identify environmental and genetic factors associated with risk of vitamin D deficiency (25[OH]D concentration < 50 nmol/L). Results Mean serum 25(OH)D concentration was 45.4 nmol/L (SD 25.3); 171/278 (61.5%) participants were deficient. The following factors independently associated with increased risk of vitamin D deficiency: BMI >30 kg/m 2 (OR 1.87, p = 0.04) and blood draw during winter and spring seasons (OR 3.00, p < 0.01; OR 2.50, p < 0.01, respectively). The following factors

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... ly associated with reduced risk of deficiency: consumption of a vitamin D supplement, 100-400 IU/day (OR 0.42, p < 0.01); and a sunny holiday abroad no more than 2 months prior to blood draw (OR 0.27, p = 0.02). None of the 37 SNP investigated independently associated with vitamin D deficiency. Conclusions Vitamin D deficiency was highly prevalent among COPD patients in this study. Obesity and winter and spring sampling were risk factors for deficiency. Recent travel to a sunny country and consumption of vitamin D supplements were protective. Genetic variants in the vitamin D pathway that have previously been shown to associate with risk of vitamin D deficiency in healthy adult populations were not associated with deficiency in this patient group.