Associations Between Vitamin D and Tibial Density and Trabecular Microarchitecture in Army Infantry Recruits

Abstract

Serum 25-hydroxyvitamin D (25(OH)D) concentrations ≥50 nmol/L are advocated for optimal bone health. In military recruits, low 25(OH)D concentrations have been associated with increased stress fracture risk during initial training, but little is known of the effect of vitamin D status on bone density and microarchitecture in young healthy men. PURPOSE: To investigate the relationship between total serum 25(OH)D and bone density, structure and trabecular (Tb) microarchitecture of the distal tibia using high-resolution peripheral quantitative computed tomography (HR-pQCT) in young male British Army recruits. METHODS: 324 healthy British Army infantry recruits (age, 22 ± 3 years; height, 1.77 ± 0.06 m; body mass, 75.5 ± 10.2 kg) provided informed consent. In week one of training, scans were performed at the distal tibia of the non-dominant leg using HR-pQCT (Xtreme CT, Scanco Medical, Switzerland), and a blood sample was drawn for measurement of total serum 25(OH)D and intact parathyroid hormone (iPTH). Participants were enrolled onto the study across all seasons. Participants were stratified into two groups based on their total serum 25(OH)D concentrations: Sufficient (≥50 nmol/L) and Deficient (<50 nmol/L), and were also assessed with total serum 25(OH)D as a continuous variable. RESULTS: 39.5% of participants were classified Deficient (n = 128) and 60.5% as Sufficient (n = 196). There were no significant differences between groups in bone density, structure or Tb microarchitectural parameters (P>0.05). Cortical area (151 ± 28 vs 145 ± 26 mm2, P = 0.057, ES = 0.22) and sub-endocortical Tb density (301 ± 34 vs 294 ± 29 mg HA/mm3, P = 0.058, ES = 0.22) tended to be higher in the Sufficient than the Deficient group. Serum 25(OH)D was negatively associated with iPTH (r=-0.271; P<0.0001), and positively associated with cortical area (r=0.183; P<0.01), cortical thickness (r=0.147; P<0.0001), Tb density (r=0.127; P<0.05), and Tb volume to tissue volume ratio (r=0.128; P<0.05). CONCLUSION: Total serum 25(OH)D <50 nmol/L was not associated with impaired bone density or Tb microarchitecture of the distal tibia in young healthy men. These findings suggest that vitamin D status is not a key factor influencing bone strength. The role of vitamin D in stress fracture risk warrants further investigation. Supported by UK MoD (Army).