Vitamin D insufficiency and elevated vitamin D metabolite ratios (VMR) are associated with increased risk of injuries: Results from the British Army Lower Limb Iinjury Pprevention (ALLIP) study

Introduction: British Army recruits suffer from musculoskeletal injuries (MSI) during initial training. Up to 10% suffer skeletal stress fracture (SFx) resulting in lost training days and medical attrition. There is evidence to suggest that vitamin D deficiency is prevalent in the army. Our aim was to determine vitamin D metabolites (VDM) in recruits upon starting training, and health outcomes after a 14-week training programme.

Methods: 940 of 2252 healthy army recruits, age 18–32 yrs were included in the analysis (ClinicalTrials.gov ID: NCT02416895). Excluded were those who took calcium/vitamin D supplements and with prior injuries. Serum 25OHD/24,25(OH)2D, 1,25(OH)2D and PTH were tested across all seasons. The co-primary endpoints were incidence of SFx, MSI, infections and days lost in rehabilitation (DLR) in relation to VDM.

Results: 38% of participants identified as vitamin D insufficient (25OHD<50 nmol/L) were associated with increased risk(OR): SFx(1.03), medial tibial stress syndrome (MTSS)(1.26), upper limb trauma (1.02), respiratory infections (1.13); and highly significant risk of upper limb overuse injuries(3.18) and subsequent DLR(3.49). 25OHD:24,25(OH)2D VMR was significantly increased at 25OHD<50 nmol/L (P<0.001). There was no significant relationship between 1,25(OH)2D and 25OHD, the distribution of 1,25(OH)2D:24,25(OH)2D VMR showed an exponential negative correlation with 25OHD (y=1525.8×−0.983, r2Exp =0.582, P<0.001). PTH was significantly higher (P>0.001) in subjects with high 1,25(OH)2D:24,25(OH)2D VMR and low 25OHD than those at the opposite. Cosinor-fit curves revealed circannual rhythm on all VDM and VMR except for 1,25(OH)2D. Baseline BMD was not associated with any health outcomes.

Conclusion: Vitamin D insufficiency is strongly associated with training-related injuries and lengthened rehabilitation. By using VMR models we demonstrated possible underlying mechanisms preceding the accelerated injury.