Leslie Silk

Date of Submission



Introduction: Young male jockeys compromise bone health by engaging in caloric restriction and high volumes of physical activity during periods of musculoskeletal growth and development. Failure to attain peak bone mass (PBM) during growth can have adverse short and long term musculoskeletal effects, with numerous studies demonstrating inferior bone health in jockey populations. However, no study to date has addressed counteracting the deleterious effects that participation in this sport has on bone health. The purpose of this six-month double-blind randomised placebo controlled trial was to examine the efficacy of 800mg calcium and 400 IU vitamin D daily supplementation on improving bone mineral properties at the tibia (weight-bearing) and radius (non-weight-bearing) using peripheral Quantitative Computed Tomography (pQCT) and blood-borne markers of bone turnover.

Three inter-related studies were designed following the findings of a systematic review and meta-analysis examining the effects of calcium and vitamin D supplementation on bone mineral density in healthy males. Study one examined the effect that the protocol had on markers of bone metabolism and bone properties of the radius. Study two was designed to investigate the impact of six months supplementation on weight-bearing bone while study three further explored alterations to radial and polar cortical bone properties at the tibial mid-shaft following the clinical trial.

Methods: Twenty-nine male jockeys (age=20.18 ± 3.23yrs) were originally recruited to the study with 17 completing the intervention. Bone properties at the ultra-distal (4%) and proximal (66%) radius and tibia using pQCT and serum vitamin D, Procollagen type 1 N propeptide (P1NP) and C-terminal telopeptide of type I collagen (CTx) were assessed at baseline and six months. Bone properties at the 66% tibial site were further analysed using BoneJ pQCT distribution plug-in. Polar and radial volumetric bone mineral density (vBMD) was measured in 36, ten degree cortical sectors (polar) and three concentric cortical divisions (radial). Polar distribution was further consolidated into four, 90 degree quadrants aligned to anatomical planes. Cortical mineral mass, endocortical and pericortical radii were also analysed.

Results: After co-varying for height, body mass and baseline bone measurements, the analysis of co-variance (ANCOVA) results of these combined studies demonstrate that six months calcium and vitamin D supplementation stimulated a reduction in bone resorption together with significant improvements to bone material properties at the proximal tibia in the supplemented group. ANCOVA serum analysis indicated significantly higher vitamin D levels (18.1%, p=0.014) and lower CTx (ng/L) (-24.8%, p=0.011) in the supplemented group with P1NP unchanged. The supplemented group displayed greater post-intervention bone properties at the 66% proximal site with cortical content (mg·mm) 6.6% greater (p<0.001), cortical area (mm2) 5.9% larger (p<0.001), cortical density (mg·cm3) 1.3% greater (p=0.001), and total area (mm2) 4% larger (p=0.003). No alterations were observed to bone material properties at the radius, nor the ultra-distal tibia or bone strength indices.

When cortical bone of the proximal tibia was examined in greater detail the supplemented group demonstrated greater endocortical vBMD in the posterior region of bone (1140.5 ± 6.3 vs 1116.2 ± 5.9; p=0.018) with a trend suggesting supplementation improved mineral mass and stimulated bone apposition in the posterior and lateral regions of the tibia.

Conclusion: 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 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.


School of Exercise Science

Document Type


Access Rights

Open Access


296 pages

Degree Name

Doctor of Philosophy (PhD)


Faculty of Health Sciences