Background: Among individuals with vitamin D deficiency, daily vitamin D supplementation appears to lower risk of acute respiratory infection. However, recent trials, in different populations and using different regimens, have yielded null results. We investigated the effect of daily vitamin D supplementation (versus placebo) on risk of upper respiratory infection (URI) in older adults.
Methods: VITamin D and OmegA-3 TriaL (VITAL) is a randomized, double-blind, placebo-controlled trial of supplemental vitamin D and/or omega-3 fatty acids in generally healthy men (age ≥50 years) and women (age ≥55 years). This pre-specified analysis focuses on vitamin D3 (2000IU/day) versus placebo in the 15,804 (61%) participants with baseline serum total 25OHD level. The primary outcome was self-report of a recent URI at one-year follow-up.
Results: Participants had a mean age of 68 years and 51% were women; 76% were non-Hispanic White, 16% Black, and 8% other race/ethnicity. The mean (SD) 25OHD at baseline was 31 (10) ng/ml, with <12 ng/ml in 2.4%. The overall effect of vitamin D supplementation on recent URI was non-significant (OR 0.96; 95%CI, 0.86-1.06). In the pre-specified subgroup of primary interest (<12 ng/ml and denied taking concurrent vitamin D), which had only 255 participants, vitamin D supplementation was non-significant (OR 0.60, 95%CI 0.28-1.30). Statistical power to assess effect modification in other subgroups was limited.
Conclusions: In older adults not selected for vitamin D deficiency, supplemental vitamin D did not lower URI risk overall. Whether effects differ in subgroups requires further study.
Trial registration: ClinicalTrials.gov Identifier: NCT01169259.
Keywords: adults; nutritional supplement; randomized controlled trial; upper respiratory infection; vitamin D.
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