Vitamin A


Vitamin A is a fat-soluble micronutrient that the body needs to remain healthy. Humans must obtain vitamin A or its precursors from plant and animal foods. Vitamin A is sometimes called retinol.


Vitamin A affects many different systems in the body. It is important for maintaining good vision, especially in the dark, and for a healthy immune system, growing strong bones, reproduction, and embryonic development. Vitamin A affects gene expression by helping to turn on and off specific genes during cell division and differentiation. Obtaining the correct amount of vitamin A—not too little and not too much—is essential. Vitamin A deficiency can adversely affect vision, damage the cells lining various parts of the body, and make people more susceptible to infection.

Vitamin A


Recommended dietary allowance

Tolerable upper intake level

Children 0-6 mos.

1,333 IU

400 μg

2,000 IU

600 μg

Children 7-12 mos.

1,667 IU

500 μg

2,000 IU

600 μg

Children 1-3 yrs.

1,000 IU

300 μg

2,000 IU

600 μg

Children 4-8 yrs.

1,333 IU

400 μg

3,000 IU

900 μg

Children 9-13 yrs.

2,000 IU

600 μg

5,667 IU

1,700 μg

Boys 14-18 yrs.

3,000 IU

900 μg

9,333 IU

2,800 μg

Girls 14-18 yrs.

2,333 IU

700 μg

9,333 IU

2,800 μg

Men 19≥ yrs.

3,000 IU

900 μg

10,000 IU

3,000 μg

Women 19≥ yrs.

2,333 IU

700 μg

10,000 IU

3,000 μg

Pregnant women 18≤ yrs.

2,500 IU

750 μg

9,333 IU

2,800 μg

Pregnant women 19≥ yrs.

2,567 IU

770 μg

10,000 IU

3,000 μg

Breastfeeding women 18≤ yrs.

4,000 IU

1,200 μg

9,333 IU

2,800 μg

Breastfeeding women 19≥ yrs.

4,333 IU

1,300 μg

10,000 IU

3,000 μg


Vitamin A (retinol)

Turkey giblets, cooked, V cup

25,948 IU

Beef liver, cooked, 3 oz.

22,175 IU

Chicken liver, cooked, 1 liver

2,612 IU

Skim milk, vitamin A fortified, 1 cup

500 IU

Butter, 1 tbsp.

355 IU

Cheddar cheese, 1 oz.

284 IU

Egg, 1 large

270 IU

Whole-milk yogurt, 1 cup

225 IU


Vitamin A (provitamin A carotenoid)

Sweet potato, 1 medium

28,058 IU

Pumpkin, canned, V cup

19,065 IU

Carrot, raw, unpeeled, 1 whole

12,028 IU

Spinach, frozen, cooked, V cup

11,458 IU

Kale, frozen, cooked, V cup

9,557 IU

Cantaloupe, 1 cup

5,411 IU

Red pepper, 1 cup

4,665 IU

Papaya, 1 whole

2,888 IU

Mango, 1 whole

2,240 IU

Tomato juice, 8 oz.

1,094 IU

Note: 12 mcg of beta-carotene (from provitamin A) equals 1 mcg of retinol.

1 IU equals 0.3 mcg retinol and 0.6 mcg beta-carotene.

IU = International unit

μg = microgram (mcg)

SOURCE: Office of Dietary Supplements. National Institutes of Health. “Vitamin A: Fact Sheet for Health Professionals.” U.S. Department of Health and Human Services. (accessed April 19, 2018).


Vitamin A was the first fat-soluble vitamin to be discovered. However, ancient Egyptian, Chinese, and Greek physicians all knew that eating liver could cure night blindness. In 1913, two groups of American scientists experimenting with animal feed almost simultaneously discovered an essential substance that was present in whole milk but absent from fat-free milk. They called it “fat-soluble factor A,” later vitamin A.

Close-up of a ridge in the fingernail of a 60-year-old male patient. Fingernail ridges may be caused by insufficient intake of both vitamin A and B.

Close-up of a ridge in the fingernail of a 60-year-old male patient. Fingernail ridges may be caused by insufficient intake of both vitamin A and B.
(DR P. MARAZZI/Science Source)

Vitamin A is actually a family of compounds known as retinoids, so-named because vitamin A has the biological activity of retinol, which was first isolated from the retina of the eye. Retinols are the predominant form of vitamin A in the human body. The most active retinol is 11-cis-retinol, known as preformed vitamin A. It is obtained from animal foods and is sometimes called “true” vitamin A, because it can be used directly by the body without undergoing any chemical changes. Preformed vitamin A can also be converted into retinoic acid, which is involved in controlling gene expression, and into retinal, another active form.

Plant carotenoids are also forms of vitamin A. Beta-carotene or provitamin A from plant foods is converted to active retinol in the body. Some other carotenoids, especially alpha-carotene and beta-cryptoxanthin, also can be converted into retinol by the body, although beta-carotene is converted twice as efficiently.

