Vitamin A
A fat‑soluble nutrient supporting vision, skin integrity and immune function.
Vitamin A is a fat-soluble micronutrient that includes retinol, retinal and retinoic acid. It occurs in animal foods such as liver, fish oils, dairy and eggs and as provitamin A carotenoids (for example beta‑carotene) in many vegetables; it cannot be synthesized by the human body and is stored in the liver and adipose tissue. The nutrient is involved in visual function, antioxidant activity, maintenance of skin and mucosal integrity, and the regulation and differentiation of immune cells.
Recommended intakes vary by age and sex and are commonly expressed as retinol equivalents (RE); 1 µg retinol = 1 RE ≈ 3.3 IU. Vitamin A is supplied in dietary supplements as softgels, tablets or oil solutions, but supplementation carries safety considerations: excessive intake can cause skin dryness and hair thinning and may increase teratogenic risk in pregnancy; supplemental preformed vitamin A is not advised for smokers and supplementation can be contraindicated in lactation, chronic fat-malabsorption disorders or with certain medications. Uses and effects may vary by individual; seek personalized advice from a qualified healthcare professional when considering supplementation.
At a Glance
A fat‑soluble micronutrient found in animal and plant sources, Vitamin A comprises retinol, retinal and retinoic acid and is stored in the liver and adipose tissue.
It contributes to visual function, antioxidant protection, maintenance of skin and mucosal integrity, and regulation of immune cell differentiation.
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| Classification | Liposoluble vitamin |
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Origin & History
Vitamin A is sourced from both animal and plant foods: preformed vitamin A (retinoids) is abundant in liver, fish oils, dairy and eggs, while provitamin A carotenoids are present in vegetables such as carrots and leafy greens. It is a fat‑soluble nutrient stored in the liver and adipose tissue and has been incorporated into traditional diets worldwide through consumption of organ meats and oil‑rich foods.
Ancient medical writers documented a form of vision impairment later linked to dietary deficiency, and subsequent scientific work identified vitamin A as the fat‑soluble compound responsible for these effects. Liver and other animal fats have long been used in many cultures as traditional remedies for poor vision and general nourishment.
Composition & Active Compounds
Vitamin A exists in three principal chemical forms—retinol, retinal and retinoic acid—and is a fat‑soluble group of isoprenoid-derived molecules. These compounds include alcohol, aldehyde and acidic structures; plant-derived provitamin A carotenoids such as beta‑carotene are pigments that can be converted into retinol by the body.
Retinol and its conversion to retinoic acid are central to vitamin A’s biological activity.
- Retinol: alcohol form and storage/transport precursor
- Retinal: aldehyde form involved in the visual cycle
- Retinoic acid: active acidic form that regulates cell differentiation and gene expression
- Beta‑carotene: provitamin A carotenoid converted to retinol and acts as an antioxidant precursor
- Other carotenoids: plant pigments serving as provitamins or antioxidants
Related Herbs
Properties & Effects
Vitamin A is traditionally recognized for supporting visual health, maintaining skin and mucosal barriers, and contributing to normal immune function. It is a fat‑soluble nutrient obtained from animal foods and from plant carotenoids that the body can convert to active forms.
Its role in vision is the most well-documented and historically noted function.
- Antioxidant: May support protection of cells and membranes from oxidative stress.
- Immunity: May support regulation and differentiation of immune cells and normal immune responses.
- Vision: May support normal visual function, particularly low‑light or night vision.
- Skin integrity: May support maintenance of healthy skin and mucous membranes and barrier function.
- Energy metabolism: May contribute to processes involved in normal energy metabolism.
Dosage & How to Use
Dosage guidance is based on recommended intakes and standard unit conversions.
| Recommended intake | 400–1000 RE (varies by age and sex) |
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Safety, Side Effects & Contraindications
Certain people should avoid high-dose or supplemental preformed vitamin A and take precautions when considering supplementation. Smokers, pregnant women or those planning pregnancy, individuals who are breastfeeding, and people with chronic fat‑malabsorption disorders or taking therapies that alter vitamin A absorption should be particularly cautious because supplementation may carry specific risks or be contraindicated.
Excess vitamin A intake can cause symptoms such as dry skin, chapped lips, itching and hair thinning; effects vary by individual and depend on dose and duration. Interactions with some medications or therapies that interfere with absorption have been reported, so discuss supplementation with a qualified healthcare professional if there are existing medical conditions, pregnancy, lactation, or concurrent drug treatments.
- Smokers: Supplemental vitamin A is not recommended for people who smoke because it may become pro‑inflammatory under cigarette smoke exposure and is associated with increased lung cancer risk.
- Pregnancy: Excess intake may increase the risk of fetal malformations; avoid high‑dose supplements and follow recommended intakes.
- Lactation: Supplementation can be contraindicated during breastfeeding.
- Chronic fat‑malabsorption: Supplements containing vitamin A are not suitable in chronic intestinal malabsorption or lipid absorption disorders.
- Medications/therapies: Certain medications or treatments that interfere with vitamin A absorption may contraindicate supplementation; seek professional advice.
High‑dose preformed vitamin A can carry risks in pregnancy and for smokers; supplementation may be contraindicated during breastfeeding, in chronic fat‑malabsorption or with certain medications—consult a healthcare professional before use.