Substrate utilization and exercise efficiency in vitamin C depletion

Fatigue, a symptom of vitamin C (VC) deficiency, may be a result of decreased intramuscular carnitine, a metabolite essential for the transport of fatty acids into the mitochondria for energy utilization. We examined the effect of VC depletion(D)/repletion(R) on substrate utilization and exercise efficiency at 60 minutes of steady state exercise at 50% of VO₂ max. Nine VC depleted subjects were selected from a campus population (plasma VC <0.5mg/dL). Subjects avoided fruits and vegetables during the 5-week study. Placebo capsules were consumed daily during D, week 1-3. During R, week 4-5, 500mg VC was consumed daily. After R, plasma VC levels increased sig. (D=0.30 ±0.16mg/dL, R=0.87±0.20mg/dL, p<.001), and plasma free carnitine levels decreased sig. (D=9.36±2.41μg/ml, R=7.61 ±1.90μg/ml, p = .044). Heart rate and oxygen consumption remained constant between trials. Respiratory exchange ratio did not change; however, gross efficiency increased by 13%(p = .006), and work performed increased sig. (D=209.6±67.8kgm, R=236.1±80.1kgm, p = .021). Plasma urea/ creatinine ratio decreased sig. (D = 16.6±3.6, R = 13.7 ±2.6. p = .044) suggesting decreased protein utilization. We conclude that poor VC status was associated with reduced exercise efficiency.