Background: Cross-sectional studies suggest an association of 25-hydroxyvitamin D with exacerbations in patients with COPD, but longitudinal evidence from cohort studies is scarce. The aim of this study was to assess the association of serum 25-hydroxyvitamin D with exacerbations and mortality in primary care patients with COPD.
Methods: In the main analysis, we included 356 patients with COPD (GOLD [Global Initiative for Chronic Obstructive Lung Disease] stages II-IV, free from exacerbations for ≥ 4 weeks) from a prospective cohort study in Dutch and Swiss primary care settings. We used negative binomial and Cox regression to assess the association of 25-hydroxyvitamin D with (centrally adjudicated) exacerbations and mortality, respectively.
Results: Baseline mean ± SD serum 25-hydroxyvitamin D concentration was 15.5 ± 8.9 ng/dL, and 274 patients (77.0%) had 25-hydroxyvitamin D deficiency (< 20 ng/dL). Compared with patients with severe 25-hydroxyvitamin D deficiency (< 10 ng/dL, n = 106 [29.8%]), patients with moderately deficient (10-19.99 ng/dL, n = 168 [47.2%]) and insufficient (20-29.99 ng/dL, n = 58 [16.3%]) concentrations had the same risk for exacerbations (incidence rate ratio, 1.01 [95% CI, 0.77-1.57] vs 1.00 [95% CI, 0.62-1.61], respectively). In patients with desirable concentrations (> 30 ng/dL, n = 24 [6.7%]), the risk was lower, although not significantly (incidence rate ratio, 0.72 [95% CI, 0.37-1.42]). In patients taking vitamin D supplements, using different cutoffs for 25-hydroxyvitamin D or competing risk models did not materially change the results. We did not find a statistically significant association of 25-hydroxyvitamin D concentration with mortality.
Conclusions: This longitudinal study in a real-world COPD population that carefully minimized misclassification of exacerbations and the influence of confounding did not show an association of 25-hydroxyvitamin D with exacerbations and mortality.
Trial registration: ClinicalTrials.gov NCT00706602.