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

In 250 men (21.4 ± 2.9 years; BMI 24.2 ± 3.0 kg∙m⁻²) commencing arduous military training during winter, we investigated the effect of 12 weeks 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 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 for vitamin D to affect the risk of lower body overuse musculoskeletal injury during 6 months of military training or subsequent 3 years of military service.