Vitamin A is a fat-soluble vitamin that has several important functions in the body:

• It helps cells reproduce normally (called “cellular differentiation”).
• It is essential for good vision -- the first sign of a vitamin A deficiency is often poor sight at night.
• It is necessary for the proper development of an embryo and fetus.

Vitamin A also helps keep skin and mucous membranes that line the nose, sinuses, and mouth healthy. It plays a role in proper immune system function, growth, bone formation, reproduction, and wound healing.

Vitamin A comes from two sources: a groups of molecules called retinoids (which are derived from animal sources and includes retinol) and another group called carotenoids (which are derived from plants and includes beta-carotene). The body converts beta-carotene to vitamin A.

Severe vitamin A deficiencies are rare in the developed world: symptoms can include dry eyes, night blindness, diarrhea, and skin problems.

While vitamin A is essential for good health, it can be toxic in high doses. Never exceed the recommended daily allowance without first talking to your doctor.

Acne, Psoriasis, and other Skin disorders

Topical and oral preparations containing retinoids (a synthetic form of vitamin A) can help clear up severe acne and psoriasis and have shown promise for treating other skin disorders, such as rosacea, premature aging from the sun, and warts. These medications are given by prescription and require careful monitoring by a physician. Isotretinoin (Accutane) can cause very serious side effects and must not be used by pregnant women or women of child-bearing age who are not taking some birth control.

Eye Disorders

Vitamin A supplements can improve symptoms of xerophthalmia (dry eye) and may be helpful in treating retinitis pigmentosa, a hereditary disease that causes poor night vision. In addition, a large population study found that people who got high levels of vitamin A though their diets (not through supplements) had a decreased risk of developing cataracts. However, it's not yet known whether taking more vitamin A would have the same effect.

Measles

Children who are deficient in vitamin A are more likely to develop infections (including measles). Vitamin A supplements reduce the severity and complications of measles in children. In areas of the world where vitamin A deficiency is widespread or where at least 1% of those with measles die, the World Health Organization recommends giving vitamin A supplements to children with the infection. However, vitamin A does not appear to help if a child is not deficient. Never give a child vitamin A supplements without a doctor's supervision.

Osteoporosis

If you are at risk for osteoporosis, it is important to get enough vitamin A -- but not too much. Vitamin A is necessary for normal bone development, and low levels of vitamin A may contribute to bone loss. However, higher doses (above 1,500 mcg, or 5,000 IU, per day) may lead to bone loss. Beta-carotene, which the body converts to vitamin A, doesn't appear to pose the same risk, so the best strategy is to get enough beta-carotene in your diet.

Inflammatory Bowel Disease (IBD)

Many people with IBD (both ulcerative colitis and Crohn's disease) have vitamin and mineral deficiencies, including vitamin A, because they cannot absorb enough from their diet. Health care providers often recommend that people with IBD take a multivitamin.

Cancer

Whether vitamin A can reduce the risk of cancer is a complicated question. Eating a healthy diet with enough beta-carotene and other carotenoids from fruits and vegetables may be associated with lower risk of certain cancers (such as breast, colon, esophageal, and cervical). And some laboratory studies suggest that vitamin A and carotenoids may help fight against certain types of cancer in test tubes.

But there is no proof that taking vitamin A supplements will help prevent or treat cancer. There is some evidence that it can do harm. Taking beta-carotene or vitamin A supplements has been linked to an increased risk of lung cancer in people who smoke or drink alcohol (although some researchers say more studies are needed to confirm this finding).

Some preliminary evidence suggests that a topical form of vitamin A, applied to the cervix (the opening to the uterus) may reduce mild-to-moderate cervical neoplasia (abnormal growth of cells on the cervix).

The use of retinoids (a synthetic form of vitamin A) for skin cancer is also being examined. Vitamin A and beta-carotene levels in the blood tend to be lower in people with certain types of skin cancer. However, results of studies examining whether taking higher amounts of vitamin A or beta-carotene would prevent or treat skin cancer have been mixed.

Alzheimer's Disease

Preliminary studies suggest that levels of vitamin A and beta-carotene may be significantly lower in people with Alzheimer's compared to healthy individuals. However, there is no evidence that taking a vitamin A supplement provides any benefit.

Vitamin A, in the form of retinyl palmitate, is found in beef, calf, and chicken liver; eggs; fish liver oils; and dairy products, including whole milk, whole milk yogurt, whole milk cottage cheese, butter, and cheese.

The body can also produce vitamin A from beta-carotene and other carotenoids (fat-soluble nutrients found in fruits and vegetables). Most dark-green leafy vegetables and deep yellow/orange vegetables and fruits (sweet potatoes, carrots, pumpkin and other winter squashes, cantaloupe, apricots, peaches, and mangoes) contain substantial amounts of beta-carotene. By eating these beta-carotene rich foods, you can increase levels of vitamin A in your body.

Vitamin A supplements are available as either retinol or retinyl palmitate. The body absorbs all forms of vitamin A.

Tablets or capsules are available in a variety of doses. The tolerable upper limit (or safe upper limit) is 10,000 IU. For any dose higher than that, a doctor should help you determine the amount to take. Most multivitamins contain the recommended dietary allowance (RDA) for vitamin A (see How To Take It).

In many cases, taking beta-carotene may be a safer alternative. Unlike vitamin A, beta-carotene does not build up in the body, so it can be taken in larger amounts without the same risk. However, there is some evidence that high doses of beta-carotene can carry some risk. Talk to your doctor before taking more than the recommended amount.

Vitamin A is absorbed along with fat in the diet. Take it during or shortly after a meal.

