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


OBJECTIVE
We hypothesized that lower vitamin D levels will further enhance the association of COPD and its severity with total and CVD mortality.


METHODS
We 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.


RESULTS
From 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.


CONCLUSIONS
Lower 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.
Heart Disease Prevention Program, Division of Cardiology, School of Medicine, University of California, Irvine, California; Division of Pulmonary Medicine Diseases and Critical Care, Department of Medicine, School of Medicine, University of California, Irvine, California.
Hwa Mu
HM
Lee
Michael
M
Liu
Katherine
K
Lee
Yanting
Y
Luo
Nathan D
ND
Wong
D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D002318:Cardiovascular Diseases / Q000175:diagnosis / Q000401:mortality*; D002423:Cause of Death; D016009:Chi-Square Distribution; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D011379:Prognosis; D016016:Proportional Hazards Models; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis / Q000401:mortality* / Q000503:physiopathology; D012307:Risk Factors; D012720:Severity of Illness Index; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D014797:Vital Capacity; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000175:diagnosis / Q000401:mortality*
D015415:Biomarkers; D014807:Vitamin D; C104450:25-hydroxyvitamin D