Low concentrations of 25-hydroxyvitamin D and long-term prognosis of COPD: a prospective cohort study

Role and importance of vitamin D deficiency in long-term prognosis of chronic obstructive pulmonary disease (COPD) still remains undetermined. We tested the hypothesis that among individuals with COPD, those with low concentrations of 25-hydroxyvitamin D have a poorer prognosis compared to those with normal concentrations. We studied 35,153 individuals from the general population aged 20-100 years with 25-hydroxyvitamin D measurements and spirometry, the Copenhagen City Heart Study [median follow-up 21 years (range 13 days-36 years)] and the Copenhagen General Population Study [7.1 years (3 days-13 years)]. Spirometric COPD (n = 5178; 15% of all) was defined as forced expiratory volume in 1 s (FEV₁)/forced vital capacity (FVC) < 0.70 in individuals without asthma and clinical COPD (n = 2033; 6%) as FEV₁/FVC < 0.70 and FEV₁ < 80% of predicted in ever-smokers aged > 40 years without asthma and with cumulative tobacco consumption ≥ 10 pack-years. In spirometric COPD, median age at death in years was 70.2 (95% confidence interval [CI] 64.4-71.2) for individuals with 25-hydroxyvitamin D < 12.5 nmol/L and 80.3 (74.4-83.4) for those with ≥ 50 nmol/L. In clinical COPD, corresponding values were 69.0 (63.3-70.9) and 76.2 (73.8-78.0). In spirometric COPD, multivariable adjusted hazard ratios for individuals with 25-hydroxyvitamin D < 12.5 nmol/L versus those with ≥ 50 nmol/L were 1.35 (95% CI 1.09-1.67) for all-cause mortality, 1.63 (1.00-2.64) for respiratory mortality, 1.14 (0.76-1.70) for cardiovascular mortality, 1.37 (0.90-2.06) for cancer mortality, and 1.61 (1.04-2.49) for other mortality. In clinical COPD, corresponding values were 1.39 (1.07-1.82), 1.57 (0.91-2.72), 0.88 (0.51-1.53), 1.63 (0.99-2.67), and 2.00 (1.12-3.56). Low concentrations of 25-hydroxyvitamin D were associated with an increased risk of death in individuals with COPD. No clear pattern of association could be observed for cause of death; however, there may be an increased risk of respiratory, cancer, and other mortality. It is likely that low concentrations of 25-hydroxyvitamin D is a marker of poor health in COPD.