Is smoking associated with the risk of developing Alzheimer's disease? Results from three Canadian data sets

PURPOSE: To determine whether smoking is associated with Alzheimer's diseas e (AD). METHODS: Analyses were conducted using three Canadian data sets: the Univer sity of Western Ontario Dementia Study (200 cases, 163 controls), the Canad ian Study of Health and Aging (258 cases, 258 controls), and the patient da tabase from the Clinic for Alzheimer Disease and Related Disorders at the V ancouver Hospital and Health Sciences Centre (566 cases, 277 controls). The association between smoking and AD was investigated using bivariate analys es and multiple logistic regression models adjusted for the potential confo unders age, sex, educational revel, family history of dementia, head injury , and hypertension. RESULTS: The results of bivariate analyses were inconsistent across the thr ee data sets, with smoking status a significant protective factor, a signif icant risk factor, or not associated with AD. The results of multiple logis tic regression models, however, were consistent: any association between sm oking status and AD disappeared in all three data sets after adjustment for confounders. CONCLUSIONS: Smoking status was consistently not associated with AD across all three data sets after adjustment for confounders. Failure to adjust for relevant confounders may explain inconsistent reports of the influence of smoking on AD. Any protective effect of smoking may be limited to specific AD subtypes (e.g., early onset AD). Ann Epidemiol 2000;10:409-416. (C) 2000 Elsevier Science Inc. All rights reserved.