What Is Vitamin A?
Vitamin A is a fat-soluble nutrient that controls the growth of almost every cell in your body. You can get vitamin A naturally from certain foods. But, synthetic vitamin A can be consumed via fortified foods and supplements.
There are two main types of vitamin A.
- Preformed vitamin A. Preformed vitamin A like retinol comes from animal products including liver, egg, fish, and dairy.
- Provitamin A. Provitamin A like beta-carotene comes from plant sources and is converted into usable forms of vitamin A like retinol in your body. Provitamin A is found in carrots, tomatoes, cantaloupe, sweet potatoes, and leafy greens.
How Much Vitamin A Do You Need?
The recommended daily allowance of vitamin A — which is the amount of vitamin A you need to consume every day — is measured in retinol activity equivalents — or RAE — per day. Using RAE tells you how much vitamin A your body converts into retinol.
The recommended daily dose of vitamin A is 900 micrograms of RAE for men and 700 micrograms of RAE for women. Most people can easily get this in their regular diet without synthetic vitamin A supplements.
Sources of Vitamin A
Not all sources of vitamin A are equally useful to your body. When you consume vitamin A, its source (natural foods or synthetic supplements) and type (preformed vitamin A or provitamin A) matter.
Food. Good dietary sources of vitamin A or beta-carotene include:
- Leafy greens
- Orange and yellow vegetables
Getting your vitamin A through food rather than supplements is ideal. The health benefits of vitamin A from food sources are well established, but the benefits from synthetic supplements are not as clear.
Supplements. You might need a vitamin A supplement if you can’t get vitamin A through your diet or if you have certain medical conditions. Conditions that increase your need for vitamin A include pancreatic disease, certain eye diseases, and measles.
If you take a multivitamin, you probably already take enough vitamin A and don't need additional supplementation. Multivitamins typically contain 750 to 3,000 micrograms of RAE.
Your vitamin A supplement might contain preformed vitamin A, provitamin A, or a combination of the two. See the Supplement Facts label on the container to determine the source of vitamin A in your supplement. If some of the total vitamin A comes from carotene (a provitamin A), this information will be included on the label.
Knowing how much preformed vitamin A you're taking is especially important to avoid toxicity. Taking synthetic vitamin A can lead to dangerous levels of vitamin A in your body.
Benefits of Vitamin A
Vitamin A is essential for your overall health. Most people get enough vitamin A from their diet, but people with certain medical conditions can benefit from additional vitamin A supplements.
Vitamin deficiency. Vitamin A deficiency is uncommon in developed countries, where most people get enough vitamin A from their diet. A deficiency in vitamin A can cause fatigue, eye dryness, infertility, and blindness.
Measles. Measles increases the chances of vitamin A deficiency. Giving vitamin A to children with measles reduces their risk of death.
Macular degeneration. A vitamin mix including beta-carotene slows vision loss in people with macular degeneration.
Infectious diseases. Vitamin A can be used in the treatment of several infectious diseases. It has anti-inflammatory properties and can boost your immune system.
Cancer. Vitamin A is important for cell growth, so a connection between vitamin A and cancer is plausible. However, while certain vitamin A byproducts might be useful in cancer therapy, the benefits of supplementing with vitamin A remain unclear.
Risks of Too Much Vitamin A
Taking too much vitamin A can cause negative — possibly life-threatening — side effects.
Hypervitaminosis A. Hypervitaminosis A — or vitamin A toxicity — can happen after taking a single large dose of vitamin A or taking smaller doses over a longer period of time. Symptoms include:
You shouldn't consume more than 3,000 micrograms of preformed vitamin A per day from any or all sources unless you're under the care of a doctor.
This limit doesn't apply to vitamin A that comes from carotenoids. Provitamin A from plant sources, whether in a food or supplement, doesn't carry the same risks as preformed vitamin A.
Carotenemia. If you take in too much carotene, you can develop carotenemia. Carotenemia can cause your skin to turn yellow, but it doesn't usually cause other symptoms. Even though carotene is converted to vitamin A in your body, excess carotene doesn't cause vitamin A toxicity.
Osteoporosis. Retinol intake of 1,500 micrograms of RAE or more every day might be related to osteoporosis.
Risks in pregnancy. If you're pregnant, your baby needs vitamin A for healthy growth and development. But, too much preformed vitamin A can cause birth defects in your baby. Pregnant women should avoid supplements that contain more than 1,500 micrograms of RAE.