SMOKING AND COGNITIVE IMPAIRMENT - A POPULATION-BASED STUDY

OBJECTIVE: To test the hypothesis that there is an inverse relationshi p between smoking and cognitive impairment by examining the prevalence and incidence of such impairment in a representative cohort of older urban residents. DESIGN: Survey follow-up with three interviews over a 4-year period. SETTING: City of Cleveland, Ohio. PARTICIPANTS: Six hu ndred forty-seven survivors of a population-based, multi-stage probabi lity sample of urban residents, aged 74 years and older in 1984. MEASU REMENTS: Past and present cigarette smoking was measured in 1984 by di rect questioning. Cognitive impairment was measured in 1984, 1987, and 1988 by the 10-item Short Portable Mental Status Questionnaire. Morta lity was determined at each interview date, and death certificates wer e obtained. Data were analyzed by univariate analysis, stratified anal ysis, and multivariate logistic regression. RESULTS: There were 99 cas es of cognitive impairment at baseline among 628 individuals for whom complete data were available. Crude data suggest that the prevalence o f cognitive impairment was lower among smokers than among non-smokers, but logistic regression, adjusted for age, income, and gender, showed this difference to be non-significant, OR 0.73; 95% CI (0.42, 1.29). Fifty-one new cases of cognitive impairment occurred during the 4-year observation period. Neither the crude data nor logistic regression sh owed any significant relationship between smoking and the incidence of cognitive impairment, OR 1.03; 95% CI (0.54, 1.99). Four-year mortali ty did not differ significantly between these older smokers and non-sm okers, but smokers died at a relatively younger age and were more like ly to die of diseases associated with smoking. CONCLUSION: This study does not confirm the hypothesis that there is a negative relationship between smoking and cognitive impairment. The mortality data suggest t hat case-control prevalence studies of the hypothesized relationship m ay be distorted by complex life-long trends in behavior, morbidity, an d mortality which could result in a misleading appearance of low preva lence of cognitive impairment among smokers. Additional large, prospec tive, population-based studies of the incidence of cognitive impairmen t and related disorders and possible protective or risk factors other than smoking are needed.