Basics & Facts
Vitamin A is an umbrella term for several fat-soluble compounds such as retinol, retinyl esters, retinal and retinoic acid. Vitamin A comes in two main forms in foods. Preformed vitamin A (retinyl acetate, retinyl palmitate) can be found in dairy products, meat, poultry and seafood. Provitamin A, the most common type of which is beta-carotene, is found in plant-based foods and most vitamin supplements.
In any form, vitamin A works as an antioxidant in the body. Antioxidants can protect cells from the harms caused by free radicals (toxins produced by the environment or by-products of metabolism). Adequate vitamin A is needed for the proper functioning of many body organs and systems.
Sources of Vitamin A
According to the USDA National Nutrient Database, the three foods containing the most vitamin A are turkey giblets, carrot juice and canned pumpkin. It can also be found in significant quantities in the following:
- Organ meats, especially beef liver
- Green, orange and yellow vegetables including leafy greens
- Orange and yellow fruits such as cantaloupe, mangos, and apricots
- Fortified dairy products and cereals
Most combination dietary vitamin and mineral supplements contain some form of vitamin A. Vitamin A is also available by itself.
Vitamin A is used throughout the body. It contributes to normal vision in a number of ways, including the functioning of the retina and cornea. It supports proper growth of cells especially in the heart, lungs, bones and kidneys. Vitamin A also affects the immune system and reproductive system function. Research studies have revealed other roles vitamin A plays in several diseases and conditions:
- Preventing cancer: A high intake of vitamin A-containing foods is associated with a lower risk of lung cancer and prostate cancer. Vitamin A supplements, however, have not been shown to have the same benefit. Some studies suggest that people who smoke and take high doses of beta-carotene in supplement form may in fact have an increased lung cancer risk.
- Slowing the progression of age-related macular degeneration: This disease is a leading cause of vision loss among older Americans. Some people with the condition who take a supplement containing beta-carotene, zinc, copper and other antioxidants have a slower rate of vision loss.
- Lessening the severity of measles: Children with a preexisting deficiency of vitamin A tend to have more severe cases of the measles. In these cases, however, if the children are given high-dose vitamin A supplements, they may experience fewer fevers and less diarrhea. In developing countries, the supplements can lower the risk of death in children who come down with the disease.
Some topical derivatives of vitamin A are FDA-approved for treating conditions such as acne, psoriasis and aging skin.
Vitamin A deficiency is rarely seen in the U.S because most people get sufficient amounts from foods—many of which are fortified with various forms of the vitamin. Some groups of people, however, may need additional vitamin A. These include premature babies, vegetarians, alcoholics and young children. In addition, certain diseases such as cystic fibrosis, liver disease and Crohn’s disease affect how well the body can use vitamin A.
In developing countries, pregnant women and young children are especially vulnerable to vitamin A deficiency and many experience an eye condition called xerophthalmia, which can result in blindness. The most common symptom of this disease is dry eyes and an inability to see well in low light.
Most fat-soluble vitamins can be harmful in large doses because the body can’t eliminate them rapidly. In the case of vitamin A, it depends on which form people take.
- Too much preformed vitamin A, which typically occurs through over ingestion of supplements, can lead to dizziness, headaches, nausea or even coma and death. It can also cause congenital anomalies if pregnant women take too much.
- Too much provitamin A (such as beta-carotene) may cause a harmless yellowish-orange discoloration of the skin. Birth defects are not associated with high doses of beta-carotene. The FDA and USDA, however, have not established safe upper limits for provitamin forms of vitamin A.
The U.S. Food and Drug Administration has set a daily value (DV) of 5,000 IU of vitamin A from foods—both plant and animal. The DV, which is independent of age or sex, is found on supplement labels, and shouldn’t be confused with a recommended dietary allowance (RDA), which is the amount of a vitamin you need to take to avoid deficiencies.
The RDA for vitamin A can be confusing because it is measured in retinol activity equivalents (RAE), which are rarely seen on supplement labels. For men, 900 RAEs are recommended, and for women, about 700. This is roughly equivalent to 3,000 IU and 2,310 IU respectively.
Per the National Institutes of Health Office of Dietary Supplements, the safe upper limits for preformed vitamin A in various age groups are as follows:
- Birth to one year: 2,000 IU
- Children 1 to 3 years: 2,000 IU
- Children 4 to 8 years: 3,000 IU
- Children 9 to 13 years: 5667 IU
- Teens 14 to 18 years: 9,333 IU
- Adults 19 years and over: 10,000 IU
Vitamin A, while essential for many bodily functions, is not something that most American adults need to be particularly vigilant about because of its presence in so many foods. Nevertheless, everyone—especially in the case of pregnant women and children—should consult a healthcare provider for advice about how much vitamin A is necessary for them.
- MedlinePlus National Library of Medicine
- National Institute of Health
- National Institutes of Health Office of Dietary Supplements
- USDA National Nutrient Database
- PubMed: Xerophthalmia and Vitamin A Status
- Institute of Medicine
- Ohio State University Extension Fact Sheet
- American Academy of Pediatrics
- Mayo Foundation for Education and Research