Vitamin A

How much you need

The official Recommended Dietary Allowance for adults, per day:

Amounts are in retinol activity equivalents (RAE), which count each form by how much vitamin A the body gets from it — 1 mcg RAE is 1 mcg of retinol, 2 mcg of beta-carotene from supplements, 12 mcg of beta-carotene from food, or 24 mcg of alpha-carotene or beta-cryptoxanthin from food. Older labels used International Units (IU), which convert differently for each form, so a mixed diet's IU cannot be read off a single figure.

People aged 18 fall in the official 14–18 group — 900 mcg RAE a day for males and 700 mcg RAE for females, 750 mcg RAE in pregnancy and 1,200 mcg RAE when breastfeeding. The upper limit for preformed vitamin A in that group is 2,800 mcg. Pregnancy and breastfeeding change what you need — confirm yours with your midwife, obstetrician or doctor.

Upper limit

If you are or might be pregnant: preformed vitamin A above the upper limit can cause birth defects. Experts advise not taking supplements that provide more than 3,000 mcg RAE (10,000 IU) a day, during pregnancy or while breastfeeding. A single 3-ounce serving of beef liver provides more than twice the limit.

This limit applies only to preformed vitamin A — retinol and its esters, such as retinyl palmitate — from animal foods and supplements. It does not apply to beta-carotene or other carotenoids. For a supplement that contains both, count only the share from retinol or its esters.

The limit is the most preformed vitamin A a day, from food and supplements combined, that is unlikely to cause harm — not a target. It is in mcg of preformed vitamin A, where 1 mcg equals 1 mcg RAE. It was set from the amounts linked to liver abnormalities, birth defects and toxic effects in infants and children. No limit has been set for beta-carotene or the other carotenoids the body converts to vitamin A. One 3-ounce serving of pan-fried beef liver, the first food listed below, provides 6,582 mcg RAE, mainly as preformed vitamin A — more than twice the limit.

What it does

Vitamin A is a group of fat-soluble compounds, mainly retinol and retinyl esters ^[1]. It is involved in immune function, communication between cells, growth and development, and reproduction, and supports the normal formation and maintenance of the heart, lungs, eyes and other organs ^[1]. It is essential for vision: it is part of rhodopsin, the light-sensitive protein in the retina, and keeps the cornea and the membranes covering the eye working normally ^[1]. Most of the body's vitamin A is stored in the liver ^[1].

Forms

The diet provides vitamin A in two forms ^[1]. Preformed vitamin A — retinol and retinyl esters — is found in animal foods, including dairy products, eggs, fish and organ meats ^[1]. Provitamin A carotenoids — beta-carotene, alpha-carotene and beta-cryptoxanthin — are plant pigments that the body converts into vitamin A in the intestine, although how efficiently varies between people, partly for genetic reasons ^[1]. Other carotenoids, such as lycopene, lutein and zeaxanthin, are not converted ^[1]. In the United States, about 65% to 80% of the vitamin A people consume is preformed ^[1]. Supplements contain retinyl acetate, retinyl palmitate, beta-carotene or a mix; 3,000 mcg RAE is a common amount, and multivitamins often contain 750 to 1,050 mcg RAE ^[1].

Where it comes from

1. Beef liver, pan friedpreformed3 ounces6,582 mcg RAE
2. Sweet potato, baked in skinprovitamin A1 whole1,403 mcg RAE
3. Spinach, frozen, boiledprovitamin A½ cup573 mcg RAE
4. Pumpkin pie, commercially preparedboth forms1 piece488 mcg RAE
5. Carrots, rawprovitamin A½ cup459 mcg RAE

How these five were chosen: The five foods with the most vitamin A per serving in the NIH fact sheet's food table. Fortified foods are marked.

Getting the most from it

The body may absorb 75% to 100% of the retinol in food but, in most cases, only 10% to 30% of the beta-carotene ^[1]. Cooking and heat treatment can make the beta-carotene in food more available ^[1]. From supplements, 70% to 90% of preformed vitamin A is absorbed, and 8.7% to 65% of beta-carotene ^[1]. Vitamin A is routinely added to some foods, including milk and margarine, and some ready-to-eat cereals are fortified with it ^[1].

In the United States

In national survey data from 2017–2018, average intake from food and drink was 682 mcg RAE a day for men aged 20 and older and 616 mcg RAE for women ^[1]. Even so, fewer than 1% of Americans have a blood retinol level below 20 mcg/dL, so deficiency is uncommon ^[1]. In data from 1988–1994, about 26% of the vitamin A men consumed and 34% of what women consumed came from carotenoids, and the rest from preformed vitamin A, mostly retinyl esters ^[1]. About 12% to 40% of people, depending on age, take a supplement containing vitamin A; adults 71 and older are among the most likely to ^[1].

