Vitamin C supplementation slightly improves physical activity levels and reduces cold incidence in men with marginal vitamin C status: a randomized controlled trial.  Schumacher SS 2014 [66]  AdultsRCT  Vitamin C (1 g/day for 8 weeks)  Reduced cold episodes in young men with low to average vitamin C status (p = 0.04). Cold duration was reduced 59% in the vitamin C vs. placebo groups (p = 0.06).