficiencies in vitamins A, C, E, and beta carotene have been linked to heart disease. All of these nutrients have antioxidant effects and other properties that should benefit the heart. However, several studies have found no reductions in heart disease in people who have taken antioxidant vitamins. In fact, a 2005 study has found that taking high doses of vitamin E is associated with an increased risk of heart failure. In 2003, the US Preventive Service Task Force concluded that, to date, evidence is insufficient to confirm or refute the benefits of supplements of any of these vitamins in protecting against heart disease. It is important to note, in addition, that each of these supplements may even be harmful to the heart in high doses.
  • Folate and B12 Vitamins. Deficiencies in the B vitamins folate (known also as folic acid) and B12 have been associated with elevated blood levels of homocysteine, an amino acid that has been associated with a higher risk for heart disease, stroke, and heart failure. Some studies in 2002, suggest that any risk posed by homocysteine or benefits from folic acid for heart disease are at most modest. One study, however, reported lower failure rates after heart surgery in patients who took folic acid and vitamins B12 and B6. And a major 2002 study suggested that lowering homocysteine levels with folic acid would reduce the risk for heart disease by 16% and stroke by 24%. More evidence is needed to determine whether homocysteine plays a causal role in cardiovascular disease and whether the B vitamins are protective. Folate improves blood flow through the arteries, which may be important for the heart, regardless of its effect on homocysteine.
  • Niacin. Niacin (vitamin B3) is used for lowering unhealthy cholesterol levels. Although vitamin B3 is available over the counter, it can have significant side effects. A physician should prescribe niacin in order to ensure its safety and effectiveness. [For more information, see In-Depth Report #23, Cholesterol.]

Carotenoids and Heart Protection. Studies have reported that a high intake of fruits and vegetables containing beta carotene, lycopene, and other carotenoids may reduce the risk of heart attack. For example, lycopene-poor diets (particularly lycopene in tomatoes) were associated with a significantly higher risk of heart disease and stroke. In another study involving animals, lutein protected against early hardening of the arteries.

Atherosclerosis is a disease of the arteries in which fatty material is deposited in the vessel wall, resulting in narrowing and eventual impairment of blood flow. Severely restricted blood flow in the arteries to the heart muscle leads to symptoms such as chest pain. Atherosclerosis shows no symptoms until a complication occurs.

Phytochemicals and Heart Protection. Several phytochemicals are associated with heart protection.

  • Flavonoids. Certain flavonoids, found in both black and green tea, dark chocolate, onions, red wine or red grape juice, and apples, appear to be strongly heart protective. In a 2003 study, people who consumed the most flavonoids in foods had a 20% lower risk for heart disease than those with low consumption. Flavonoids may protect against damage done by cholesterol and help prevent blood clots. A number of studies have now reported heart protection from the flavonoid catechin, which is found in both black and green tea. (Studies on tea-drinking however have been mixed. For example, the British consume a lot of tea but have high rates of heart disease.) The flavonoid resveratrol, which is found in grape skin, appears to be responsible for the well-known heart protective effects in red wine and purple grape juice. A glass or two of red wine a day may be healthful. For people who cannot drink alcohol, juice from red grapes may be beneficial.
  • Organosulfurs. Organosulfurs found in onions and garlic have been under investigation for possible beneficial effects on cholesterol levels. Two well-conducted studies found no heart-benefits from taking capsules equivalent to between one and one and a half garlic cloves a day. The preparation of these products, however, may be responsible for the lack of effect. On a more positive note, a 2000 study reported an association between taking garlic capsules and significantly lower cholesterol-build up in the arteries of older women but not in older men. In the study, daily garlic supplements dramatically reduced the build-up of newly formed plaque in the arteries, while having much less effect on older, harder plaque deposits. Garlic supplements for cardiovascular disease may be most beneficial, then, when used during earlier years among men and later years among women.
  • Isoflavones. Soy protein is the most studied source of isoflavones (known as phytoestrogens, or plant estrogens). Not all studies are consistent, but the majority has shown an improvement in at least one of the cholesterol components in people who consumed at least 25 grams of soy protein. Soy may also reduce other heart risk factors, at least in certain populations. For example, in one 2002 study, soy was beneficial for controlling blood sugar and lowering LDL in postmenopausal women with type 2 diabetes. In another study, soy protein was associated with lower systolic blood pressure in men. The best sources are soy products (tofu, soy milk) or whole soy protein. Powdered soy protein that contains at least 60 mg of isoflavones may provide similar benefits. Tablets of individual isoflavones found in soy do not appear to offer any advantages and may be harmful.
  • Sterols. The plant sterols, including sitosterol, are also proving to be potent cholesterol fighters. Sitostanol, a derivative of sitosterol, is being used in new margarine products to lower cholesterol levels.

