Vitamins

Vitamin A

By All The Nutrients Editorial Team Published: 9 min read

Vitamin A is a fat-soluble vitamin that exists in two principal forms in the diet: preformed vitamin A (retinol and retinyl esters, from animal foods) and provitamin A carotenoids (beta-carotene, alpha-carotene, beta-cryptoxanthin, from plant foods) that the body converts to retinol as needed. It plays irreplaceable roles in vision, immune defence, cellular differentiation, and reproduction. Globally, vitamin A deficiency is the leading cause of preventable childhood blindness and significantly increases child mortality from measles and diarrhoea — affecting an estimated 190 million preschool-aged children in developing regions. See the top food sources of vitamin A ranked by concentration.

Daily Value

900 ug

FDA 2020

Upper Limit

3000 ug

per day

Top Source

Fish oil, cod liver

30000 ug

What Does Vitamin A Do?

  • Vision and night adaptation — retinal (an aldehyde form of retinol) combines with the protein opsin to form rhodopsin in rod cells, enabling vision in dim light. Vitamin A deficiency impairs rhodopsin regeneration, causing night blindness — the earliest clinical sign of deficiency. Sustained deficiency causes xerophthalmia (dryness and inflammation of the conjunctiva and cornea), which can progress to corneal ulceration and irreversible blindness.
  • Immune function and infection resistance — retinoic acid (the acid form of vitamin A) regulates the differentiation of immune cells including T helper cells, dendritic cells, and IgA-secreting B cells. It is essential for maintaining the integrity of epithelial barriers in the gut, lungs, and skin — the body's first line of defence. Vitamin A deficiency dramatically increases susceptibility to and mortality from measles, diarrhoea, and respiratory infections; supplementation in deficient children reduces all-cause mortality by 24% (Cochrane 2011).
  • Cell growth, differentiation, and gene expression — retinoic acid binds to nuclear receptors (RARα, RARβ, RARγ) that regulate the expression of hundreds of genes involved in cell differentiation, proliferation, and apoptosis. This function is essential for embryonic development and organogenesis, and underpins vitamin A's role in tissue maintenance throughout life.
  • Skin and epithelial health — vitamin A promotes keratinocyte differentiation and mucus-secreting cell production in all epithelial tissues (skin, gut lining, respiratory tract, reproductive tract). Deficiency causes keratinisation of mucous membranes, impairing barrier function. Topical retinoids (tretinoin, adapalene) are clinically proven treatments for acne and photoageing.
  • Reproduction and foetal development — retinoic acid is required for spermatogenesis in males and ovulation in females. During pregnancy, it is critical for heart, eye, ear, and limb formation. However, preformed vitamin A at doses exceeding 3,000 mcg RAE/day is teratogenic — causing craniofacial malformations — making provitamin A carotenoids from food the safer source during pregnancy.
Horizontal bar chart: beef liver 6582 mcg RAE per 85g, sweet potato baked 961 mcg per medium, carrots raw 835 mcg per 100g, butternut squash cooked 532 mcg per 100g, spinach cooked 573 mcg per 100g, fortified milk 150 mcg per cup, egg 80 mcg per large. FDA DV reference line at 900 mcg RAE.
Liver is by far the richest vitamin A source; one serving exceeds the weekly need. Plant sources provide provitamin A (beta-carotene), absorbed more efficiently when cooked and eaten with fat.
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Signs of Vitamin A Deficiency

Vitamin A deficiency is the leading cause of preventable childhood blindness worldwide and a major contributor to child mortality in sub-Saharan Africa and South Asia. In high-income countries, deficiency is uncommon in the general population but occurs in groups with fat malabsorption conditions (Crohn's disease, cystic fibrosis, coeliac disease, cholestatic liver disease), very low-fat diets, chronic alcohol use, or zinc deficiency (zinc is required to transport retinol from the liver). Night blindness is the first clinical sign; the full progression (xerophthalmia) is irreversible if untreated.

