Vitamin D supplementation offers no protection against acute respiratory infections

Taking vitamin D supplements does not appear to help reduce the risk of acute respiratory infections (ARIs) contrary to previous report, according to an updated meta-analysis.

Findings of a previous meta-analysis of 43 randomized controlled trials (RCTs) of vitamin D supplementation for prevention of ARIs showed evidence of a statistically significant protective effect (odds ratio [OR], 0.92, 95 percent confidence interval [CI], 0.86–0.99). [Lancet Diabetes Endocrinol 2021;9:276-292]

Researchers re-examined the link between vitamin D and ARI prevention by searching multiple online databases for relevant studies published between 2020 and 2024. They identified six new RCTs involving 19,337 participants. For the updated meta-analysis, data were pooled from three new RCTs and 43 that were identified previously, which involved 16,085 and 48,488 participants, respectively.

Using a random effects model, results showed that compared with placebo, vitamin D supplementation had no statistically significant effect on overall ARI risk (OR, 0.94, 95 percent CI, 0.88–1.00; p=0.057; 40 studies, n=61,589; I²=26.4 percent).

Prespecified subgroup analysis showed no evidence of effect modification by age, baseline vitamin D status, dosing frequency, or dose size.

In terms of safety, vitamin D was not associated with any serious adverse events (OR, 0.96, 95 percent CI, 0.90–1.04; 38 studies; I²=0.0 percent).

A funnel plot indicated left-sided asymmetry (p=0.0020 for Egger's test), suggesting the possibility that the previous overall finding of a protective effect of any vitamin D supplement was driven by small study effects.