Supplements for immunity

Zinc 13–23 mg lozenges started within 24 h of cold symptoms shorten illness by ~33% (Hemilä Cochrane). Vitamin C 1 g daily reduces cold severity and duration by ~8% (Cochrane 2013) — meaningful for athletes/cold environments, modest for general public. Vitamin D3 if deficient reduces respiratory infection rates. Elderberry has positive but limited data for cold/flu. Avoid: high-dose immune-stimulating herbs (echinacea, andrographis, mushroom polysaccharides) if you are immunosuppressed — they may counteract therapy.