Clear evidence. Transparent sources. Practical guidance. Our evidence policyContact
Food Health Lab
Home › Supplements › Vitamin A

Vitamin A — The Complete Supplement Guide

Vital for vision and immunity — and one of the few vitamins that is genuinely toxic in excess. Forms, absorption, deficiency, and the pregnancy safety limit.

Reviewed by Bodil Isaksson, Licensed Biomedical Scientist (Sweden)Last reviewed July 2026Supplement guide

SupplementsVitaminsVitamin AFat-soluble

One of the few vitamins that is genuinely toxic in excess — because it is stored in the liver rather than flushed away, high-dose supplements can build up over time. For the short dietary version, see the Vitamins page.

Read first. Preformed vitamin A (retinol) is toxic in excess and causes birth defects — never take high-dose retinol in pregnancy. It is stored in the body, so daily high doses accumulate. Information, not a prescription.

Key takeaways

  • Get most vitamin A from food as beta-carotene; preformed retinol (animal foods/supplements) is the form that can build up to toxicity.
  • Adults need ≈ 650–900 µg RAE/day.
  • Don’t exceed 3,000 µg/day of preformed retinol — excess is toxic and especially risky in pregnancy.

Function

Vitamin A works through retinol and its active form retinoic acid:

  • Vision: forms rhodopsin in the retina — essential for night and low-light vision.
  • Immune defence: maintains the barrier linings and immune cells that fight infection.
  • Skin & epithelia: keeps skin and the linings of the eyes, gut and airways healthy.
  • Growth & reproduction: needed for normal cell growth, fertility and fetal development.
  • Gene expression: retinoic acid switches genes on and off, guiding cell differentiation.

Different forms — and which to choose

Preformed retinolRetinyl palmitate/acetate — the active animal form; potent and the type that can accumulate to toxicity.
Beta-carotenePlant provitamin the body converts to vitamin A as needed; food beta-carotene is non-toxic (but high-dose supplements carry a smoker cancer risk).
Topical retinoidsPrescription skin treatments (tretinoin etc.) — a related but separate medical use.

Absorption in the body

How muchFat-dependent; preformed retinol is well absorbed (~70–90%), while beta-carotene conversion is variable and less efficient. Excess is stored in the liver.
HelpsDietary fat in the meal; adequate zinc (needed to mobilise vitamin A).

Deficiency symptoms

SymptomsNight blindness first, progressing to dry eyes (xerophthalmia) and, untreated, blindness; weakened immunity and more infections; dry skin.
GlobalVitamin A deficiency is a leading cause of preventable childhood blindness worldwide.
Who's at riskFat-malabsorption (coeliac, pancreatic/liver disease) and very low-variety diets.

Recommended intake

Adults ≈ 650–900 µg RAE/day

Reference intakes (retinol activity equivalents):

  • Women: ~650–700 µg RAE/day · Men: ~750–900 µg RAE/day

Best sources: liver (very rich), egg yolk, dairy, oily fish (retinol); carrots, sweet potato, pumpkin, dark greens (beta-carotene).12

Therapeutic use

DeficiencyWHO high-dose vitamin A for children with measles or deficiency (supervised); correcting proven deficiency.
SkinPrescription oral/topical retinoids for severe acne and skin conditions — specialist-only.

Therapeutic doses

Only to correct deficiency (supervised)
EverydayA varied diet supplies enough; general supplements need only about the reference intake.
High doseTherapeutic high-dose retinol is a medical decision — never self-prescribed, and never in pregnancy.

Toxicity & upper limit

UL: 3,000 µg/day preformed retinol
Upper limit3,000 µg/day of preformed retinol for adults.1
Hypervitaminosis AHeadache, nausea, liver damage, bone thinning and hair loss with chronic excess.
PregnancyHigh-dose retinol is teratogenic (causes birth defects) — avoid retinol supplements and liver in pregnancy; beta-carotene from food is safe.

Bottom line: get vitamin A from food — colourful vegetables for beta-carotene, plus some animal foods. Only supplement retinol to correct a deficiency under guidance, keep well under 3,000 µg/day, and never high-dose retinol in pregnancy.

← All supplementsShort dietary version

References

Reference and upper-limit values are general adult figures from official bodies; individual needs vary. Therapeutic doses describe clinical/research use, not prescriptions.

  1. US NIH Office of Dietary Supplements. Vitamin A — Health Professional Fact Sheet (function, forms, intakes, food sources, deficiency, therapeutic uses, upper limit, interactions). ods.od.nih.gov
  2. EFSA. Dietary Reference Values & Tolerable Upper Intake Levels for vitamins (European reference intakes and ULs). efsa.europa.eu

This article summarizes nutrition science from official health authorities and peer-reviewed sources for education. It is not a substitute for individual medical advice, and the doses given are not prescriptions — always consult a professional before therapeutic supplement use, in pregnancy, or alongside medication.

✓
Bodil Isaksson, Licensed Biomedical Scientist (Sweden)

At Food Health Lab we explain what the science says in plain language, and we cite our sources so you can check for yourself.

Read next

Vitamin
Vitamin D
Vitamin
Vitamin E
Vitamin
Vitamin K