Effects of vitamin D _<b>3</b> supplementation on cardiac, muscle, and immune responses after a marathon race: a single-blind, placebo-controlled trial

BACKGROUND: Strenuous endurance exercise imposes substantial physiological stress on the cardiovascular system and has been associated with transient elevations in cardiac biomarkers. Vitamin D₃ has been suggested to influence oxidative stress and immune responses. In this study, we investigated the effects of vitamin D₃ supplementation on biomarkers of cardiac, muscle, and immune responses following a marathon race. METHODS: Twenty-one amateur runners were allocated to either a vitamin D₃ supplementation group (receiving vitamin D₃ for 8 weeks) or a placebo group. All participants completed an official full marathon (42.195 km). Blood biomarkers were measured from 24 h before to 24 h after the race. RESULTS: Post-race increases in markers of muscle damage and cardiac stress were observed. Vitamin D₃ supplementation was associated with attenuated elevations in selected biomarkers demonstrating significant interaction effects. Compared with the placebo group, the vitamin D₃ group demonstrated attenuation of protein carbonyls (PC), the only oxidative stress marker showing a significant Group × Time interaction. No significant interaction effects were observed for thiobarbituric acid reactive substances (TBARS) or antioxidant enzymes. Both groups showed post-race increases in white blood cell counts, particularly neutrophils, whereas lymphocyte counts significantly decreased at 0.5 h and 2 h post-race. Immunoprofiling revealed time-dependent alterations in selected immune cell subsets, although no significant interaction effects were detected. Descriptive differences in recovery patterns were observed between groups, and exploratory correlation analyses suggested time-specific associations between immune cell subsets and biochemical markers during recovery. CONCLUSION: Vitamin D₃ supplementation may attenuate PC responses and was associated with lower creatine kinase (CK) and creatine kinase-MB (CK-MB) levels at 24 h post-race following marathon running. Immune alterations were time-dependent, with descriptive differences in recovery patterns between groups.