Vitamin D Supplementation in the Armed Forces

The study will comprise of an original investigation that will take the form of a prospective intervention (two matched groups) study. Condition-1 will be a vitamin D supplementation group (50.000 IU every two months), and Condition-2 will be a placebo supplementation group. The primary research aim of this project is to evaluate the effectiveness of vitamin D supplementation to reduce stress fracture risk and susceptibility to skin, soft tissue infection (SSTI) and respiratory infection in Royal Marine recruits undertaking arduous physical training in a randomised control trial (RCT). The secondary research aims are: 1. To investigate whether supplementation of vitamin D3 at a dose of 50.000 IU every two months (equivalent to 800 IU per day) is effective in reducing the risk of stress fracture and susceptibility to skin, soft tissue and respiratory infection. 2. To examine changes in vitamin D status (relative to baseline serum 25(OH)D concentration), serum PTH concentration, and markers of bone turnover in response to vitamin D3 supplementation during the winter and summer months. 3. To identify interactions between dietary intakes, physical fitness, physical characteristics (body mass, BMI, thigh girth), smoking habit, alcohol consumption, and stress fracture prevalence with serum 25(OH)D status, serum PTH concentration and markers of bone turnover in the vitamin D3 supplemented group vs. the placebo supplemented group.