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 ≧45 years. Conclusions: The present prospective study suggests that long-term cigarette smoking may raise the risk of disabling dementia.