Who is most likely to run low

• Pregnant and breastfeeding women in low- and middle-income countries — pregnancy raises the need for vitamin A, and about 10% to 20% of pregnant women in low-income countries are deficient ^[1]
• People with cystic fibrosis — up to 90% have pancreatic insufficiency, which makes fat, and with it vitamin A, hard to absorb ^[1]
• People with Crohn's disease or ulcerative colitis, especially those who have had the disorder for several years ^[1]
• Some people with newly diagnosed celiac disease; a gluten-free diet can, but does not always, correct the deficiency ^[1]

What deficiency looks like

Frank deficiency is rare in the United States but still common in many low-income countries ^[1]. Its most common sign is xerophthalmia, and the first symptom is night blindness — difficulty seeing in low light or darkness — caused by low levels of rhodopsin in the retina ^[1]. Xerophthalmia also damages the cornea and can end in permanent blindness; vitamin A deficiency is one of the top causes of preventable blindness in children ^[1]. Chronic deficiency is also linked to respiratory diseases such as pneumonia, anemia, and more severe and deadly infections, particularly measles and diarrhea ^[1]. Blood retinol does not fall until the liver's stores are almost depleted, but a level of 20 mcg/dL or less often reflects moderate deficiency, and 10 mcg/dL or less severe deficiency ^[1].

What the evidence supports, and what it doesn't

Established. Vision, immune function, growth and reproduction depend on vitamin A, and night blindness is the first sign of deficiency ^[1]. Deficiency is one of the top causes of preventable blindness in children ^[1].

Not supported by trials. Cancer prevention. Among nonsmokers, beta-carotene and vitamin A supplements do not appear to affect the risk of cancer ^[1]. In smokers they have done harm. In CARET, 18,314 current and former smokers and asbestos-exposed workers aged 45–74 took 30 mg beta-carotene plus 7,500 mcg RAE (25,000 IU) retinyl palmitate a day or a placebo; the trial was stopped early, after a mean of 4 years, when lung cancer was 28% higher, lung cancer deaths 46% higher and deaths from all causes 17% higher ^[1]. In ATBC, 29,133 male smokers aged 50–69 who took 20 mg beta-carotene a day for 5 to 8 years had 18% more lung cancer and an 8% higher death rate ^[1]. In AREDS2, in which no current smokers were given beta-carotene, more lung cancers occurred in the beta-carotene group (23 against 11), 31 of the 34 in former smokers ^[1]. Three other trials, with smaller shares of smokers, found no effect on lung cancer ^[1].

Mixed. Age-related macular degeneration: in AREDS, people at high risk of advanced AMD who took a daily supplement of beta-carotene (15 mg), vitamins C and E, zinc and copper for 5 years had a 25% lower risk of advanced AMD than those on placebo ^[1]. AREDS2 found the formula protected as well without beta-carotene, and replacing it with lutein and zeaxanthin lowered the risk of progression further ^[1]. The fact sheet advises people who have or are developing AMD to talk to their health care provider about the AREDS formulations ^[1]. Other cancers: observational studies link higher intakes of retinol, carotenoids, or fruit and vegetables with lower risk of several cancers, while others find no link ^[1]. Measles: in a 2022 Cochrane review, six trials in 19,566 children aged 6 months to 5 years in low- and middle-income countries found that high-dose vitamin A halved new cases of measles, but six trials in more than a million children found no effect on deaths from measles ^[1].

Too much

Because vitamin A is fat-soluble, the body stores the excess, mainly in the liver ^[1]. One or a few very high doses — typically more than 100 times the recommended amount — cause acute toxicity within days to weeks: severe headache, blurred vision, nausea, dizziness, aching muscles and poor coordination, and in severe cases raised fluid pressure around the brain, drowsiness, coma and death ^[1]. Regular high doses cause dry skin, painful muscles and joints, fatigue, depression and abnormal liver test results ^[1]. Total intakes of preformed vitamin A above the upper limit can cause birth defects of the eye, skull, lungs and heart, and experts advise women who are or might be pregnant, and those who are breastfeeding, not to take supplements providing more than 3,000 mcg RAE (10,000 IU) a day ^[1]. Beta-carotene is not known to cause birth defects; too much over a long time turns the skin yellow-orange, a harmless condition that reverses when intake stops ^[1]. Even so, the Food and Nutrition Board advises against beta-carotene supplements for the general population, except as a source of vitamin A to prevent deficiency ^[1].

Medicines that interact

Orlistat (Alli, Xenical), a weight-loss drug, reduces the absorption of vitamin A, beta-carotene and the other fat-soluble vitamins, and its makers recommend a multivitamin that contains them ^[1]. Synthetic retinoids taken by mouth — such as acitretin (Soriatane) for psoriasis and bexarotene (Targretin) for the skin effects of T-cell lymphoma — can raise the risk of vitamin A toxicity when combined with vitamin A supplements ^[1]. If you take any of these regularly, talk to your doctor or pharmacist before taking a vitamin A supplement.