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.