OBJECTIVE: To conduct a clinical trial of high-dose versus low-dose vitamin D3 supplementation for ARI prevention in residents of sheltered-accommodation housing blocks ('schemes') and their carers in London, UK.

MEASUREMENTS AND METHODS: Fifty-four schemes (137 individual participants) were allocated to the active intervention (vitamin D3 2.4 mg once every 2 months +10 μg daily for residents, 3 mg once every 2 months for carers), and 54 schemes with 103 participants were allocated to control (placebo once every 2 months +vitamin D3 10 μg daily for residents, placebo once every 2 months for carers) for 1 year. Primary outcome was time to first ARI; secondary outcomes included time to first upper/lower respiratory infection (URI/LRI, analysed separately), and symptom duration.

MAIN RESULTS: Inadequate vitamin D status was common at baseline: 220/240 (92%) participants had serum 25(OH)D concentration <75 nmol/L. The active intervention did not influence time to first ARI (adjusted HR (aHR) 1.18, 95% CI 0.80 to 1.74, p=0.42). When URI and LRI were analysed separately, allocation to the active intervention was associated with increased risk of URI (aHR 1.48, 95% CI 1.02 to 2.16, p=0.039) and increased duration of URI symptoms (median 7.0 vs 5.0 days for active vs control, adjusted ratio of geometric means 1.34, 95% CI 1.09 to 1.65, p=0.005), but not with altered risk or duration of LRI.

CONCLUSIONS: Addition of intermittent bolus-dose vitamin D3 supplementation to a daily low-dose regimen did not influence risk of ARI in older adults and their carers, but was associated with increased risk and duration of URI.

METHODS: A total of 88 BC women were randomly assigned into one of four groups: i) omega-3 fatty acid (ω3) group; ii) vitamin D (VitD) group; iii) ω3+VitD group, and iv) the control. Participants were received either two 300 mg ω3 capsules daily, or one 50,000IU VitD tablet weekly, or both supplementation for 9-weeks. The QoL status was assessed by the European Organization for Research and Treatment of Cancer (EORTC) instruments of QLQ-C30 and QLQ-BR23 tools, while blood inflammatory markers of TNF-α hsCRP were used. All measurements were taken from baseline to the end of the intervention period. The detailed procedures of the present study were registered on ClinicalTrial.gov with the identifier NCT05331807.