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).
RECOMMENDATIONS
No published guidelines discuss using vitamin D in managing asthma. An American Academy of Family Physicians (AAFP) summary of the Cochrane systematic review recommends that family physicians await further studies and updated guidelines before recommending vitamin D for patients with asthma.12 The AAFP also points out that the Endocrine Society has recommended vitamin D supplementation for adults (1500-2000 IU/d) and children (at least 1000 IU/d) at risk for deficiency.
Editor's takeaway
In the meta-analyses highlighted here, researchers evaluated asthma patients with a wide range of ages, baseline vitamin D levels, and vitamin D supplementation protocols. Although vitamin D reduced asthma exacerbations requiring steroids overall, the effect was driven by 3 studies of patients with low baseline vitamin D levels. As a result, disentangling who might benefit the most remains a challenge. The conservative course for now is to manage asthma according to current guidelines and supplement vitamin D in patients at risk for, or with known, deficiency.
