Abstract
Vitamin D deficiency has previously been linked to higher rates of exacerbation and reduced lung function in asthmatics. Previous randomised controlled trials investigating the effect of vitamin D supplementation have mainly focused on children with asthma. Trials involving adults have typically used bolus dosing regimens, and the main outcomes have been patient-focused without investigating underlying inflammation. The present study aimed to conduct a 12-week placebo-controlled randomised controlled trials administering a daily 5000 mu g (125 mu g) vitamin D-3 supplement to adults with mild to moderate asthma. A total of 32 participants were randomised to receive either the 5000 mu g vitamin D-3 supplement or an identical matching placebo. The primary outcome of the study was lung function measured by the ratio of FEV1:FVC (effect size 2<middle dot>5) with secondary outcomes including asthma symptoms and inflammatory biomarkers. There was a small but statistically significant higher increase in the mean (+/- sd) ratio of FEV1:FVC from baseline to post-intervention in the vitamin D group (+0<middle dot>05 +/- 0<middle dot>06) compared with the placebo group (+0<middle dot>006 +/- 0<middle dot>04, P = 0<middle dot>04). There was no effect of the intervention on asthma control test scores, or the inflammatory biomarkers measured. There was a moderate, significant association between baseline plasma 25(OH)D concentration and baseline plasma IL-10 (r = 0<middle dot>527, P = 0<middle dot>005) and TNF-alpha (r = -0<middle dot>498. P = 0<middle dot>008) concentrations. A daily vitamin D-3 supplement led to slightly improved lung function in adult asthmatics and may be a useful adjunct to existing asthma control strategies, particularly for individuals with suboptimal vitamin D status.