  • Night blindness (nyctalopia) — difficulty seeing in dim light or adjusting from bright to dark environments; the earliest and most sensitive sign
  • Dry eyes and Bitot's spots — white foamy patches on the conjunctiva caused by keratin buildup; a diagnostic sign of deficiency
  • Corneal ulceration and keratomalacia — in severe, prolonged deficiency; can result in permanent blindness
  • Dry, rough, or bumpy skin (follicular hyperkeratosis) — caused by impaired keratinocyte differentiation; skin feels like sandpaper
  • Increased frequency and severity of infections — particularly measles, diarrhoea, and respiratory infections; immune impairment precedes clinical eye signs
  • Impaired wound healing — epithelial repair requires adequate retinol
  • Poor growth in children — vitamin A is required for bone remodelling and normal childhood development
  • Reproductive problems — infertility or impaired sperm production in severe deficiency

Upper Limit: The Tolerable Upper Intake Level (UL) for preformed vitamin A is 3,000 mcg RAE/day for adults. Pregnant women are advised to keep intake below 3,000 mcg RAE/day from all sources to avoid teratogenic risk; most prenatal supplements contain 770 mcg RAE or less. Beta-carotene and other provitamin A carotenoids from food do not contribute to vitamin A toxicity.

Consider supplementing

Vitamin A supplement

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How to Get the Most from Vitamin A

Vitamin A absorption is strongly influenced by dietary fat and food matrix. Preformed vitamin A (retinyl esters from animal foods) is highly bioavailable — approximately 70–90% absorbed. Provitamin A carotenoids from plant foods are far less efficient: approximately 12 mcg of beta-carotene from food = 1 mcg RAE, though bioavailability varies widely (3–27%) depending on the food matrix, cooking, and individual genetics (BCMO1 enzyme polymorphisms). Vitamin A is stored in the liver (90% of body stores) and released as retinol bound to retinol-binding protein (RBP) — a process that requires adequate zinc and protein status.

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Always eat carotenoid-rich foods with fat

Beta-carotene and other provitamin A carotenoids are fat-soluble and require dietary fat for absorption. Studies show that adding as little as 3–5 g of fat to a meal (approximately 1 teaspoon / 5 mL of oil) increases carotenoid absorption by 3–5x compared to a fat-free meal. Cooking vegetables in oil or pairing them with a fat source (avocado, olive oil, eggs) is nutritionally advantageous.

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Cook and mash carotenoid-rich vegetables

Heat breaks down plant cell walls that trap carotenoids in chromoplasts, making them more accessible. Cooked, pureed, or mashed carrots have 3–5x greater beta-carotene bioavailability than raw. Chopping and cooking also ruptures carotenoid-containing chromoplasts in the food matrix, dramatically improving absorption.

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Preformed vitamin A (retinol) needs no conversion — but avoid megadosing during pregnancy

Preformed vitamin A from liver and fortified foods is directly usable without conversion. However, because it accumulates in the liver and is teratogenic at high doses, pregnant women should avoid liver consumption more than once a week and should not take vitamin A supplements beyond standard prenatal doses (which contain 770 mcg RAE or less). Beta-carotene from food does not cause toxicity because conversion is downregulated when stores are adequate.

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Adequate zinc is required for vitamin A mobilisation

Zinc is needed for the synthesis of retinol-binding protein (RBP), which transports retinol from the liver to tissues. Zinc deficiency can cause symptoms of vitamin A deficiency even when liver stores are adequate. People with low zinc status (common in those on plant-predominant diets, elderly adults, or those with malabsorption conditions) should ensure adequate zinc alongside vitamin A.

Common Vitamin A Questions

What does vitamin A do in the body?

