Vitamin A
One of the few vitamins where more is genuinely riskier, especially in pregnancy.
Vitamin A supports vision, immune function, and skin health, and it comes in two very different dietary forms: preformed retinol from animal foods and supplements, and beta-carotene from orange and dark-green vegetables, which the body converts to retinol as needed. That conversion step is exactly why beta-carotene is the safer route to high intakes: retinol accumulates in the liver and is genuinely teratogenic at high doses, which is why UK guidance sets a lower precautionary ceiling on preformed retinol for women of childbearing age, and why pregnant women are advised against high-dose retinol supplements specifically.
Reference values
Daily reference values from official nutrition authorities. These are population reference figures, not personal recommendations.
| Group | RDA | Upper limit | Source |
|---|---|---|---|
| General adult | 700 mcg | 1500 mcg | UK SACN DRVs -- pregnancy: RNI +100 mcg/day in last trimester (combined 700 mcg RAE). NHS/SACN advise against high-dose preformed retinol in pregnancy; UL 1500 mcg/day from supplements. Beta-carotene does not carry teratogen risk. |
| Women, 19+ | 600 mcg | 1500 mcg | UK SACN DRVs (1991) -- women 600 mcg RAE/day; UL set conservatively at 1500 mcg/day preformed retinol for women of childbearing age due to teratogen risk (SACN / NHS advice) |
| Men, 19+ | 700 mcg | 3000 mcg | UK SACN DRVs (1991) -- men 700 mcg RAE/day; EFSA UL 3000 mcg RAE/day total vitamin A (2006). SACN advises preformed retinol supplements not exceed 1500 mcg/day (teratogen risk) |
Forms and bioavailability
Not all forms are absorbed equally. The form on your supplement label affects how much your body can actually use.
| Form | Absorption | With food | Timing | Evidence |
|---|---|---|---|---|
| Retinyl palmitate (preformed) | Typical | With food | Morning | Strong |
| Retinol (preformed) | Typical | With food | Morning | Strong |
| Beta-carotene (pro-vitamin A) | Lower | With food | Morning | Likely |
How it pairs with other supplements
Works well with
Vitamins A and D share the RXR nuclear receptor heterodimerisation pathway and co-regulate gene expression. At normal supplement doses they are complementary. At high preformed retinol doses (>3000 mcg RAE/day) vitamin A may competitively impair vitamin D receptor signalling -- avoid very high retinol stacking with vitamin D.
Zinc is required for synthesis and release of retinol-binding protein (RBP) from the liver, which transports vitamin A to target tissues. Zinc deficiency impairs vitamin A status independent of liver stores.
Stack Almanac tracks whether your vitamin A is coming from retinol or beta-carotene, and flags a high retinol total for extra caution if you're a woman of childbearing age.
Track your Vitamin A in Stack Almanac
Last reviewed: 2026-07-08. Reference values are adult-general RDAs from UK. Individual needs may vary. This page is for informational purposes only and is not a substitute for professional medical advice.