It is now established that vitamin D deficiency (variously defined) is highly prevalent in patients with COPD.6–9 12 In line with these studies, we have shown in cross-sectional analysis that those with COPD were more likely to have vitamin D deficiency (<10 ng/mL) than those with normal lung function and the prevalence of vitamin D deficiency increased with increasing severity of COPD even after taking into account a wide range of possible confounders and mediators including smoking, physical inactivity, BMI and inflammation (IL-6). This evidence concerns the gene IL6 and vitamin D deficiency.