Vitamin C (megadose)

Tier 2 — promising · Prevention / Immunity

Cochrane found high-dose vitamin C does not prevent colds in the general public, though it may shorten them by about 8%. Your body absorbs about 200 to 400 mg at a time, so doses above that are mostly excreted. Athletes exercising in extreme conditions may get a 50% cold reduction benefit. Doses above 1 to 2 g per day increase kidney stone risk, especially in people prone to oxalate stones.

Dose: 200–500 mg/day is optimal; absorption maxes out around 400 mg per dose; doses above 2 g/day increase kidney stone risk