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Richard Doll Clinical Trial Service Unit and Epidemiological Studies
Unit, Radcliffe Infirmary, Oxford OX2 6HE
Correspondence to: R Doll
Objective:
To assess the possible association between smoking and dementia.
Design:
Prospective study.
Setting:
Cohort of British male doctors followed up since 1951.
Subjects:
34 439 male British doctors, with 24 133
deaths recorded.
Results:
For all types of dementia combined the
relative risk was 0.96 (95% confidence interval 0.78 to 1.18), based
on 473 deaths at a mean age of 81 years. For probable or definite Alzheimer's disease, the relative risk in continuing smokers was 0.99 (0.78 to 1.25), based on 370 deaths at a mean age of 82 years. In
aggregate, however, the other prospective studies indicate a direct,
although not clearly significant, association between smoking and the
onset of dementia in general and of Alzheimer's disease in particular.
Conclusions:
Contrary to previous suggestions
persistent smoking does not substantially reduce the age specific onset
rate of Alzheimer's disease or of dementia in general. If anything, it
might increase rather than decrease the rate, but any net effect on
severe dementia cannot be large in either direction.
© BMJ 2000
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