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Vitamin C
What Vitamin C 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 vitamin needed for collagen, cartilage and immune cells; also an antioxidant.
What the evidence supports
ODS: prevents and treats scurvy; for preventing colds the evidence is modest at best.
Dose and timing
RDA: men 90 mg, women 75 mg per day. UL 2000 mg. Any time; with food if your stomach is sensitive.
Cautions
High doses mostly end up in urine; diarrhoea is the usual dose limiter.
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 C fact sheet · checked 2026-09-03
Frequently asked questions
What does Vitamin C do?
A vitamin needed for collagen, cartilage and immune cells; also an antioxidant.
Does Vitamin C work?
ODS: prevents and treats scurvy; for preventing colds the evidence is modest at best.
How much vitamin c should I take?
RDA: men 90 mg, women 75 mg per day. UL 2000 mg. Any time; with food if your stomach is sensitive.
Is Vitamin C safe?
High doses mostly end up in urine; diarrhoea is the usual dose limiter. 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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