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 [0.33,0.94]; 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.
Nearly 25% of US adults have below adequate vitamin C status (plasma concentrations <28 µmol/L), and 6% of the adult population is classified as deficient (<11 µmol/L). Poor vitamin C status is underdiagnosed as early indications are unremarkable (fatigue, malaise, depression). Such feelings may manifest as a reduced desire to be physically active; moreover, hypovitaminosis C may be associated with increased cold duration and severity. This double‐blind, placebo‐controlled, randomized study examined the impact of vitamin C (1000 mg daily) on physical activity (PA) and symptoms of upper respiratory tract infections in men during the peak of the cold season. Consenting adults (23.2±3.6 y; 25.1±3.9 kg/m2; 29.5±8.7 μmol/L) completed the Wisconsin Upper Respiratory Symptom Survey‐21 daily and the Godin Leisure‐Time Exercise Questionnaire weekly. PA was lower in controls (n=14) over the course of the 8‐week trial in comparison to the vitamin C group (n=15) (METs: +5.9±3.2 and +18.2±5.9 kcal· kg‐1· wk‐1; p=0.046). The overall cold symptom severity score was 4‐fold higher for controls versus the vitamin C group (2.4±0.7 and 0.6±0.1; p=0.010). The incidence of colds was also higher in controls as compared to the vitamin C group (2.2±0.7 and 0.3±0.1 colds; p=0.008). These data suggest measurable health advantages associated with moderate vitamin C supplementation in a population with adequate‐to‐low vitamin C status.
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