Vitamin D supplementation and musculoskeletal injury risk in young men undergoing arduous training: a randomised placebo-controlled trial.

In 250 men (21·4 (sd 2·9) years; BMI 24·2 (sd 3·0) kg·m-2) commencing arduous military training during winter, we investigated the effect of 12 weeks of vitamin D supplementation on lower body (pelvic girdle, sacrum, coccyx and lower limb) overuse musculoskeletal injury risk in a randomised, placebo-controlled trial. Participants received either simulated sunlight (1·3 × standard erythemal dose in T-shirt and shorts, three times per week for 4 weeks and then once per week for 8 weeks), oral vitamin D3 (1000 IU · d-1 for 4 weeks and then 400 IU · d-1 for 8 weeks) or placebo for each intervention. Serum vitamin D metabolites and bone metabolism biomarkers were measured at baseline, week 5 and week 12. At baseline, 29 % of participants were vitamin D sufficient (25-hydroxyvitamin D ≥ 50 nmol·L-1). Vitamin D supplementation achieved vitamin D sufficiency in 95 % of participants after 4 weeks. During 6 months of training and subsequent 3 years of military service, 100 lower body overuse musculoskeletal injuries were diagnosed by clinicians. Frailty models indicated no difference in injury risk between vitamin D and placebo during military training (HRplacebo:vitamin D = 1·23 (95 % CI 0·57, 2·66), P = 0·597) or military service (HRplacebo:vitamin D = 0·94 (95 % CI 0·60, 1·46), P = 0·782). Both safe simulated sunlight and oral vitamin D3 were effective in achieving and maintaining vitamin D sufficiency in almost all. There was no clear evidence that vitamin D affects the risk of lower body overuse musculoskeletal injury during 6 months of military training or subsequent 3 years of military service.