Substrate utilization and work efficiency during submaximal exercise in vitamin C depleted-repleted adults

A placebo-controlled, depletion-repletion protocol was utilized to examine the effect of Vitamin C status on substrate utilization during a 90 min wal k at 50% maximum oxygen consumption (VO2max). Nine vitamin C depleted subje cts (plasma vitamin C < 28 mu mol/L) agreed to participate in the 5-week st udy (aged, 27.6 +/- 2.5 years, mean +/- SE; 5 females, 4 males). Subjects w ere apparently healthy but unaware of their vitamin C status. Prior to the experimental period, VO2max was measured using open-circuit spirometry duri ng a graded walking protocol. Subjects ingested a placebo capsule daily dur ing weeks 1-3 and a 500 mg vitamin C capsule daily during weeks 4-5 of the experimental study. Mean plasma vitamin C rose nearly 3-fold and mean plasm a carnitine fell by nearly 20% at repletion (week 5) versus depletion (week 3). at end of week 3 and 5, subjects completed a 90 minute treadmill walk at an exercise intensity of 50% VO2max. The relative contribution of fat ut ilized for energy during walking did not differ in the vitamin C depleted v ersus repleted states. However, work performed by subjects and gross effici ency during exercise increased significantly at repletion versus depletion (10% and 15%, respectively). These data indicate that vitamin C depletion i s associated with reduced work efficiency during submaximum exercise.