Can vitamin D prevent acute respiratory infections?

This study found that low-dose daily or weekly vitamin D supplementation was protective against acute respiratory tract infections, but bolus dosing was not.

In 2-step analysis, patients benefited who: had baseline circulating 25-hydroxyvitamin D concentrations < 10 ng/mL (AOR = 0.30; 95% CI, 0.17-0.53; NNT = 4); had baseline circulating 25-hydroxyvitamin D levels of 10 to 28 ng/mL (AOR = 0.75; 95% CI, 0.60-0.95; NNT = 15); were ages 1.1 to 15.9 years (AOR = 0.59; 95% CI, 0.45-0.79); were ages 16 to 65 years (AOR = 0.79; 95% CI, 0.63-0.99); or had a body mass index < 25 (AOR = 0.82; 95% CI, 0.71-0.95).

Higher D levels are a different story. Vitamin D supplementation in people with circulating levels of 25-hydroxyvitamin D ≥ 30 ng/mL did not appear to provide benefit (AOR = 0.96; 95% CI, 0.78-1.18). Supplementation in this population did not influence any of the secondary outcomes, including risk for all-cause serious adverse events (AOR = 0.98; 95% CI, 0.80-1.20).

WHAT’S NEW

A more accurate snapshot

Previous studies of vitamin D and respiratory tract infections were mostly observational in nature. Those that were RCTs used variable doses of vitamin D, had variable baseline 25-hydroxyvitamin D levels, and employed various methods to monitor ARTI symptoms/incidence.^5-8 This is the first systematic review and meta-analysis of randomized, double-blind, placebo-controlled trials with supplementation using vitamin D₃ or vitamin D₂ that used individual participant-level data, which gives a more accurate estimate of outcomes when compared with traditional meta-analyses.

CAVEATS

Only the most deficient benefit?

Vitamin D supplementation was safe and protected against ARTIs overall, but the greatest effect of vitamin D supplementation on the prevention of ARTIs was noted in those who were most severely vitamin D deficient (those with circulating 25-hydroxyvitamin levels < 10 ng/mL, NNT = 4; 10-28 ng/mL, NNT = 15). There was no demonstrable effect once circulating 25-hydroxyvitamin D levels reached 30 ng/mL.

CHALLENGES TO IMPLEMENTATION

Breaking tradition

The study found that both daily and weekly doses of vitamin D were effective in reducing the incidence of ARTIs, but the doses used were much lower than the commonly used 10,000 to 50,000 IU bolus doses, which were ineffective in reducing ARTIs in the current meta-analysis. Since bolus dosing is an ingrained practice for many providers, changing this may prove challenging.

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