Does low vitamin D amplify the association of COPD with total and cardiovascular disease mortality?

backgroundChronic obstructive pulmonary disease (COPD) has been shown to be associated with lower levels of vitamin D, and the latter has been associated with total and cardiovascular disease (CVD) mortality. HYPOTHESIS: We hypothesized that lower vitamin D levels will further enhance the association of COPD and its severity with total and CVD mortality.

methodsWe studied 7746 US adults age ≥40 years without known CVD (mean age, 59.8 years) and followed up through 2006 (8.2 ± 2.5 years) for total and CVD mortality. Serum 25-hydroxyvitamin D levels were categorized as tertiles: first tertile, <50.9 nm/L; second tertile, 50.9 to 73.6 nm/L; and third tertile, >73.6 nm/L. Severity of COPD was classified on the basis of forced expiratory volume per second (FEV1 ): mild COPD (FEV1 ≥80%) and moderate or severe COPD (FEV1 <80%), and requires a FEV1 /forced vital capacity ratio <70%. With Cox regression, we examined the hazard ratio (HR) and 95% confidence interval (CI) for total and CVD mortality according to COPD/vitamin D category, using those with no COPD in the first tertile of vitamin D as the reference group.

resultsFrom Cox regression, unadjusted HRs increased successively with increasing COPD severity and decreasing vitamin D group to 4.5 (95% CI: 3.3-6.1) for total and 3.4 (95% CI: 2.2-5.3) for CVD mortality among those with moderate/severe COPD who were in the first tertile of vitamin D. After adjustment for age, sex, ethnicity, and other risk factors, these associations were attenuated but remained increased.

conclusionsLower levels of vitamin D may be associated with further increases in total and CVD mortality associated with COPD; however, age and cardiovascular risk factors appear to explain much of this association.