Cigarette Smoking and Risk of Disabling Dementia in a Japanese Rural Community: A Nested Case-Control Study

BACKGROUND: Previous prospective cohort studies have examined the association between smoking and the risk of dementia, but the results were inconsistent. METHODS: A prospective, nested, case-control study was conducted to examine the association between cigarette smoking and risk of disabling dementia within the cohort of 6,343 men and women aged 35-85 years. Incident dementia was documented in 208 men and women (95 cases with and 113 cases without a history of stroke). Two control subjects per case were selected by matching for sex, age and year of examination. RESULTS: The multivariable odds ratios (95% CI) for current versus never smokers were 2.3 (1.1-4.7) for total dementia, 2.6 (0.8-8.2) for dementia with a history of stroke and 2.2 (0.8-5.7) for dementia without it, yielding no effect of stroke history on the smoking-dementia association. A dose-response relationship was noted between the years of cigarette smoking and the risk of total dementia, and a significant excess risk was found for smoking duration of >or=45 years. CONCLUSIONS: The present prospective study suggests that long-term cigarette smoking may raise the risk of disabling dementia.