Vitamin A's role in health

The first function of vitamin A to be well understood was its role in vision, elucidated by Harvard scientist George Wald (1906–1997). Wald was awarded the Nobel Prize in 1967 for his work demonstrating that retinol was part of the light-absorbing pigment rhodopsin in the retina of the eye. Without enough vitamin A, the eye cannot detect low levels of light, and people with retinol deficiency develop night blindness. Night blindness disappears almost immediately when vitamin A is added to the diet. If left untreated, however, dry eye and permanent blindness can occur because of damage to the cornea, the clear covering of the eye.

Vitamin A has other important functions. It is an antioxidant that can help protect cells from the effects of free radicals that are both produced during normal metabolism and enter the body through environmental exposures such as tobacco smoke and radiation. Vitamin A is also important for the health of skin and other epithelial cells. Severe acne is sometimes treated with synthetic Vitamin A, and vitamin A supplements are often used to help burn victims grow new skin. Epithelial cells also line the throat, lungs, intestines, bladder, and other internal cavities that are the first line of defense against invading microorganisms. These cells require vitamin A to grow normally and form a continuous barrier against invasive bacteria and viruses. In addition, vitamin A is needed for the proper development of white blood cells that fight infection. Nevertheless, excess vitamin A does not appear to benefit the immune system. It remains unclear whether Vitamin A may help prevent or treat certain types of cancer.

Vitamin A requirements

The Institute of Medicine (IOM) of the U.S. National Academy of Sciences has developed dietary reference intake (DRI) values for vitamins and minerals. DRIs consist of three sets of values:

Following are the daily AIs, RDAs, and ULs in RAE (mcg) and IUs of retinol for healthy individuals:

Children who are ill may require more vitamin A. In particular, vitamin A significantly reduces the risk of complications from measles, especially eye damage and blindness, and lowers a child's risk of death from measles by 50%. The World Health Organization (WHO) recommends daily doses of 200,000 IU for two consecutive days for all children over 12 months of age with acute measles and lower doses for babies. A third dose two to four weeks later is recommended for children with clinical evidence of vitamin A deficiency.

Vitamin A from animal sources

Meat-eating Americans get about 70% of their dietary vitamin A from animal sources. Good sources of retinol include beef or chicken livers, whole eggs, whole milk, and cheese made with whole milk. Some processed foods, such as breakfast cereals and fat-free milk, are fortified with vitamin A in the form of retinol. About 80% of the dietary retinol is absorbed by the body. A portion of the vitamin A in supplements and multivitamins is usually in the form retinol.

Approximate vitamin A (retinol) contents for some common animal foods include:

Vitamin A from plant sources

Carotenoids are the pigments in yellow and orange vegetables and in some deep-green vegetables in which the orange color is obscured. Good sources of beta-carotene include carrots, cantaloupe, apricots, mango, papaya, spinach, and kale. Vegans (who do not eat any animal products) must be especially careful to get enough of these vegetables.

Approximate provitamin A carotenoid contents of some common plant foods include:


Vitamin A excess
Adequate intake (AI)—
The daily average intake level of a nutrient that is likely to be adequate for a healthy, moderately active individual, as determined by the U.S. Institute of Medicine.
Substances that prevent or reduce cellular damage from reactive oxygen species such as free radicals.
A carotenoid provitamin A in dark green and yellow fruits and vegetables that has one-twelfth the vitamin A activity of retinol.
Various common red and yellow pigments, such as beta-carotene, some of which have vitamin A and antioxidant activity.
Dietary reference intake (DRI)—
A system of nutritional recommendations used by the Institute of Medicine of the U.S. National Academy of Sciences and the U.S. Department of Agriculture.
Fat-soluble vitamin—
A vitamin that dissolves in fat and can be stored in body fat or the liver.
Free radicals—
Reactive atoms or groups of atoms that damage cells, proteins, and DNA.
International unit (IU)—
An agreed-upon standard of physiological activity for a given biological substance such as a vitamin.
A nutrient, such as a vitamin, that is required in minute amounts in the diet for growth and health.
Preformed vitamin A—
Retinol and retinyl ester that are obtained from animal sources—fish, meat (especially liver) and dairy products—and that are used directly by the body or metabolized to retinal and retinoic acid.
Provitamin A—
Carotenoids such as beta-carotene, alpha-carotene, and beta-cryptoxanthin that are converted to vitamin A in the body.
Recommended dietary allowance (RDA)—
The approximate amount of a nutrient that should be ingested daily.
Retinal and retinoic acid—
Active forms of vitamin A that are produced in the body from precursors in the diet.
Preformed vitamin A that is obtained from animal sources in the diet; the form of vitamin A that is used as the standard for determining dietary intake.
Retinol activity equivalent (RAE)—
The standard measure for vitamin A; 1 RAE is equal to 1 mcg of retinol, 12 mcg of beta-carotene, 24 mcg of other provitamin A carotenoids, or about 3 IU.
Tolerable upper intake level (UL)—
The highest daily intake level of a nutrient that is unlikely to cause adverse health effects in almost all individuals in the general population, as determined by the U.S. Institute of Medicine.

