Objective: To study the association between Alzheimer's disease and nicotine intake through smoking.
Design: Population based case-control study.
Setting: City of Rotterdam and four northern provinces of The Netherlands.
Subjects: 198 patients with early onset Alzheimer's disease, 198 controls matched for age and sex, and families of 17 patients in whom Alzheimer's disease was apparently inherited as an autosomal dominant disorder.
Main outcome measures: Age of onset of dementia, relative risk of Alzheimer's disease.
Results: 89 of 193 patients with Alzheimer's disease had a history of smoking compared with 102 of 195 controls. Among the patients and controls with a family history of dementia, smoking was significantly less common in those with dementia (40/95 with dementia v 55/96 controls; relative risk 0.35; 95% confidence interval 0.16 to 0.78). The risk of Alzheimer's disease decreased with increasing daily number of cigarettes smoked before onset of disease (relative risk 0.3 in those smoking greater than 21/day v 1 in non-smokers). In six families in which the disease was apparently inherited as an autosomal dominant disorder, the mean age of onset was 4.17 years later in smoking patients than in non-smoking patients from the same family (p = 0.03).
Conclusions: These findings suggest an inverse association between smoking and Alzheimer's disease, although smoking cannot be advocated for other health reasons. We speculate that nicotine may have a role in the aetiology of both Alzheimer's disease and Parkinson's disease.