Vitamin D status is associated with bone mineral density and functional exercise capacity in patients with chronic obstructive pulmonary disease

Background. Chronic obstructive pulmonary disease (COPD) is associated with several extrapulmonary effects that contribute to the severity of the disease. Vitamin D is suggested to play a role in COPD and its related extrapulmonary effects. Aims. To determine the prevalence of vitamin D deficiency and its relation with bone density, muscle strength, and exercise capacity in patients with COPD. Methods. Our cross-sectional study included patients with moderate to very severe COPD. We collected data on lung function, body composition, bone density, quadriceps muscle strength, 6-minute walking distance, and plasma 25-hydroxyvitamin D (25(OH) D) concentration. Vitamin D deficiency was defined as plasma 25(OH) D concentration below 50 nmol/L. Results. In total, 151 COPD patients were included; 87 patients (58%) had vitamin D deficiency. Plasma 25(OH) D concentration was positively associated with bone density (P = 0.005) and 6-minute walking distance (P < 0.001) after adjustment for potential confounders. Plasma 25(OH) D concentration was not associated with quadriceps muscle strength. Conclusions. The majority of COPD patients had vitamin D deficiency. Plasma 25(OH) D concentration was positively associated with bone density and exercise capacity. Intervention studies are necessary to determine whether vitamin D supplementation is of benefit in the prevention or treatment of osteoporosis and poor exercise capacity in patients with COPD.