Chronic obstructive pulmonary disease (COPD) was associated with increased odds of having mild cognitive impairment (MCI) and memory loss in a cross-sectional, population-based study. The study, published in the November issue of the Mayo Clinic Proceedings, also showed a dose–response relationship with COPD duration and increasing risk for cognitive problems.
"In the absence of any effective therapy for dementia, the identification of risk factors for the development of MCI may hold the best promise for preventing or delaying the progression of early cognitive changes to clinical dementia," write Balwinder Singh, MD, from Mayo Clinic in Rochester, Minnesota, and colleagues.
"Recent studies suggest that up to 77% of patients with both COPD and hypoxemia have some form of cognitive impairment. However, few well-designed population-based studies have examined the association between COPD and MCI."
Therefore the researchers looked for an association between COPD and MCI and MCI subtype (amnestic or nonamnestic), in the population-based Mayo Clinic Study of Aging, using data from October 1, 2004, through July 31, 2007. Participants were aged 70 to 89 years and underwent a nurse assessment, neurological evaluation, and neuropsychological testing at study entry.
Using standardized criteria, a consensus panel diagnosed MCI, and the researchers reviewed medical records to identifyindividuals with COPD. Logistic regression models adjusted for potential covariates allowed evaluation of the associations of COPD and disease duration with MCI and its subtypes.
Of 1927 participants, 288 had COPD, which included 18% of men and 12% of women (P < .001). Prevalence of MCI was significantly higher in patients with COPD (27%) than in patients without COPD (15%; P < .001). The odds ratio (OR) for MCI was nearly double in those patients with COPD compared with those without COPD (OR, 1.87; 95% CI, 1.34 - 2.61). Findings were similar in both sexes.
In addition, COPD was associated with almost 2-fold higher odds of amnestic MCI (characterized by memory loss), but not with nonamnestic MCI. However, the study authors suggest that the nonsignificant association of COPD with nonamnestic MCI could be a result of reduced power on data stratification.
The associations of COPD with overall MCI and amnestic MCI were independent of age, sex, education, apolipoprotein E genotype, body mass index, depression, and a history of diabetes, hypertension, coronary artery disease, and stroke.
Dose–Response Effect for COPD Duration
There appeared to be a dose–response effect for COPD duration, with an OR for MCI of 1.60 (95% CI, 0.97 - 2.57) in patients with a COPD duration of 5 years or less and 2.10 (95% CI, 1.38 - 3.14) in patients with a COPD duration exceeding 5 years.
"This population-based study suggests that COPD is associated with increased odds of having MCI and its subtypes," the study authors write. "There was a dose-response relationship with the duration of COPD after controlling for the potential covariates."
Limitations of this study include its cross-sectional design, precluding causal inferences; reliance on physician diagnosis of COPD as recorded in medical records; and a primarily white population, which may limit its generalizability. The investigators recommend additional longitudinal studies in population-based cohorts to determine whether COPD is in fact associated with risk for incident MCI and dementia.
"COPD is reversible in early stages, especially in smokers," Dr. Singh said in a Mayo Clinic news release. "These findings are important because they highlight the importance of COPD as a potential risk factor for MCI and will hopefully lead to early intervention to prevent incidence or progression."
The National Institutes of Health (NIH), the Robert Wood Johnson Foundation, the Robert H. and Clarice Smith and Abigail van Buren Alzheimer’s Disease Research Program, the National Center for Advancing Translational Sciences from the NIH, and the Rochester Epidemiology Project funded this study. Some of the study authors reported various financial disclosures involving the National Institute on Aging, the Alzheimer Drug Discovery Foundation, the NIH, the Driskill Foundation, BI, Merck, Forrest, the Alzheimer’s Association, the National Advisory Council on Aging, Elan/Janssen AI, Pfizer Inc (Wyeth), GE Healthcare, Oxford University Press, and/or NIH/National Advisory Council on Aging.
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