Cigarette smoking and cognitive impairment: a 10-year cohort study in Taiwan.

The relationship between cigarette smoking and cognitive impairment is not a simple one. Some studies have demonstrated that cigarette smoking is a risk factor for cognitive impairment in the elderly, whereas other studies have shown cigarette smoking to be protective against dementia. This study aims to explore the relationship between cigarette smoking and cognitive impairment in elderly persons without dementia, during a 10-year period. Data were derived from a population-based cohort study of 1436 elderly Taiwanese. Cognitive function was measured by the SPMSQ both in 1993 and in 2003. A total of 1436 participants free of cognitive impairment at baseline (SPMSQ> or =6 in 1993) were included in these analyses. Subsequently, participants were divided into three groups: never, past, and current smokers. The effect of cigarette smoking on cognitive function was assessed using logistic regression. In the logistic regression model adjusted for age, education, hypertension, diabetes, heart disease, and stroke at baseline, persons who had quit smoking (Odds ratio=OR=0.31; 95% CI=0.18-0.53; p<0.001) and those who continued to smoke (OR=0.37; 95% CI=0.20-0.70; p<0.001) were about one-third as likely to develop cognitive impairment as were those who never smoked. However, no dose-response relationship was observed between pack-years and cognitive impairment. Past and current smokers were less likely to develop cognitive impairment during a 10-year follow-up than were those who had never smoked. The present study suggests that smoking may be protective for cognitive function.