Protection Against Stroke

A healthy diet rich in fruits and vegetables and low in salt and saturated fats may significantly lower the risk for a first stroke, perhaps by helping to protect against high blood pressure -- a major risk factor for stroke.

Vitamins and Stroke Protection. The effects of antioxidant vitamins and carotenoids on stroke, dementia, or both are being studied. Studies are conflicting, however. A very important 2001 study reported no protection stroke with vitamins A, E or beta carotene.

The B vitamin folate (usually in the form of folic acid) may protect against stroke. Studies have suggested that people who have higher blood levels of folate have a lower than average risk for stroke. Its primary benefit in this case appears to be to reduce levels of homocysteine, an amino acid that has been strongly linked to an increased risk of coronary artery disease, stroke, and Alzheimer's disease. A major 2002 study suggested that lowering homocysteine levels with folic acid would reduce the risk for heart disease by 16% and stroke by 24%.

Carotenoids and Stroke Protection. Some, but not all, studies have reported a lower risk of stroke from carotenoids, including beta carotene and lycopene.

Protection Against Cancer

Many fresh fruits and vegetables contain chemicals that may fight many cancers, including lung, breast, colon, and prostate cancers. Examples of important cancer fighting foods include the following:

  • Cruciferous vegetables (e.g., cabbage, Brussels sprouts, broccoli).
  • Tomatoes (which contain lycopene).
  • Carrots (which contain alpha carotene).

Some evidence suggests that antioxidants may enhance the anticancer effects of chemotherapy. In multiple studies, patients who maintained their antioxidant levels were better able to withstand the high stress caused by chemotherapy or radiation therapy compared to those with low antioxidant levels. Antioxidant nutrients that may help reduce the side effects of chemotherapy include vitamins E and C, beta carotene, genistein and daidzein (isoflavones found in soy), and quercetin (found in red wine an purple grape juice).

Any protective effects of vitamins or specific phytochemical against cancer, however, appear to depend on the cooperative effort among them. Individual supplements of any vitamin or food chemical have not as yet shown any benefits.

Vitamins and Cancer Protection. Because many cancers are thought to be initiated by the effects of oxygen-free radicals on DNA, the antioxidants A, C, and E and beta carotene have been intensively studied. A major study found that men who took selenium for 6 or 7 years reduced their risk of prostate cancer by 52%. Nevertheless, most individual supplements have not been proven to protect against cancer, and high doses may be dangerous.

  • Vitamin A, C, and E. Although some studies have reported an association between low blood levels of these antioxidant vitamins and a higher risk for cancer, supplements of vitamins A, C, and E appear to have no advantages in most cases. And there are some studies finding higher cancer risks with high intakes of antioxidants. For example, a 2003 study reported a higher risk in melanoma in people with vitamin-C rich diets. A 2000 study also reported a higher risk for cancer in male smokers who took multivitamins plus A, C, or E. (Vitamin E may be protective against bladder cancer.)
  • Vitamin D. Some studies have suggested that certain vitamin D compounds may inhibit certain cancer cells, specifically prostate cancer, from proliferating. More research is needed.
  • Folic acid and B12. These B vitamins convert the amino acid homocysteine to methionine, a substance that helps prevent cells from becoming malignant. Folic acid may provide some protection against cervical and colon cancer. One small study showed a reduction of lung cancer cells in smokers taking folic acid and vitamin B12, but the study was very small, of short duration, and other factors might have biased the results. Still another study reported that folic acid may reduce the risk for breast cancer among women who regularly drink alcohol. (In the study, folic acid had no other effect on breast cancer.)

In 2006, a study for the National Institutes of Health reviewed randomized trials evaluating the effectiveness and safety of multivitamin and mineral supplements in preventing cancer and chronic disease. The studies had mixed results, and some supplements reduced cancer rates in certain populations. However, the reviewers concluded that current evidence is not sufficient to determine whether multivitamin and mineral supplements may prevent cancer and chronic disease.

Carotenoids and Cancer Protection. A number of studies have reported that fruits and vegetables rich in carotenoids are associated with protection against many cancers. Lycopene, found in tomatoes, may have particular value in protection against prostate, colon, lung, and bladder cancer. A 2005 study found that in one out of four men with genetic variations that cause them to be more sensitive to oxidative stress, supplementation with selenium, vitamin E, and lycopene significantly reduces the risk of prostate cancer. Individual supplements, however, do not offer any advantage. In fact, evidence now strongly suggests that beta carotene supplements increase the risk for lung cancer in smokers.

