The purpose of this study is to examine the effect of vitamin D supplementation on vitamin D status, immunity and physical performance.

Vitamin D plays a key role in bone mineralisation and has been linked to immune defence maintenance and muscle function. Vitamin D is primarily obtained from endogenous synthesis in response to skin sunlight exposure and follows a seasonal pattern; whereby, vitamin D levels peak at the end of the summer and fall to a trough during winter. If winter vitamin D levels can be increased to match those found in summer using supplementation, it is proposed sufficient vitamin D levels will improve physical performance and reduce susceptibility to illness in military recruits.

Inclusion Criteria:

• Passed medical assessment by medical doctor

Exclusion Criteria:

• Medically deferred by medical doctor
• Regular sun bed use
• Holiday in a hot sunny climate in <3 months
• Regular vitamin D supplementation