Vitamin A Overview
Vitamin A is a fat-soluble antioxidant that protects your cells against damaging free radicals and plays other vital roles in the body. However, it is potentially more dangerous than most other vitamins because it can build up to toxic levels. For this reason, it should be used with caution.
It has long been assumed that beta-carotene supplements taken at nutritional doses are a safer way to get the vitamin A you need. However, while this may be true in general, beta-carotene also appears to present some risks. See the full Beta-Carotene article for more information.
Vitamin A is an essential nutrient—meaning you must get it in the diet. The official U.S. recommendations for daily intake of vitamin A ^ are expressed in international units (IUs) or retinol activity equivalents (RAE), which are measured in micrograms, as follows:
- 0-6 months: 400 mcg RAE or 1,330 IU
- 7-12 months: 500 mcg RAE or 1,665 IU
- 1-3 years: 300 mcg RAE or 1,000 IU
- 4-8 years: 400 mcg RAE or 1,330 IU
- 9-13 years: 600 mcg RAE or 2,000 IU
- 14 years and older: 900 mcg RAE or 3,000 IU
- 9-13 years: 600 mcg RAE or 2,000 IU
- 14 years and older: 700 mcg RAE or 2,330 IU
- Pregnant Women
- 18 years or younger: 750 mcg RAE or 2,500 IUs
- 19 years and older: 770 mcg RAE or 2,560 IU
- Nursing Women
- 18 years or younger: 1,200 mcg RAE or 4,000 IUs
- 19 years and older: 1,300 mcg RAE or 4,300 IU
Warning: Pregnant women should not take vitamin A supplements. Instead they should take beta-carotene.
We get vitamin A from many foods, in the form of either vitamin A or beta-carotene. Liver and dairy products are excellent sources of vitamin A. Carrots, apricots, collard greens, kale, sweet potatoes, parsley, and spinach are good sources as well.
Deficiency in vitamin A is common in developing countries. ^ In the developed world, deficiency is relatively rare. However, certain diseases can cause vitamin A deficiency by impairing the ability of the digestive tract to absorb nutrients. These include Crohn’s disease , ulcerative colitis , and cystic fibrosis.
Although some studies have used high doses of vitamin A, intake above the safe upper limit level is not recommended except on physician advice (see Safety Issues ).
What Is the Scientific Evidence for Vitamin A?
According to many ^ but not all ^ studies, people with diabetes tend to be deficient in vitamin A.
An observational study suggests that vitamin A supplements may improve blood sugar control in people with diabetes. ^ However, due to safety concerns, they should not supplement with vitamin A except under medical supervision (see Safety Issues ).
Menorrhagia (Heavy Menstruation)
One study suggests that women with heavy menstrual bleeding can benefit from taking 25,000 IU daily of vitamin A. ^ But vitamin A cannot be recommended as an ongoing treatment for menorrhagia, since women who menstruate can become pregnant, and even fairly low doses of supplemental vitamin A may cause birth defects.
One small double-blind study suggested that taking beta-carotene might raise white blood cell count in people with HIV . ^ However, two subsequent larger controlled trials found no significant differences between those taking beta-carotene or placebo in white blood cell count, CD4+ count, or other measures of immune function. ^ Two observational studies lasting 6 to 8 years suggest that higher intakes of vitamin A or beta-carotene may be helpful, but they also found that caution is in order with regard to dosage. ^ This group of researchers generally linked higher intake of vitamin A or beta-carotene to lower risk of AIDS and lower death rates, with an important exception: people with the highest intake of either nutrient (more than 11,179 IU per day of beta-carotene, more than 20,268 IU per day of vitamin A) did worse than those who took somewhat less.
Despite hopes that vitamin A given to pregnant, HIV-positive women might decrease the infection rate of their babies, two double-blind studies have found no significant differences between babies whose mothers took vitamin A compared to those whose mothers took placebo. ^ In any case, vitamin A is not considered safe in pregnancy; beta-carotene is preferred.
According to a double-blind study of 86 people with Crohn's disease , vitamin A does nothelp prevent flare-ups. ^