Supplements
Vitamin C
Evidence ratingModerate
A water-soluble antioxidant vitamin. Meta-analyses report only a modest ~8% reduction in colds in the general population, but about a 50% lower post-exercise upper-respiratory infection risk in people doing intense endurance exercise such as marathons. It also acts as a coenzyme in collagen synthesis, aids iron absorption, and supports immune-cell function.
An ingredient with growing research
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Effects reported in research
Reduced post-exercise upper-respiratory infection risk reported in intense-endurance athletes (limited in the general population)
Acts as a coenzyme in collagen synthesis, supporting tendons, ligaments, and skin
Promotes absorption of non-heme iron
Dosage & timing
- Intake guidance is 100 mg/day.
- Studies commonly use 200–1,000 mg/day as a supplement, with plasma saturating around 200–500 mg.
- Above 1,000 mg, absorption drops and digestive symptoms such as diarrhea can occur.
Cautions
- •Intakes of 2,000 mg/day or more have been linked to a possible increase in kidney-stone risk.
- •People with kidney disease or iron overload, or on medication, should consult a doctor.
- •This site is for educational reference only.
Supporting research
Last checked: 2026-06-25