Vitamin A: Functions and Role in the Body

Vitamin A is one of the most underestimated nutrients, whose deficiency often hides behind symptoms that people typically attribute to stress or fatigue. Difficulty seeing in low light, frequent colds, dry and flaking skin — all of these may point specifically to a lack of vitamin A. According to the WHO, vitamin A deficiency remains one of the most widespread forms of nutritional deficiency worldwide, particularly among children and women of reproductive age.

Vitamin A is essential for hundreds of biological processes: from supporting the visual system to regulating immune response and cell differentiation. Without it, normal fetal development, healthy skin and mucous membranes, and proper thyroid function are all impossible. It is not merely a “vitamin for the eyes” — it is one of the key regulators in the body’s health maintenance chain.

In this article, you will learn about all the key functions of vitamin A, daily norms for different population groups, signs and consequences of deficiency and excess, the best food sources, and practical supplement advice.

What Is Vitamin A and Why Is It Essential

Vitamin A is a fat-soluble vitamin that exists in two main forms. The first — retinol and its derivatives (retinal, retinoic acid) — is found exclusively in animal-based foods and is absorbed directly by the body. The second — provitamin A, primarily beta-carotene — comes from plant foods and is converted into retinol in the wall of the small intestine, though significantly less efficiently. The human body cannot synthesize vitamin A on its own, so its supply depends entirely on diet or supplements.

Vitamin A is commonly — and mistakenly — associated only with eye health. In reality, it regulates the expression of over 500 genes and participates in processes related to cell growth, immunity, reproduction, and the maintenance of epithelial tissue integrity throughout the body. That is why its deficiency is systemic in nature and affects several organs and systems at once.

Unlike similar nutrients — such as vitamin D — vitamin A’s active form (retinoic acid) acts as a nuclear ligand, directly influencing gene transcription. This makes it one of the most important regulators of cellular development and differentiation.

Vitamin A Daily Norms

*RAE — retinol activity equivalent. 1 mcg RAE = 1 mcg retinol = 12 mcg beta-carotene from food. Source: NIH Office of Dietary Supplements.

To meet the daily norm for a woman (700 mcg RAE), it is enough to eat 80 g of carrots or a small piece of beef liver (about 30 g). However, covering the norm exclusively from plant sources is more challenging — due to the low efficiency of beta-carotene conversion to retinol. People with inflammatory bowel diseases, celiac disease, or those following a vegan diet should monitor their vitamin A levels more carefully.

Functions and Role of Vitamin A in the Body

Vitamin A and Vision — How They Are Connected

Retinal — a direct derivative of vitamin A — is an essential component of rhodopsin, the light-sensitive pigment in the retina’s rod cells. Rods are responsible for twilight and peripheral vision. When a photon of light hits the retina, rhodopsin breaks down, triggering a nerve impulse. Retinal then needs to be “recharged” — and this requires a constant supply of vitamin A. When it is insufficient, the rhodopsin restoration process slows down, and the person begins to see poorly in dim lighting — this is night blindness, or nyctalopia.

Beyond night vision, vitamin A supports the health of the conjunctiva and cornea by stimulating the production of mucin — the protective mucus that moistens the eye surface. With chronic deficiency, xerophthalmia develops: the eyes become dry, sensitivity to light appears, and in severe cases — corneal ulcers and irreversible vision loss.

Role in Supporting Immunity

Vitamin A plays a key role in two levels of immune defense simultaneously. First, it maintains the integrity of mucous membranes — the first barrier against pathogens. Retinoic acid stimulates the differentiation of epithelial cells and the production of protective mucus in the respiratory tract, digestive system, and genitourinary system. Second, vitamin A directly influences cellular immunity: it is needed for the maturation and proliferation of T-lymphocytes, NK cells, and macrophages.

Research has shown that children with vitamin A deficiency face significantly higher risks of severe infectious diseases — including measles, pneumonia, and diarrhea. The WHO recommends vitamin A supplementation for children in regions with widespread deficiency specifically because of its impact on mortality from infections.

