Vitamin D inadequacy is a global health concern in athletes as well as the general population. Whilst the role of vitamin D in skeletal health is well defined, there remains uncertainty over whether vitamin D supplementation has an added benefit beyond bone health.
This randomised placebo-controlled trial in healthy male and female Gaelic footballers ( n = 42) investigated the effect of vitamin D 3 supplementation [3000 IU (75 µg) daily for 12 weeks, via an oral spray solution] on VO 2 max which was the primary outcome measure. Secondary outcomes included skeletal muscle and lung function.
Supplementation significantly increased total 25-hydroxyvitamin D concentrations compared to the placebo group (mean ± SD change from baseline, 36.31 ± 32.34 vs. 6.11 ± 23.93 nmol/L, respectively; P = 0.006). At baseline, 50 and 22 % of footballers presented with vitamin D insufficiency (31–49 nmol/L) and deficiency (<30 nmol/L), respectively. Total 25-hydroxyvitamin D concentration did not significantly correlate with any measure of physical performance. Analysis of covariance (ANCOVA) models demonstrated that vitamin D supplementation over 12 weeks had no significant effect on VO 2 max ( P = 0.375), vertical jump height ( P = 0.797), left and right handgrip strength ( P = 0.146 and P = 0.266, respectively), forced vital capacity ( P = 0.573) or forced expiratory volume at 1 s ( P = 0.665), after adjusting for confounders. The high prevalence of vitamin D inadequacy observed in this cohort of collegiate Gaelic footballers supports the need for vitamin D supplementation during wintertime to avoid being at risk of poor bone health.