Vitamin C (moderate dose)

Tier 2 — promising · Immunity · Collagen · Antioxidant

Essential water-soluble antioxidant required for collagen synthesis, immune function, and non-haem iron absorption. The definitive 2013 Cochrane review (Hemila and Chalker, 29 trials, 11,306 participants, PMID 23440782) found regular supplementation reduces cold duration by 8% in adults and 14% in children, but does not prevent colds in the general population. A 2023 meta-analysis (Hemila and Chalker, 10 trials, PMID 38082300) found vitamin C reduces the severity of common colds by 15%. Intestinal absorption saturates at approximately 200 mg per dose; doses above 500 mg yield diminishing…

Dose: 200-500 mg/day for general health; split doses for better retention if taking 500 mg or more. Up to 1,000 mg/day is practical; beyond that, absorption is largely excreted. UL: 2,000 mg/day.