Vitamin D3 supplementation and upper respiratory tract infections in a randomized, controlled trial.

BACKGROUND: Randomized controlled trials testing the association between vitamin D status and upper respiratory tract infection (URTI) have given mixed results. During a multicenter, randomized controlled trial of colorectal adenoma chemoprevention, we tested whether 1000 IU/day vitamin D(3) supplementation reduced winter episodes and duration of URTI and its composite syndromes, influenza-like illness (ILI; fever and ≥2 of sore throat, cough, muscle ache, or headache) and colds (no fever, and ≥2 of runny nose, nasal congestion, sneezing, sore throat, cough, swollen or tender neck glands). METHODS: The 2259 trial participants were aged 45-75, in good health, had a history of colorectal adenoma, and had a serum 25-hydroxyvitamin D level ≥12 ng/mL. They were randomized to vitamin D(3) (1000 IU/day), calcium (1200 mg/day), both, or placebo. Of these, 759 participants completed daily symptom diaries. Secondary data included semiannual surveys of all participants. RESULTS: Among those who completed symptom diaries, supplementation did not significantly reduce winter episodes of URTI (rate ratio [RR], 0.93; 95% confidence interval [CI], .79-1.09) including colds (RR, 0.93; 95% CI, .78-1.10) or ILI (RR, 0.95; 95% CI, .62-1.46), nor did it reduce winter days of illness (RR, 1.13; 95% CI, .90-1.43). There was no significant benefit according to adherence, influenza vaccination, body mass index, or baseline vitamin D status. Semiannual surveys of all participants (N = 2228) identified no benefit of supplementation on ILI (odds ratio [OR], 1.14; 95% CI, .84-1.54) or colds (OR, 1.03; 95% CI, .87-1.23). CONCLUSIONS: Supplementation with 1000 IU/day vitamin D(3) did not significantly reduce the incidence or duration of URTI in adults with a baseline serum 25-hydroxyvitamin D level ≥12 ng/mL.