Relationship of vitamin D status with lung function and exercise capacity in COPD

Background and objective The relationship between blood vitamin D level and clinical parameters in patients with chronic obstructive pulmonary disease ( COPD ) has been reported with conflicting results. We explored the effects of vitamin D on clinical characteristics of patients with COPD in K orea. Methods The study population comprised 193 patients with COPD from K orean O bstructive L ung D isease C ohort. The plasma level of 25‐ OH vitamin D 3 (25‐ OH ‐ VitD 3) was measured every year along with various clinical parameters such as lung function, 6‐min walking ( 6MW ) distance, quality of life, exacerbations and emphysema index. Generalized estimating equations and linear mixed model were used for statistical analysis. Results Of the 193 patients, 12 (6.2%), 28 (14.5%) and 153 (79.3%) were categorized into normal, insufficiency and deficiency groups. Clustered analysis showed that the plasma 25‐ OH ‐ VitD3 level was associated with the post‐bronchodilator ratio of force expiratory volume in 1 s/forced vital capacity ( FEV 1 / FVC ) (estimated = 0.001; P  = 0.022). The vitamin D deficiency group showed lower FEV 1 (estimated = −0.129, P  = 0.043), FEV 1 % predicted (estimated = −4.994, P  = 0.029) and FEV 1 / FVC ratio (estimated = −0.048, P  = 0.001) than did the non‐deficiency group. The 6MW distance tended to be shorter in deficiency group (estimated = −17.26, P  = 0.069) than in non‐deficiency group. Quality of life, exacerbation and emphysema index were not associated with plasma 25‐ OH ‐ VitD3 level. Conclusions We demonstrated a high prevalence of vitamin D deficiency in K orean patients with COPD and a significant relationship between vitamin D deficiency and airflow limitation. The exercise capacity tended to be decreased in the vitamin D deficiency group.