Tibial bone responses to 6-month calcium and vitamin D supplementation in young male jockeys: A randomised controlled trial

Young male jockeys compromise bone health by engaging in caloric restriction and high volumes of physical activity during periods of musculoskeletal growth and development. The aim of this randomised, double-blinded, placebo-controlled trial was to establish whether calcium and vitamin D supplementation would improve bone properties of young male jockeys. We conducted a 6-month trial with two groups of weight-, height- and age-matched apprentice male jockeys (age=20.2±3.2yrs). Participants were supplemented with 800mg of calcium and 400IU of vitamin D (S, n=8) or a placebo (cellulose) (P, n=9) daily for 6-months. Baseline calcium intake was (669.7±274.3 (S) vs 790.4±423.9 (P) and vitamin D 64.6±19.5 (S) vs 81.2±24.4 (P) with no statistical differences. Peripheral quantitative computed tomography (pQCT) measured ultra-distal (4%) and proximal (66%) tibial bone properties at baseline and 6months. Blood-borne markers of bone turnover, P1NP and CTX and vitamin D concentration were assessed. After co-varying for height, weight and baseline bone measurements, the supplemented group displayed greater post-intervention bone properties at the 66% proximal site with cortical content (mgmm) 6.6% greater (p<0.001), cortical area (mm²) 5.9% larger (p<0.001), cortical density (mgcm²) 1.3% greater (p=0.001), and total area (mm²) 4% larger (p=0.003). No other between group differences in bone variables were observed. Blood analysis indicated higher vitamin D levels (18.1%, p=0.014) and lower CTx (ng/L) (-24.8%, p=0.011) in the supplemented group with no differences observed in P1NP. This is the first randomised controlled trial to examine the efficacy of calcium and vitamin D supplementation in improving bone properties in a highly vulnerable, young athletic, weight-restricted population. Results using pQCT indicate beneficial effects of supplementation on bone properties in as little as six months. Although the study size is small, this intervention appears promising as a strategy for improving bone health in young athletes in weight-restricted sports.