Does vitamin D supplementation reduce asthma exacerbations?

Abstract

Q: Does vitamin D supplementation reduce asthma exacerbations? Evidence-based answer: YES, to some extent it does, and primarily in patients with low vitamin D levels. Supplementation reduces asthma exacerbations requiring systemic steroids by 30% overall in adults and children with mild-to-moderate asthma (number needed to treat [NNT] = 7.7). The outcome is driven by the effect in patients with vitamin D levels < 25 nmol/L (NNT = 4.3), however; supplementation doesn't decrease exacerbations in patients with higher levels. Supplementation also reduces, by a smaller amount (NNT = 26.3), the odds of exacerbations requiring emergency department care or hospitalization (strength of recommendation [SOR]: A, meta-analysis of randomized controlled trials [RCTs]). In children, vitamin D supplementation may also reduce exacerbations and improve symptom scores (SOR: C, low-quality RCTs). Vitamin D doesn't improve forced expiratory volume in 1 second (FEV1) or standardized asthma control test scores. Also, it isn't associated with serious adverse effects (SOR: A, meta-analysis of RCTs).