Phytochemicals and Cancer Protection. The following phytochemicals appear to have cancer-protecting properties.

  • Isothiocyanates. Isothiocyanates and sulforaphane, found in cruciferous vegetables, may block the effects of carcinogens and suppress tumor growth. In one study, for example, women with the highest consumption of cruciferous vegetables had a 24% lower risk of breast cancer than women with the lowest consumption.
  • Isoflavones. Isoflavones, found in soy beans and flax seed, behave like estrogen in some ways and not in others. Researchers are very interested, then, in their effects on hormone-related cancers, including breast and prostate cancers. Much research has focused on soy. In general, a number of Asian studies have reported an association between a higher intake of soy and a lower incidence of reproductive and breast cancers. The effects of phytoestrogens, however, in all women are far from settled. Some evidence suggests the genistein in soy may have properties that are protective against lung cancer. Nonfermented soy products (tofu, soy milk) also may protect against stomach cancer, while fermented soy products (miso, soy paste) appears to increase the risk.
  • Flavonoids. Flavonoids and polyphenols, including those found in apples, dark chocolate, onions, tea, and red wine, are coming under strong scrutiny for possible cancer fighting properties. In one 24-year study, people who ate flavonoid-rich foods had a 20% lower risk for cancer in general. Resveratrol is a particularly potent polyphenol found in grapes and red wine. It has been found have tumor-suppressing properties. In studies on mice it has reduced tumor promotion and progression. Quercetin, another polyphenol, may also be protective.
  • Organosulfurs. The organosulfur compounds found in the onion and garlic family may have very potent properties in suppressing or blocking carcinogenic substances. Studies indicate that people who regularly consume fresh or cooked garlic have about half the risk of developing stomach cancer and two thirds the risk of colorectal cancer as people who eat little or no garlic. One possible explanation for garlic's anti-cancer effect in the stomach is its antibacterial action against H. pylori, which can promote stomach cancer. Taking garlic supplements, however, did not offer these benefits.

It should be noted that studies on the health benefits of vitamins and minerals have some important limitations. Some are held to rigorous standards, while others are not. In most cases, the results of existing research are complex, as they can easily be complicated by factors such as diet, exercise, the presence of healthy or unhealthy lifestyle behaviors, environmental factors, and more.

Evidence of Protection Against Other Diseases with Vitamins, Carotenoids, and Phytochemicals

Disease or Condition


Carotenoids, Phytochemicals, and Healthy Foods


Alzheimer's Disease

Vitamin E. Some reports, including a large 2002 population study, have suggested that vitamin E intake, from food or supplements, may protect against mental decline. (One study suggested that the vitamin protected only those who carried the apoE4 gene. No strong evidence to date has found any protection from antioxidant supplements.)

B Vitamins. Some studies suggest that deficiencies of the B vitamins B6, B12, and folate may be a risk factor for Alzheimer' diseases, possibly because deficiencies elevate homocysteine levels, which some research now associated with a higher risk for Alzheimer's disease. Of these, folates may offer the best protection.

According to several studies, eating plenty of darkly colored fruits and vegetables may slow brain aging. Of interest was a 1999 study on animals, in which extracts taken from blueberries and strawberries actually reversed age-related decline in brain function. Blueberries were the most effective.

The estrogen-like properties in isoflavones are of interest in the study of Alzheimer's disease. Animal studies suggest that soy might be protective against AD, particularly in postmenopausal women. Of some concern, however, were one population and a few animal studies suggesting that soy intake may pose a risk for greater mental decline among older men. More research is needed to confirm the effects of soy on the aging brain and to determine if there are gender differences.


Infectious Disease

Studies are mixed whether vitamin supplements protect against upper respiratory infections. Large doses of vitamin C, for example, may help reduce the duration of a cold, but they do not appear to protect against one in the first place, even after exposure to a cold virus. Two studies in 2002 on multivitamins reported opposite results, with one finding fewer infections and one finding no difference. It is possible that vitamin C or multivitamin supplements may be helpful in specific people, such those who are vitamin deficient or have medical problems that impair their immune systems.