Excess vitamin A can cause birth defects. For this reason, certain prescription medications containing synthetic vitamin A should not be taken by pregnant women or women who could become pregnant.

Acute vitamin A excess usually occurs from taking large quantities of a dietary supplement. Symptoms of acute excess include nausea, vomiting, blurred vision, headache, drowsiness, and altered mental states. Chronic vitamin A excess occurs when vitamin A builds up gradually in the body. Symptoms include loss of appetite, dry skin, hair loss, insomnia, fatigue, irritability, diarrhea, menstrual irregularities, bone pain, and reduced growth rate in children.

Vitamin A deficiency (VAD)

Poor night vision, dry skin, dry hair, broken fingernails, and decreased resistance to infections are among the first signs of vitamin A deficiency. Almost all healthy people in most developed countries obtain adequate vitamin A in their normal diets to maintain health; however, certain people are at greater risk for vitamin A deficiency:

In stark contrast, VAD is a major problem in the developing world, especially in parts of Africa and Southeast Asia where famine and limited food choices often prevent people—especially children— from obtaining enough vitamin A and other nutrients. WHO estimates that more than 124 million children worldwide have a vitamin A deficiency and that one to two million children between the ages of one and four die each year from VAD. VAD is also the most common cause of childhood blindness—at least 250,000 children go blind because of VAD each year. Children with VAD are also at higher risk of dying from measles, diarrhea, malaria, and other infections. In addition to vitamin A supplements for children in the developing world, scientists are breeding and genetically engineering varieties of crops, such as rice and cassava, with increased vitamin A contents.


Vitamin A may interact with some medications and other substances:


Vitamin A is safe when taken in amounts recommended by the IOM. Too much or too little vitamin A results in serious health problems.


Parental concerns

The AIs, RDAs, and ULs for vitamin A are much lower for children than for adults. Accidental overdose can occur if children consume adult vitamins or dietary supplements.

See also ADHD diet ; African diet ; Alcohol consumption ; Antioxidants ; Arthritis diet ; Ovolactovegetarianism ; Veganism ; Vegetarianism ; Vitamins ; Vitamin toxicity ; Whole grains .



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Herrmann, Wolfgang, and Rima Obeid, eds. Vitamins in the Prevention of Human Diseases. New York: Walter de Gruyter, 2011.

Higdon, Jane, and Victoria J. Drake. An Evidence-Based Approach to Vitamins and Minerals: Health Benefits and Intake Recommendations. 2nd ed. New York: Thieme, 2012.

Ivanoff, George. Vitamins. Mankato, MN: Smart Apple Media, 2012.

Kroner, Zina. Vitamins and Minerals. Santa Barbara, CA: Greenwood, 2011.

Scott, Lucas P. Vitamin A: Nutrition, Side Effects, and Supplements. New York: Nova Science, 2011.


Ansstas, George, N. Gopalswamy, and Jigna Thakore. “Vitamin A Deficiency.” Medscape. Updated October 12, 2016. (accessed April 20, 2018).

Harvard T.H. Chan School of Public Health. “Vitamin A.” The Nutrition Source, Department of Nutrition, Harvard University. (accessed April 20, 2018).

MedlinePlus. “Vitamin A.” U.S. National Library of Medicine, National Institutes of Health. (accessed April 20, 2018).

Office of Dietary Supplements. “Fact Sheet for Health Professionals: Vitamin A.” National Institutes of Health. (accessed April 20, 2018).

U.S. Department of Agriculture, National Agricultural Library. “DRI Tables and Application Reports.” Food and Nutrition Information Center. (accessed March 15, 2018).


Academy of Nutrition and Dietetics, 120 South Riverside Plaza, Ste. 2000, Chicago, IL, 60606-6995, (312) 899- 0040, (800) 877-1600, .

Food and Nutrition Information Center, National Agricultural Library, 10301 Baltimore Ave., Rm. 105, Beltsville, MD, 20705, (301) 504-5414, Fax: (301) 504-6409,, .

Linus Pauling Institute, Oregon State University, 307 Linus Pauling Science Center, Corvallis, OR, 97331, (541) 737-5075, Fax: (541) 737-5077,, .

Office of Dietary Supplements, National Institutes of Health, 6100 Executive Boulevard, Room 3B01, MSC 7517, Bethesda, MD, 20892-7517, (301) 435-2920, Fax: (301) 480-1845,, .

Tish Davidson, AM
Revised by Margaret Alic, PhD

  This information is not a tool for self-diagnosis or a substitute for professional care.