Daily vitamin D supplementation could be associated with a reduced risk of acute respiratory infections in children aged 1 to 15 years, although no overall protective effect was observed across all age groups, according to a recent review.

In a systematic review and meta-analysis, investigators evaluated randomized controlled trials (RCT) to determine the effect of vitamin D supplementation on the prevention of acute respiratory infections (ARI). This updated analysis built upon the investigators' 2021 analysis, which demonstrated a modest protective effect of vitamin D supplementation. Published in The Lancet Diabetes & Endocrinology, the current study incorporated six additional RCTs, including one involving 15,804 participants, and analyzed a total of 46 RCTs encompassing 64,086 participants.

Lead study author David A. Jolliffe, PhD, of the Blizard Institute in the Faculty of Medicine and Dentistry at Queen Mary University of London, and his colleagues applied a random-effects model to stratified aggregate data. The included RCTs were required to be double-blind, be ethically approved, and have prespecified ARI incidence as an outcome. The primary endpoint was the proportion of participants experiencing at least one ARI. Data were stratified by baseline serum 25-hydroxyvitamin D (25[OH]D) levels, age group, dosing frequency, and trial duration.

In the primary analysis of any vitamin D supplementation vs placebo, the pooled odds ratio (OR) for experiencing one or more ARIs was 0.94 across 40 studies including 61,589 participants. Subgroup analyses based on baseline 25(OH)D concentrations showed no statistically significant benefit, including among those with levels below 25 nmol/L. Age-based analyses also showed no benefit in infants younger than 1 year (OR = 0.95), adults aged 16 to 64 years (OR = 0.95), or adults aged 65 years and older (OR = 0.97), though a protective effect was observed in children aged 1 to 15 years (OR = 0.74).

Significant protective effects were found in trials using daily dosing (OR = 0.84), doses between 400 and 1,000 IU per day (OR = 0.70), and study durations of 12 months or less (OR = 0.85). No benefit was observed in trials that administered vitamin D weekly or monthly or in studies that lasted longer than 1 year.

Secondary outcomes, including upper and lower respiratory tract infections, antibiotic use, hospitalization, mortality, and adverse events did not differ significantly between intervention and control groups.

Although the point estimate was similar to that of the earlier analysis, the updated findings didn't demonstrate a statistically significant overall reduction in ARI risk with vitamin D supplementation. The investigators concluded that current evidence doesn't support the routine use of vitamin D solely for the prevention of acute respiratory infections.

Full disclosures can be found in the published review.