The early indications of vitamin C deficiency are unremarkable (fatigue, malaise, depression) and may manifest as a reduced desire to be physically active; moreover, hypovitaminosis C may be associated with increased cold duration and severity. This study examined the impact of vitamin C on physical activity and respiratory tract infections during the peak of the cold season. Healthy non-smoking adult men (18-35 years; BMI < 34 kg/m2; plasma vitamin C < 45 µmol/L) received either 1000 mg of vitamin C daily (n = 15) or placebo (n = 13) in a randomized, double-blind, eight-week trial. All participants completed the Wisconsin Upper Respiratory Symptom Survey-21 daily and the Godin Leisure-Time Exercise Questionnaire weekly. In the final two weeks of the trial, the physical activity score rose modestly for the vitamin C group vs. placebo after adjusting for baseline values: +39.6% (95% CI [-4.5,83.7]; p = 0.10). The number of participants reporting cold episodes was 7 and 11 for the vitamin C and placebo groups respectively during the eight-week trial (RR = 0.55; 95% CI 1; p = 0.04) and cold duration was reduced 59% in the vitamin C versus placebo groups (-3.2 days; 95% CI [-7.0,0.6]; p = 0.06). These data suggest measurable health advantages associated with vitamin C supplementation in a population with adequate-to-low vitamin C status.
NB, these were young men who had marginal vitamin C deficiency. However, physical activity levels were not really only “slightly increased”, since by week 7-8 of the trial, they were up by ~40%. Also noteworthy, the researchers state that about 22% of US adults have below adequate C status – and this assumes that that status is properly defined, which it may not be; i.e. lots more people could be vitamin C insufficient. Also, vitamin C blood concentrations were inversely and strongly related to BMI and fat mass.
Despite what the mainstream may tell you, it looks like vitamin C supplementation is far from useless, it may spare people from colds, and could also help weight loss by increasing physical activity.