Studies on vitamin E specifically have been mixed. A 2002 study, in fact, reported a higher incidence and greater severity of respiratory infections in older adults who took 200 mg of vitamin E daily. However, a 2004 clinical trial conducted among elderly nursing home residents found that daily supplementation with 200 IU of vitamin E did provide protection from upper respiratory infections, especially the common cold. At present, there is not enough evidence to recommend vitamin E for infection prevention.

Lycopene, found in tomatoes, appears to have properties that protect infection-fighting white blood cells.

Saponins extracted from ginseng and allicin (found in garlic) have properties that boost the immune system. Both ginseng and garlic have long been traditionally used for their health benefits.



Vitamin C from diet has been associated with lower risk for asthma. Supplements do not appear to provide benefit. In one study, some people with exercise-induced asthma benefited from taking vitamin C one hour before strenuous physical activity.

A study in 2001 suggested that flavonoids found in apples and red wine may help lower the risk for asthma. Some evidence indicates that a low dietary intake of antioxidant nutrients could increase the risk for lung damage. Such nutrients should be obtained from fresh, deep green and yellow-orange fruits and vegetables.


Eye Disorder

Cataracts and Macular Degeneration. Oxygen-free radicals play a role in cataract formation and age related macular degeneration, the most common cause of irreversible blindness in the elderly. Bilberry (Vaccinium myrtillis), which contains powerful anthocyanins, is widely used to prevent macular degeneration.

Low levels of vitamin C in the lens of the eye have been particularly strong predictors of cataracts. People with cataracts are frequently deficient in vitamin A, the carotenes, lutein, and zeaxanthin. Studies on protection against cataracts using antioxidant supplements have been mixed, including two identically conducted studies that reported opposite results. Vitamin C currently has the strongest evidence for protection, but even with this antioxidant studies are not consistent.

A combination of zinc and antioxidants, including vitamin C and E, may slow the progression of macular degeneration. (Vitamin E alone does not appear to be protective.)

Glaucoma. Although no evidence exists that antioxidants will prevent glaucoma, some studies reported an association between vitamin E and improved visual fields in patients with glaucoma.

Several studies report that the consumption of antioxidant-rich foods is associated with a decreased risk for cataracts. Carotenoids, especially lutein lycopene, and zeaxanthin are especially eye-protective and may help prevent cataracts and macular degeneration.


Skin Disorders and Wrinkles

One small study found that taking a combination of vitamins oral C and E supplements may help reduce sunburn reactions, although the protection is much less than from sunscreens. Taking the vitamins singly did not have any effect. In fact, a 2002 study reported that oral vitamin C had no effect on sunburn reaction. Of concern, in the same study some natural antioxidants in the body were reduced in people who took the vitamin.

Also of concern are studies reporting no benefits and possibly harm from topical vitamin C in the form of ascorbyl palmitate, which is soluble in fat.

A 2001 study reported that older adults had fewer wrinkles if they ate whole grains, fresh fruits and vegetables, and the use of healthy oils (such as olive oil). Diet played a role in improving skin regardless of whether the people in the study smoked or lived in sunny countries.

The following foods and phytochemicals may be especially skin protective:

Both green tea and ginger appear to have properties that may provide some protection against skin cancer. Green tea skin care products are now available.

The substance silymarin, found in the milk thistle family (which includes artichokes), may inhibit UVB-promoted cancers in animals.

In one interesting study, eating garlic protected animals very effectively against UVB damage by interfering with urocanic acid in the skin. Whether these results may apply to humans (and what quantities of garlic might be beneficial) is still unknown.



Vitamin D. Vitamin D is the essential companion to calcium in maintaining strong bones. Supplements may be needed for people who have poor exposure to sunlight. It should be noted that diet supplies most people's need and high amounts of vitamin D can be toxic. Of interest: Taking vitamin D supplements does not prevent bone loss in post-menopausal African American women, according to research published in 2005. Further study will be needed to determine whether vitamin D prevents bone loss in women from other ethnic groups.

Vitamin K. Studies suggest that vitamin K has properties that protect bone and prevent fracture. Vitamin K2 (menatetrenone), a form of vitamin K, is proving to prevent fractures in people with osteoporosis. Vitamin K affects blood clotting, and supplements are not recommended without specific physician instruction.

Vitamin B12. One study reported that in people with osteoporosis and pernicious anemia, taking vitamin B12 (which is used to treat the anemia) also increased bone density.

Vitamin C and E. There has been some indication of a positive association between vitamin C and E intake and bone density, although evidence proving actual benefits is weak.