Effect on Skin and Mucous Membranes

Skin is one of the most visible “indicators” of vitamin A levels. Retinoic acid regulates the growth and differentiation of keratinocytes — the main cells of the epidermis. At sufficient levels of vitamin A, skin remains elastic, moisturized, and heals minor damage well. With deficiency, hyperkeratosis appears — excessive keratinization that presents as dry, rough skin with small bumpy eruptions, particularly on the shoulders and thighs (known as “goose skin” or follicular keratosis).

This same mechanism underpins dermatological preparations based on retinol and retinoic acid, used to treat acne, photoaging, and certain dermatoses — but at doses far exceeding dietary levels, and exclusively under medical supervision.

Role in Fetal Development and Reproductive Health

During pregnancy, vitamin A participates in the formation of the heart, lungs, kidneys, eyes, ears, and the skeletal and nervous systems of the fetus. Retinoic acid is a potent morphogen — it defines the “body plan” in the early stages of embryogenesis. At the same time, pregnant women must be particularly cautious: excess vitamin A (more than 3,000 mcg RAE per day) in retinol form has been shown to increase the risk of congenital fetal malformations.

Beta-carotene from plant products does not carry this risk — the body regulates its conversion to retinol based on need. Therefore, pregnant women are advised to meet their vitamin A needs primarily through vegetables and fruits, and to avoid retinol supplements at doses exceeding the pregnancy norm.

Vitamin A and Cell Growth: Connection to Oncology

Retinoic acid regulates the cell division cycle and apoptosis (programmed cell death). These properties have attracted research interest in the context of cancer prevention. Observational studies suggest a link between adequate vitamin A levels and lower risk of certain cancers — particularly lung cancer in non-smokers. However, it is important to understand: beta-carotene supplements in smokers in one large study (CARET) were associated with an increased — not decreased — risk of lung cancer. This is a clear example that “more” does not mean “better,” and that the context of supplementation is critically important.

Role in Supporting Bone Tissue

Vitamin A influences the activity of osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells), so its balance matters for skeletal health. Interestingly, both deficiency and excess of vitamin A can reduce bone density. Some studies have found a link between chronically elevated retinol intake and increased risk of hip fractures, particularly in people with insufficient vitamin D. Therefore, when taking vitamin A supplements, it is important to also maintain adequate vitamin D levels.

Signs and Consequences of Vitamin A Deficiency

Eye Symptoms — Early Warning Signs

The earliest and most specific symptom of vitamin A deficiency is night blindness: difficulty orientating in the dark or when moving from a brightly lit to a poorly lit area. This occurs because restoring rhodopsin after each photochemical cycle requires retinal — and when it is lacking, the restoration process slows. If the deficiency is not corrected, xerophthalmia develops — dryness of the conjunctiva, then the cornea — which can lead to blindness. This form of blindness is preventable: it is fully reversible in early stages with timely vitamin A replenishment.

Risk: particularly relevant for children under 5 years, people with GI disorders (Crohn’s disease, celiac disease), and those following a strict plant-based diet without attention to vitamin A forms. Practical recommendation: if you notice symptoms of impaired twilight vision, see an ophthalmologist and get a blood test for serum retinol levels.

Skin, Immunity, and Other Systemic Manifestations

Follicular keratosis (rough “goose skin” on shoulders and thighs), dry skin and mucous membranes, flaking — these are typical manifestations of moderate deficiency. Simultaneously, the barrier function of the mucous membranes of the respiratory tract and intestine decreases, leading to more frequent respiratory infections, diarrhea, and slow wound healing. In children, chronic vitamin A deficiency is associated with an increased risk of severe measles and pneumonia.

At-risk groups include: infants and young children (especially on a meager diet), pregnant and breastfeeding women (increased need), people with fat malabsorption (pancreatitis, cholestasis, cystic fibrosis, chronic pancreatic or gallbladder diseases), and those following a strict vegan diet without nutrient monitoring. If symptoms are present — consult a doctor and check serum retinol levels in the blood.

