Abstract
Vitamin D3 exhibits strong antioxidant properties. However, its effect on oxidative stress after strenuous endurance exercise remains unclear. Therefore, we investigated the effects of vitamin D3 supplementation on strenuous endurance-exercise-induced oxidative stress. In this study, 26 male participants consumed vitamin D3 (5,000 IUs of vitamin D3 daily for 4 weeks) or placebo. After four weeks, all participants performed strenuous endurance exercise at 65% of ˙VV˙<math><mover><mtext>V</mtext> <mo>˙</mo></mover> </math> O2max. Blood samples were collected before and after four weeks of supplementation to determine the participants' serum 25(OH)D concentration. Additionally, venous blood samples were collected before, immediately after, two hours after, and 24 hours after the strenuous endurance exercise test to analyze markers of oxidative damage (thiobarbituric acid reactive substances, and protein carbonylation) and antioxidant enzyme activity (catalase, glutathione peroxidase, and superoxide dismutase). After four weeks of vitamin D3 supplementation, the concentrations of protein carbonylation and superoxide dismutase at post-0-h, post-2-h, and post-24-h were significantly higher in the placebo group than in the vitamin D3 group (all p < 0.05); the concentration of thiobarbituric acid reactive substances was significantly higher in the placebo group than in the vitamin D3 group at post-24-h (p < 0.05); and the concentration of catalase was significantly higher in the placebo group than in the vitamin D3 group at post-0-h (p < 0.05). Our results indicated that four weeks of 5,000-IU vitamin D3 supplementation (oil form) effectively increased the participants' serum 25(OH)D concentration and mitigated the accumulation of strenuous-endurance-exercise-induced markers of oxidative stress (e.g., thiobarbituric acid reactive substances and protein carbonylation).