Vitamin A

Vitamin A
By Mayo Clinic Staff
Overview
Vitamin A (retinol, retinoic acid) is a nutrient important to vision, growth, cell division, reproduction and immunity. Vitamin A also has antioxidant properties. Antioxidants are substances that might protect your cells against the effects of free radicals — molecules produced when your body breaks down food or is exposed to tobacco smoke and radiation. Free radicals might play a role in heart disease, cancer and other diseases.
Vitamin A is found in many foods, such as spinach, dairy products and liver. Other sources are foods rich in beta-carotene, such as green leafy vegetables, carrots and cantaloupe. Your body converts beta-carotene into vitamin A.

As an oral supplement, vitamin A mainly benefits people who have a poor or limited diet or who have a condition that increases the need for vitamin A, such as pancreatic disease, eye disease or measles. If you take vitamin A for its antioxidant properties, keep in mind that the supplement might not offer the same benefits as naturally occurring antioxidants in food.

The recommended daily amount of vitamin A is 900 micrograms (mcg) for adult men and 700 mcg for adult women.

Evidence
Research on oral vitamin A for specific conditions shows:

Acne. Large doses of oral vitamin A supplements don't appear to affect acne.
Age-related macular degeneration. A large clinical trial showed that people at high risk of advanced age-related macular degeneration reduced their risk of developing the condition by 25 percent by taking a specific combination of vitamins that included beta-carotene. It's not entirely clear what role beta-carotene played.
Cancer. The association between use of vitamin A supplements and reduced risk of lung, prostate and other types of cancer is unclear.
Measles. Vitamin A supplements are recommended for children with measles who are at an increased risk of vitamin A deficiency. Research suggests that supplementation might reduce death due to measles.
Vitamin A deficiency. People who have low levels of vitamin A appear to benefit most from vitamin A supplements. This kind of deficiency isn't common in the United States. Vitamin A deficiency causes anemia and dry eyes.
Beyond use as an oral supplement, vitamin A is used in topical creams to reduce fine wrinkles, splotches and roughness and treat acne.

Our take
Caution
A healthy and varied diet will provide most people with enough vitamin A. If you're interested in the antioxidant properties of vitamin A, food sources are best. It's not clear if vitamin A supplements offer the same benefits as naturally occurring antioxidants in food. Too much vitamin A can be harmful and excess vitamin A during pregnancy has been linked to birth defects.
Safety and side effects
Too much vitamin A can be harmful. Even a single large dose — over 200,000 mcg — can cause:

Nausea
Vomiting
Vertigo
Blurry vision
Taking more than 10,000 mcg a day of oral vitamin A supplements long term can cause:

Bone thinning
Liver damage
Headache
Diarrhea
Nausea
Skin irritation
Pain in the joints and bone
Birth defects
If you are or might become pregnant, talk to your doctor before taking vitamin A. Excess use of vitamin A during pregnancy has been linked to birth defects.

Interactions
Possible interactions include:

Anticoagulants. Oral use of vitamin A supplements while taking these medications used to prevent blood clots might increase your risk of bleeding.
Bexarotene (Targretin). Taking vitamin A supplements while using this topical cancer drug increases the risk of the drug's side effects, such as itchy, dry skin.
Hepatotoxic drugs. Taking high doses of vitamin A supplements can cause liver damage. Combining high doses of vitamin A supplements with other drugs that can damage the liver could increase the risk of liver disease.
Orlistat (Alli, Xenical). This weight-loss drug can decrease the absorption of food sources of vitamin A. Your doctor might suggest that you take a multivitamin with vitamin A and beta-carotene while taking this medication.
Retinoids. Don't use vitamin A supplements and these oral prescription drugs at the same time. This could increase the risk of high vitamin A blood levels.
@mayoclinic.org