Vitamin A Excess — When There Is Too Much

Acute and Chronic Hypervitaminosis

Unlike water-soluble vitamins, vitamin A accumulates in the liver, and its excess is toxic. Acute hypervitaminosis occurs with a single intake of very large doses (over 100,000 IU in adults) and manifests as nausea, vomiting, dizziness, headache, and skin peeling. Chronic hypervitaminosis develops with prolonged exceeding of the upper safe limit (3,000 mcg RAE/day for adults) and can cause joint pain, hair loss, liver damage, and increased intracranial pressure.

Excess is only possible through supplements or injections — it is practically impossible to reach a toxic dose through food, with the exception of regularly consuming large portions of beef liver. Important: excess beta-carotene from plant products does not cause hypervitaminosis — the worst that can happen is carotenodermia (a yellowish tint to the skin), which is harmless and disappears after reducing intake.

Pregnancy and Vitamin A: Special Caution Required

The teratogenic effect of vitamin A in retinol form is well established: daily doses exceeding 3,000 mcg RAE during pregnancy are associated with a risk of congenital defects of the heart, neural tube, and facial skeleton in the fetus. Therefore, pregnant women are advised not to take retinol supplements above the established norm (770 mcg RAE), and to avoid synthetic retinoids in any form. This also applies to isotretinoin-based medications — they are contraindicated during pregnancy. When planning a pregnancy, discuss any supplements with your doctor in advance.

Who Should Pay Special Attention to Vitamin A Levels

Young Children

Children under 5 have a relatively high need for vitamin A due to active growth, visual development, and immune system formation, while their diet is often limited. The WHO recommends vitamin A supplementation for children in regions with widespread deficiency. Parents should ensure that carrots, pumpkin, sweet potato, or egg yolk are regularly included in the child’s diet. If deficiency is suspected — consult a pediatrician.

Pregnant and Breastfeeding Women

The need for vitamin A during pregnancy increases to support fetal development, and during breastfeeding it increases even further, as the vitamin is transferred to the baby through milk. At the same time, excess retinol is dangerous. The optimal strategy: meet the need primarily through plant sources of beta-carotene and a balanced diet, and take supplements only as prescribed by a doctor.

People with Fat Malabsorption

Since vitamin A is fat-soluble, any condition that disrupts fat absorption in the intestine leads to its deficiency: Crohn’s disease, celiac disease, cystic fibrosis, chronic pancreatic or gallbladder diseases, and conditions following bariatric surgery. This group is advised to regularly check serum retinol levels and discuss the need for supplementation with their doctor.

People Following a Vegan Diet

A vegan diet does not contain ready-formed retinol — only the provitamin beta-carotene. The efficiency of its conversion to retinol varies depending on genetic factors (BCMO1 gene polymorphisms), gut health, and fat content in the diet. If your diet is rich in colorful vegetables and fruits and includes sufficient fats — the risk of deficiency is low. However, if symptoms appear, it is worth checking retinol levels.

Older Adults (60+)

With age, the efficiency of absorbing many nutrients decreases — especially in the presence of chronic GI diseases or when taking certain medications. At the same time, older adults are more likely to take supplements without monitoring, which increases the risk of accumulating toxic doses of retinol. It is recommended not to exceed the daily norm without medical consultation and to prefer beta-carotene sources.

Best Food Sources of Vitamin A

Vitamin A in retinol form is found exclusively in animal-based products, while plant foods provide the provitamin beta-carotene. Here are the richest sources:

Source: USDA FoodData Central. Values are approximate and may vary by variety, storage conditions, and preparation.

Important: heat processing generally preserves vitamin A well — it is stable under moderate boiling and baking temperatures. However, prolonged storage with exposure to oxygen and light degrades beta-carotene in plant products.

