Weekly Vitamin D₃ supplementation improves aerobic performance in combat sport athletes

AbstractVitamin D₃ supplementation can affect the strength and power of an athlete, however the effect on endurance performance remains unclear. Twenty-seven recreational male combat athletes with at least 12 months experience within combat sports were recruited (age: 24 ± 4 years, stature: 176 ± 6 cm, weight: 77 ± 14 kg). Participants completed baseline testing for blood haemoglobin and haematocrit, upper and lower body VO_2peak and upper and lower body Wingate. Following testing participants were stratified to 50,000IU (D1), 80,000IU (D2) or 110,000IU (D3) of vitamin D₃ per week. They then completed a 6-week placebo period followed by a 6-week supplementation period. Retesting was carried out after the placebo and supplementation period. There was a significant effect for time for haemoglobin and haematocrit, upper and lower body VO_2peak and upper body Wingate power (P < 0.01) but no effect for dose of vitamin D given. Performance data were normalised to vitamin D intake and there was a moderate effect size between D1 and D2 for lower body VO_2peak (d = 0.6), upper body VO_2peak (d = 0.13) and upper body average power (d = 0.75), with a large effect size between D1 and D2 for haemoglobin (d = 1.19), haematocrit (d = 0.93) and upper body peak power (d = 0.95). There was a large effect size for D1 compared to D3 for all variables (d > 0.8). Therefore, there is no additional benefit to increasing dose above 50,000IU vitamin D per week. Given the endurance adaptations from vitamin D supplementation and the importance of endurance for combat performance, recreational combat athletes should supplement at 50,000IU per week for six weeks.