Therapeutic doses have ranged as high as 50,000 IU for adults. However, a health care provider should monitor any high-dose therapy (more than 10,000 IU for an adult or above the recommended daily allowance for a child).

Daily dietary intakes for vitamin A are:

Pediatric

• Infants birth to 6 months: 400 mcg or 1,333 IU of retinol (AI)
• Infants 7 - 12 months: 500 mcg or 1,667 IU of retinol (AI)
• Children 1 - 3 years: 300 mcg or 1,000 IU of retinol (RDA)
• Children 4 - 8 years: 400 mcg or 1,333 IU of retinol (RDA)
• Children 9 - 13 years: 600 mcg or 2,000 IU of retinol (RDA)
• Males 14 - 18 years: 900 mcg or 3,000 IU of retinol (RDA)
• Females 14 - 18 years: 700 mcg or 2,333 IU of retinol (RDA)

Adult

• Males 19 years and older: 900 mcg or 3,000 IU of retinol (RDA)
• Females 19 years and older: 700 mcg or 2,333 IU of retinol (RDA)
• Pregnant females 14 - 18 years: 750 mcg or 2,500 IU of retinol (RDA)
• Pregnant females 19 years and older: 770 mcg or 2,567 IU of retinol (RDA)
• Breastfeeding females 14 - 18 years: 1,200 mcg or 4,000 IU of retinol (RDA)
• Breastfeeding females 19 years and older: 1,300 mcg or 4,333 IU of retinol (RDA)

Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider.

Too much vitamin A taken during pregnancy can cause serious birth defects. Because all prenatal vitamins contain some vitamin A, taking any more during pregnancy can be dangerous.

Synthetic vitamin A can cause birth defects. For this reason, this type of vitamin A should not be used by pregnant women or women who are trying to become pregnant.

Too much vitamin A is toxic and can cause liver failure, even death. Symptoms of vitamin A toxicity include lasting headache, fatigue, muscle and joint pain, dry skin and lips, dry or irritated eyes, nausea or diarrhea, and hair loss. While vitamin A is considered safe in the diet, it is possible to get too much from supplements. For those 19 and older, the tolerable upper limit for vitamin A is 10,000 IU per day. Talk to your doctor before taking any more than that.

People who have liver disease should not take vitamin A supplements without their doctor’s supervision.

Smokers and those who consume heavy amounts of alcohol should not take beta-carotene supplements.

Both vitamin A and beta-carotene may increase triglycerides (fatty deposits in the body that rise after eating) and even increase risk of death from heart disease, particularly in smokers.

Vitamin A is found in many different types of vitamin formulas. Supplements that say "wellness formula," "immune system formula," "cold formula," "eye health formula," "healthy skin formula," or "acne formula," all tend to contain vitamin A. If you take a variety of different formulas, you could be at risk for too much vitamin A.

If you are being treated with any of the following medications, you should not use vitamin A without first talking to your health care provider.

Tetracycline antibiotics -- People who take a type of antibiotics called tetracyclines and also take high doses of vitamin A may be at risk for a condition called intracranial hypertension, a rise in the pressure of brain fluid. Tetracyclines include:

• Demeclocycline (Declomycin)
• Minocycline (Minocin)
• Tetracycline (Achromycin)

Antacids -- One study suggests that the combination of vitamin A and antacids may be more effective than antacids alone in healing ulcers.

Anticoagulants (blood thinners) -- Long-term use of vitamin A or taking high doses may increase the risk of bleeding for those taking blood-thinning medications, particularly warfarin (Coumadin). Talk to your doctor before taking vitamin A.

Cholesterol-lowering medications (bile acid sequestrants) -- The medications cholestyramine (Questram) and colestipol (Colestid) may reduce the body's ability to absorb vitamin A and lead to lower levels in the body. A water-soluble form of vitamin A may help. Another class of cholesterol-lowering medications called statins may actually increase vitamin A levels in the blood.

Doxorubicin -- Test tube studies suggest that vitamin A may enhance the action of doxorubicin, a medication used to treat cancer. More research is needed, however, to know whether this has any practical application. If you are undergoing treatment for cancer, talk to your oncologist before taking vitamin A or any supplement.

Neomycin (Mycifradin) -- This antibiotic may reduce the body's ability to absorb vitamin A, especially when taken in large doses.

Omeprazole -- Omeprazole (used for gastroesophageal reflux disease or "heartburn") may influence the absorption and effectiveness of beta-carotene supplements. It is not known whether this medication affects the absorption of beta-carotene from foods.

Retinoids -- These medications are a synthetic form of vitamin A and are sometimes prescribed in high doses. People who take retinoids should not take any additional vitamin A supplements. In addition, these drugs can cause severe birth defects. Women of child-bearing age must have two negative pregnancy tests and be on two forms of birth control before taking these medications. Anyone taking retinoids will be monitored closely by their doctor. Retinoids include:

• Acitretin (Soriatane)
• Bexarotene (Targretin)
• Isotretinoin (Accutane)
• Tazarotene (Avage)

Tretinoin (Retin-A) is usually prescribed for topical use to treat acne or reduce wrinkles and is not as concentrated as other retinoids. However, it is still a good precaution to avoid taking a vitamin A supplement while using Retin-A.

Orlistat (Alli) and Olestra -- Orlistat, a medication used for weight loss, and olestra, a substance added to certain foods, both prevent the body from absorbing fat and calories. They may also prevent the body from absorbing enough vitamin A. The Food and Drug Administration requires that vitamin A and other fat-soluble vitamins (namely, D, E, and K) be added to food products containing olestra. In addition, people who take either prescription orlistat or over-the-counter Alli may want to take a multivitamin.

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