Best Combinations for Better Absorption

Vitamin A is fat-soluble — so its absorption directly depends on the presence of fats in food. Carrots or sweet potato eaten with a small amount of oil or avocado will provide significantly better bioavailability of beta-carotene than the same foods without fat. Synergy with vitamin D and zinc: zinc is necessary for the synthesis of retinol-binding protein, which transports vitamin A in the blood. With zinc deficiency, even adequate vitamin A intake may not produce the expected effect. Vitamin E acts as an antioxidant, protecting vitamin A from oxidation. Conversely, excess iron and excessive alcohol consumption disrupt vitamin A metabolism in the liver.

Vitamin A Supplements — When Are They Needed

Vitamin A supplements are justified in several situations: confirmed deficiency by blood test (serum retinol level < 0.7 micromol/L), pregnancy in women at risk of deficiency (as prescribed by a doctor), diseases that impair fat absorption, and in children in regions with widespread deficiency (on a pediatrician’s recommendation).

Forms of supplements: retinol palmitate and retinol acetate — the most common forms, well absorbed. Beta-carotene — a safer alternative (no risk of hypervitaminosis), but less effective with genetic variants of reduced conversion. Vitamin A should be taken with fat-containing food — this improves absorption. Avoid taking on an empty stomach.

Important note: supplements are a complement, not a replacement, for a balanced diet. Before starting supplementation — always consult a doctor, especially if you are pregnant, have liver disease, or take other medications. Do not exceed the upper safe limit (3,000 mcg RAE per day for adults) without medical supervision.

Common Myths About Vitamin A

“Carrots give you eagle-eye vision”

This myth did not arise from nothing — it is partly linked to British wartime propaganda during World War II, where carrots were credited for the extraordinary night-interception accuracy of the RAF (concealing the existence of radar). This cemented the idea of a “vision vitamin” in popular consciousness.

The reality is somewhat more modest: vitamin A is indeed critically important for normal night vision, and its deficiency leads to deterioration of twilight vision. But if you have no deficiency — eating more carrots will not make your vision sharper than normal. Vitamin A corrects the consequences of deficiency, but it is not a “vision booster” for healthy people.

“Beta-carotene in supplements is a safe alternative to retinol”

This myth spread through a logical but not always correct chain: beta-carotene converts to retinol, so beta-carotene supplements are a safe and effective alternative. However, the CARET and ATBC studies showed that in smokers and people exposed to asbestos, taking beta-carotene supplements at high doses (20–30 mg/day) was associated with an increase — not a decrease — in lung cancer risk and mortality.

This does not mean that beta-carotene from food is harmful — in whole food it is safe. The problem lies in megadoses in the form of isolated supplements under certain conditions. The solution is simple: get beta-carotene from vegetables and fruits, and take supplements only when needed and at recommended doses.

“Vitamin A boosts immunity — so take more during cold season”

The logic seems convincing: vitamin A supports immunity — so more vitamin A equals better immunity. In reality, the immune system requires balance. Vitamin A is indeed important for normal immune cell function, but excess can have the opposite effect — it influences T-cell differentiation, and with chronically elevated intake may disrupt rather than enhance the immune response.

Moreover, if you are not deficient, additional doses provide no immune benefit. It is far more effective to focus on a varied diet with sufficient vegetables and fruits, adequate sleep, and moderate physical activity.

Conclusion

Vitamin A is an essential nutrient with a wide range of functions: from supporting vision and immunity to regulating cell growth and skin condition. Its balance in the diet is important at any age, but especially so for children, pregnant women, and people with digestive disorders.

A practical step for today: check whether your diet regularly includes sources of vitamin A — carrots, sweet potato, pumpkin, egg yolk, or small portions of liver once a week. If you notice signs of deficiency or belong to a risk group — consult a doctor and test your retinol levels before self-prescribing supplements.

Remember: vitamin A is a powerful regulator, and the “more is better” principle does not apply here. An optimal level, not a maximum one — that is the key to health.