Note on Vitamin A. High amounts of dietary vitamin A reduces bone density and may even increase the risk for fracture in both postmenopausal women and men. (A form of vitamin A, retinoic acid, has been found to stimulate bone break down.) Beta carotene does not appear to increase risk.

Studies suggest that diets rich in fresh fruits and vegetables (which include those high in potassium and magnesium) reduce elimination of calcium from the body and help preserve bones.

Studies are suggesting that isoflavones-rich soy products may actually improve bone density in postmenopausal women. However, some evidence suggests that separate supplements of isoflavones (e.g. genistein and daidzein) derived from soy do not provide the benefits of the whole protein like compounds. In fact, animal studies suggest that taking them separately may cause harm, including a possible increase in estrogen-related cancers. (Studies suggesting this have used animals or laboratory evidence. To date, there is no evidence of harm for humans who eat soy products.) More research is needed.

Flavonoids and other compounds in tea may protect the bones.


Menstrual Disorders

Vitamin B6. Limited clinical evidence suggests that vitamin B6 may be beneficial in reducing premenstrual symptoms, including depression. Typically, women take 100 mg per day, although one study suggested that a lower dose (50 mg) may have the same effect. Other preliminary research indicates that women who receive the equivalent of 1200 mg of calcium and 400 IU of vitamin D per day (through food or supplements) have a significantly lower incidence of premenstrual symptoms than women who did not.

Vitamin B1. One study reported relief from menstrual pain using vitamin B1 (thiamin).

Vitamin E. Several randomized controlled trials have shown that vitamin E significantly improves both physical and emotional premenstrual symptoms. One study reported that high doses of vitamin E helped reduce menstrual cramps. The doses were much higher than those recommended and could possibly increase the risk for bleeding.

Although anecdotal evidence reports that vitamin E helps reduce the frequency of hot flashes for menopausal women, there is no clinical evidence to support this claim.




Lots More Information



Wilt T, Ishani A, MacDonald R, Stark G, Mulrow C, Lau J. Beta-sitosterols for Benign Prostatic Hyperplasia (Cochrane Review). Chichester, UD: John Wiley & Sons, Ltd.; Issue 3, 2006.

Huang HY, Caballero B, Chang S, et al.The efficacy and safety of multivitamin and mineral supplement use to prevent cancer and chronic disease in adults: A systematic review for a National Institutes of Health State-of-the-Science Conference. Ann Intern Med. 2006 Jul 31; [Epub ahead of print]

Bairati I, Meyer F, Gelinas M, et al. Randomized trial of antioxidant vitamins to prevent acute adverse effects of radiation therapy in head and neck cancer patients. J Clin Oncol. 2005 Aug 20;23(24):5455-7.

Borek C. Dietary Antioxidants and Human Cancer. Integrative Cancer Therapies. 2004 3: 333-341.

Prasad KN. Multiple Dietary Antioxidants Enhance the Efficacy of Standard and Experimental Cancer Therapies and Decrease Their Toxicity. Integrative Cancer Therapies. 2004 3: 310-322.

Li, H, Kantoff PW, Giovannucci P et al. Manganese Superoxide Dismutase Polymorphism, Prediagnostic Antioxidant Status, and Risk of Clinical Significant Prostate Cancer. Cancer Research. 2005;65: 2498-2504.

Villa P. L-folic acid supplementation in healthy postmenopausal women: effect on homocysteine and glycolipid metabolism. J Clin Endocrinol Metab. 2005; 90(8): 4622-9.

Duffield-Lillico AJ, Reid ME, Turnull BW, et al. Baseline characteristics and the effect of selenium supplementation on cancer incidence in a randomized clinical trial: A summary report of the Nutritional Prevention of Cancer Trial. Cancer Epid Biomarkers. Prev 11:630-639, 2002.

Heinonen OP, Albanes D, Huttunen JK, et al. Prostate cancer and supplementation with alpha-tocopherol and beta-carotene: incidence and mortality in a controlled trial. J. Natl Cancer Inst. 90:440-6, 1998.

Corrada MM, Kawas CH, Hallfrisch J, Muller D, Brookmeyer R.Reduced risk of Alzheimer’s disease with high folate intake: The Baltimore Longitudinal Study of Aging. Alzheimer's & Dementia: The Journal of the Alzheimer's Association. 2005;1:11-18.

Miller ER 3rd, Pastor-Barriuso R, Dalal D, Riemersma RA, Appel LA, Guallar E. Meta-analysis: High-dosage vitamin E supplementation may increase all-cause mortality. Ann Intern Med. 2005;142:37-46.

