LAUSR

Observational studies link vitamin D deficiency with acute respiratory tract infection (ARTI) but results from randomised controlled trials are heterogeneous. We used data from The D-Health Trial (N = 21,315); ARTI was a pre-specified trial outcome. Participants were men and women aged 60 to 79 years (with volunteers aged up to 84 years), supplemented with monthly doses of 60,000 international units of vitamin D and followed for up to 5 years. Participants were asked to report occurrence of ARTI over the previous month via annual surveys, and a subset of participants completed 8-week respiratory symptom diaries in winter. We used regression models to estimate odds ratios, rate ratios and rate differences. Vitamin D supplementation did not reduce the risk of ARTI (survey OR 0.98, 95% CI 0.93 to 1.02; diary OR 0.98, 95% CI 0.83 to 1.15). Analyses of diary data showed that vitamin D reduced the average duration by 0.5 days (95% CI 0.2 to 0.7 days) and the average number of days with severe symptoms by 0.4 days (95% CI 0.3 to 0.6 days). Monthly bolus doses of 60,000 IU of vitamin D did not reduce the overall risk of ARTI but slightly reduce the duration of symptoms in the general population. The reduction in the duration of symptoms suggests a potential impact of vitamin D on the immune response to infection.