Compound or practice · Supplement
Vitamin A
Essential for vision and immunity; a public-health hero in deficiency, and a supplement to handle carefully — beta-carotene raised lung-cancer risk in smokers.
- Overall grade
- Grade B
- Last revised
- 2
- graded outcomes
- 1
- reference listed
A structured monograph in Prometheus's bundled library. Its grades are the monograph's own reading of the evidence, not a peer-reviewed review.
2 at grade A — 2 graded rows
What is known
Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.
- Deficiency / childhood mortalityEvidence grade A
In deficient populations
Largehigh
- Lung cancer (beta-carotene, smokers)Evidence grade A
Increased risk — ATBC/CARET
Moderatehigh
What is uncertain
Read off the same rows as above. Nothing here is added that the entry does not itself record.
- Caution with Vitamin D: Very high A can antagonize vitamin D's actions on bone.
- Watch with Vitamin D: Very high A can antagonize vitamin D's actions on bone.
Interactions
Documented pairings with supplements and medicines. A medicine on this list is a conversation for whoever prescribes it.
Vitamin DCaution
Very high A can antagonize vitamin D's actions on bone.
The evidence in words
What it is
Vitamin A covers preformed retinol (animal foods) and provitamin carotenoids like beta-carotene (plants) the body converts to retinol. It is essential for vision, epithelial integrity, immune function, and reproduction. Deficiency is a leading cause of preventable childhood blindness in low-income settings and a non-issue in well-fed populations.
How it works
Retinal is the light-sensing chromophore in the retina; retinoic acid is a hormone-like regulator of gene transcription governing cell differentiation and immunity. Preformed A is fat-soluble and stored in the liver, so it accumulates — the reason chronic high intake is toxic.
What the evidence shows
Grade A for correcting deficiency (childhood mortality and blindness in deficient populations). In replete adults, supplementation offers little, and the ATBC and CARET trials delivered a landmark warning: high-dose beta-carotene increased lung-cancer incidence in smokers. Preformed retinol is teratogenic in high doses during pregnancy. This is a nutrient to get from food, not to megadose.
How to use it
Food-first (liver, dairy, eggs, orange and dark-green vegetables). If supplementing, keep within the RDA range; pregnant women must avoid high preformed-retinol doses.
Safety & interactions
Chronic excess of preformed A causes liver damage, bone effects, and, in pregnancy, birth defects. Smokers should avoid beta-carotene supplements. Carotenoids from food are safe (at most, harmless skin yellowing). Vitamin D — Very high A can antagonize vitamin D's actions on bone.
Bottom line
A deficiency you fix, not a supplement you stack. Get it from food; avoid high-dose retinol in pregnancy and beta-carotene supplements if you smoke.
How it is used
As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.
- Food-first
- Liver, dairy, eggs, orange/green vegetables; supplement only within RDA.
Related reading
Entries that share this one's tags or conditions.
- Vitamin A for Deficiency / childhood mortalityEvidence grade A — In deficient populationsEvidence grade A
- Vitamin A for Lung cancer (beta-carotene, smokers)Evidence grade A — Increased risk — ATBC/CARETEvidence grade A
- Vitamin A: dosage and how to take itLiver, dairy, eggs, orange/green vegetables; supplement only within RDA.Evidence grade B
- Vitamin A: side effects, safety & interactionsChronic excess of preformed A causes liver damage, bone effects, and, in pregnancy, birth defects. Smokers should avoid Evidence grade B
Sources
As this entry records them: title, journal and year. None carries a DOI or PubMed id, so none is linked as a verified paper. Each link searches PubMed for the title; check that what you find is what the entry describes.
- 1.Effect of beta-carotene and vitamin A on lung cancer (CARET) — N Engl J Med, 1996. Search PubMed (opens in a new tab)
Last revised . A grade is this entry's reading of the evidence, not medical advice.