Levy AP, Gerstein HC, Miller-Lotan R, Ratner R, McQueen M, Lonn E, Pogue J. The Effect of Vitamin E Supplementation on Cardiovascular Risk in Diabetic Individuals With Different Haptoglobin Phenotypes. Diabetes Care. 2004 27: 2767.

Lonn E, Bosch J, Yusef S, et al. Effects of long-term vitamin E supplementation on cardiovascular events and cancer: a randomized controlled trial.JAMA. 2005;293:1338-1347.

Etminan M, Gill SS, Samii A. Intake of vitamin E, vitamin C, and carotenoids and the risk of Parkinson's disease: a meta-analysis Lancet Neurol.2005; 4(6): 362-5.

The HOPE and HOPE-TOO Trial Investigators. Effects of Long-term vitamin E supplementation on cardiovascular events and cancer: A randomized controlled trial. JAMA. 293:1138-1347, 2005.

Clark L.C., Combs GF Jr, Turnbull B.W., et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. A randomized controlled trial. Nutritional Prevention of Cancer Study Group. JAMA. 276:1957-1963, 1996.

Duffield-Lillico AJ, Reid ME, Turnull BW, et al. Baseline characteristics and the effect of selenium supplementation on cancer incidence in a randomized clinical trial: A summary report of the Nutritional Prevention of Cancer Trial. Cancer Epid Biomarkers. Prev 11:630-639, 2002.

Heinonen OP, Albanes D, Huttunen JK, et al. Prostate cancer and supplementation with alpha-tocopherol and beta-carotene: incidence and mortality in a controlled trial. J. Natl Cancer Inst. 90:440-6, 1998.

Weinstein SJ, Wright ME, Pietinen P, et al. Serum alpha-tocopherol and gamma-tocopherol in relation to prostate cancer risk in a prospective study. J Natl Cancer Inst. 97:396-399, 2005.

The Heart Outcomes Prevention Evaluation Study Investigators. Effects of an angiotensin-converting-enzyme inhibitor, ramipril, on cardiovascular events in high-risk patients. N Engl J Med. 342: 145-153, 2000.

The Heart Outcomes Prevention Evaluation Study Investigators. Vitamin E supplementation and cardiovascular events in high-risk patients. N Engl J Med. 342: 154-160, 2000.

John F. Aloia, MD; Sonia Arunabh Talwar, MD; Simcha Pollack, PhD; James Yeh, PhD. A Randomized Controlled Trial of Vitamin D3 Supplementation in African American Women. Arch Intern Med. 2005; 165: 1618 – 1623.

Bertone-Johnson ER Hankinson SE, Bendich A, Johnson SR, Willett WC, Manson JE. and vitamin D intake and risk of incident premenstrual syndrome. Arch Intern Med. 2005; 165:1246-1252.

Miller ER 3rd, Pastor-Barriuso R, Dalal D, Riemersma RA, Appel LA, Guallar E. Meta-analysis: High-dosage vitamin E supplementation may increase all-cause mortality. Ann Intern Med. 2005;142:37-46.

Yusuf S, Dagenais G, Pogue J, Bosch J, Sleight P. Vitamin E supplementation and cardiovascular events in high-risk patients. The Heart Outcomes Prevention Evaluation Study Investigators. N Engl J Med. 2000;342:154-60.

McNeil JJ, Robman L, Tikellis G, Sinclair MI, McCarty CA, Taylor HR. Vitamin E supplementation and cataract: randomized controlled trial. Ophthalmology. 2004;111:75-84.

Lonn E, Bosch J, Yusef S, et al. Effects of long-term vitamin E supplementation on cardiovascular events and cancer: a randomized controlled trial.JAMA. 2005;293:1338-1347.

Bagchi D, Sen CK, Bagchi M, Atalay M. Anti-angiogenic, antioxidant, and anti-carcinogenic properties of a novel anthocyanin-rich berry extract formula.Biochemistry (Mosc). 2004;69(1):75-80, 1 p preceding 75.

Roy S, Khanna S, Alessio HM, Vider J, Bagchi D, Bagchi M, Sen CK. Anti-angiogenic property of edible berries.Free Radic Res. 2002 Sep;36(9):1023-31.

Blodi BA, Nutritional supplements in the prevention of age-related macular degeneration. Insight. 2004 Jan-Mar;29(1):15-6; quiz 17-8.

Head KA, Natural therapies for ocular disorders, part two: cataracts and glaucoma. Altern Med Rev. 2001 Apr;6(2):141-66.

Reference – this article was sourced from howstuffworks