Vitamin D supplementation to prevent asthma exacerbations: a systematic review and meta-analysis of individual participant data.

This was an individual participant data systematic review and meta-analysis of six randomized placebo-controlled trials in children and adults with asthma. Across the active intervention arms, 352 participants received vitamin D; studies were conducted in Poland, the United States, the United Kingdom, Japan, Ireland, and Canada.

Vitamin D supplementation was evaluated across six randomized placebo-controlled trials in people with asthma. Regimens varied by study and included oral vitamin D3 given daily or as intermittent bolus dosing, with doses ranging from 400 IU/day after a 100,000 IU bolus to 120,000 IU every 2 months, for durations from 15 weeks to 1 year.

Vitamin D supplementation reduced the rate of asthma exacerbations treated with systemic corticosteroids compared with placebo in the overall population, and the evidence was judged high quality. The apparent protective effect was strongest among participants with baseline 25(OH)D below 25 nmol/L, while no definitive effect modification was shown for age, sex, ethnicity, BMI, dosing regimen, inhaled corticosteroid use, or study duration. The intervention appeared safe, with no reported hypercalcaemia or renal stones and no overall increase in serious adverse events. The authors also noted that vitamin D supplementation could be cost-effective given the burden of asthma exacerbations.

The included trials were relatively small and heterogeneous in age group, dose, schedule, and duration, which limits certainty around subgroup effects. Several subgroup analyses were likely underpowered, and the packet does not provide per-arm outcome estimates or the pooled effect size for the primary endpoint.