Vitamin A serves three broad roles: (1) Vision — retinal combines with opsin to form rhodopsin in rod cells for dim-light vision; deficiency causes night blindness. (2) Immune defence — retinoic acid maintains epithelial barrier integrity in the gut, lungs, and skin, and regulates immune cell differentiation; deficiency increases susceptibility to measles, respiratory infections, and diarrhoea. (3) Cell differentiation and gene expression — retinoic acid binds nuclear receptors (RAR/RXR) that regulate hundreds of genes involved in embryonic development, tissue maintenance, and reproduction. Vitamin A is also required for normal bone growth, red blood cell production, and reproductive function.

What are the signs of vitamin A deficiency?

The earliest sign is night blindness — difficulty seeing in dim light or after moving from a bright environment. As deficiency progresses, the conjunctiva and cornea dry out (xerophthalmia); white foamy patches (Bitot's spots) appear on the conjunctiva. Severe, prolonged deficiency causes corneal ulceration and keratomalacia, which can lead to permanent blindness. Skin becomes dry and rough (follicular hyperkeratosis, sometimes described as "toad skin"). Immune function deteriorates, increasing susceptibility and mortality from measles, diarrhoea, and respiratory infections. Globally, vitamin A deficiency affects approximately 190 million preschool-aged children and is the leading cause of preventable childhood blindness.

How much vitamin A do I need per day?

The FDA Daily Value for vitamin A is 900 mcg RAE (retinol activity equivalents). The National Academies RDA is 900 mcg RAE/day for adult men and 700 mcg RAE/day for adult women. Pregnant women need 770 mcg RAE/day; breastfeeding women need 1,300 mcg RAE/day. The Tolerable Upper Intake Level (UL) from preformed vitamin A is 3,000 mcg RAE/day for adults — exceeding this long-term from supplements or frequent liver consumption risks liver toxicity and, in pregnancy, birth defects. Provitamin A carotenoids from food do not contribute to toxicity.

What foods are highest in vitamin A?

The richest preformed vitamin A source is beef liver — a single 85 g (3 oz) serving provides approximately 6,582 mcg RAE, more than 7× the daily value. Other liver sources (chicken liver, pork liver) also provide very high amounts. The richest plant sources of provitamin A (beta-carotene) per 100 g are sweet potato baked (961 mcg RAE), carrots raw (835 mcg RAE), and butternut squash (532 mcg RAE). Spinach, kale, and other dark leafy greens are good sources, as are red and orange bell peppers. Fortified dairy products (milk, cheese) and eggs provide moderate preformed vitamin A.

Is beta-carotene the same as vitamin A?

No — beta-carotene is a provitamin A carotenoid that the body converts to retinol (vitamin A) in the small intestine and liver, but the conversion is inefficient. On average, 12 mcg of dietary beta-carotene yields 1 mcg of retinol activity equivalent (RAE). This 12:1 ratio reflects the fact that: (1) not all beta-carotene is absorbed (bioavailability ranges from 3–27% depending on food matrix, cooking, and fat content), and (2) the BCMO1 enzyme that converts beta-carotene to retinol varies by individual genetics — some people are "poor converters." Preformed vitamin A (retinol) from liver, dairy, and fortified foods is directly usable at essentially 1:1 efficiency. Beta-carotene from food does not cause vitamin A toxicity because conversion is regulated according to body needs.

Can vitamin A be toxic?

Yes — preformed vitamin A (retinol) is fat-soluble and accumulates in the liver, where high doses cause toxicity. Acute toxicity (from a single very large dose, typically from supplements) causes nausea, vomiting, dizziness, and blurred vision. Chronic toxicity from long-term supplement use above 3,000 mcg RAE/day causes liver damage, bone loss (paradoxically, despite vitamin A's role in bone), hair loss, and skin changes. Most critically, preformed vitamin A is teratogenic: doses above 3,000 mcg RAE/day in early pregnancy cause craniofacial malformations, heart defects, and central nervous system abnormalities. Pregnant women should avoid liver more than once weekly and high-dose vitamin A supplements. Beta-carotene from food is not toxic — excess causes carotenodermia (orange skin discolouration) which is harmless and reversible.