This is a feasibility double-blind randomised controlled trial in 32 participants. It evaluates the feasibility of a full trial which will examine the efficacy of weekly supplementation of cholecalciferol (vitamin D3) relative to placebo on the subsequent frequency and severity of objectively-verified symptomatic acute respiratory tract infection, overall and as a proportion of detected colonisations of the upper respiratory tract by 9 of the most common aetiologic viral pathogens.

The hypotheses of the full study are:

Primary The group treated with vitamin D3 will have a significantly lower frequency of symptomatic respiratory tract infections than controls.

Secondary

1. Among persons with detected viral colonisations of the nasopharynx, treated persons will have a lower frequency of symptomatic respiratory tract infection resultant than controls.
2. Treated group will have significantly less severe symptomatic RTIs than controls.
3. Treated group will have significantly shorter symptomatic RTI durations than controls.

For the pilot, a cohort of 32 healthy young adults satisfying inclusion criteria will be randomised to cholecalciferol supplement or identical placebo and evaluated daily for the occurrence of RTI symptoms and evaluated weekly for the presence of respiratory colonisation by relevant pathogens using nasopharyngeal swab and polymerase chain reaction using selected pathogen-specific primers. This pilot will demonstrate the logistic feasibility of the proposed study design and provide preliminary data which will inform a larger study to be undertaken next year.

Inclusion Criteria:

• Students undertaking study at the MS1 building of University of Tasmania Medical Sciences Precinct (17 Liverpool St Hobart TAS) for the full duration between May and September 2012

Exclusion Criteria:

• Persons who have used tobacco within the 6 months preceding study entry
• Persons who have used any vitamin D (cholecalciferol or ergocalciferol) supplements or calcium supplements within the 3 months preceding study entry and/or persons who refuse to not start taking any such supplement during the study
• Persons using any immunomodulatory medication, diuretic medication, antiepileptic medication, or barbiturates.
• Persons who presently have been diagnosed with any chronic infectious disease (e.g. HIV, tuberculosis), chronic immune deficiency or autoimmune condition, or respiratory condition (e.g. asthma, chronic obstructive pulmonary disease).
• Persons who are hypersensitive to vitamin D.