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Vitamin A
What Vitamin A is, what the NIH ODS fact sheet says the evidence supports, typical doses, timing, and the cautions that come with it.
Supplements are not medicines and this page is not medical advice. Doses that help one person can harm another — with medicines, kidney or liver conditions, pregnancy, or before surgery, talk to a clinician before starting anything. More is not better.
What it is
A fat-soluble vitamin for vision, immune function and cell growth; as retinol and as beta-carotene precursors.
What the evidence supports
ODS: treats and prevents deficiency; supplements are not needed by most people eating a normal diet.
Dose and timing
RDA: men 900 mcg RAE, women 700 mcg RAE per day. With a fat-containing meal.
Cautions
Retinol accumulates — do not exceed the UL (3000 mcg RAE) and avoid liver-heavy diets while supplementing.
Interactions are the hidden risk: supplements can change how medicines work and vice versa. Give your clinician the full list before anything else.
Source: NIH Office of Dietary Supplements — Vitamin A fact sheet · checked 2026-09-03
Frequently asked questions
What does Vitamin A do?
A fat-soluble vitamin for vision, immune function and cell growth; as retinol and as beta-carotene precursors.
Does Vitamin A work?
ODS: treats and prevents deficiency; supplements are not needed by most people eating a normal diet.
How much vitamin a should I take?
RDA: men 900 mcg RAE, women 700 mcg RAE per day. With a fat-containing meal.
Is Vitamin A safe?
Retinol accumulates — do not exceed the UL (3000 mcg RAE) and avoid liver-heavy diets while supplementing. And the standing rule: tell your clinician everything you take — supplements interact with medicines.
Creatine
Studied doses: 3-5 g per day; loading protocols use about 20 g/day in 4 doses for 5-7 days.
Magnesium
RDA: men 400-420 mg, women 310-320 mg per day.
Vitamin D
RDA: 600 IU (15 mcg) to age 70, then 800 IU (20 mcg). UL 4000 IU.
Omega-3s (EPA/DHA)
No RDA for EPA/DHA; ALA: men 1.6 g, women 1.1 g per day. Many products supply 250-500 mg combined EPA+DHA per day.
Melatonin
Studied doses commonly 0.5-5 mg, taken 30-60 minutes before bed.
Iron
RDA: men 8 mg, women 19-50 18 mg, pregnancy 27 mg per day.
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