Smoking does not protect against dementia or Alzheimer's disease

April 20, 2000

Smoking and dementia in male British doctors: prospective study

Smoking does not protect against dementia or Alzheimer's disease, shows a study in this week's BMJ, contradicting the implications of some previous research.

Doll, Peto, and colleagues, from the Clinical Trial Service Unit and Epidemiological Studies Unit, Radcliffe Infirmary Oxford, report on observations of over 34,000 male UK doctors whose smoking habits have been reviewed every six to 12 years since 1951, to determine the impact on their health. They also reviewed the published data on the associations between smoking and Alzheimer's disease.

Over 24,000 of the doctors had died by the end of 1998. Dementia was mentioned on the death certificates of 483. Among 473 whose smoking habits were recorded at least 10 years before their death, when they would not have been influenced by the start of the disease, the prevalence of both Alzheimer's disease (the predominant cause) and of other dementias was similar in both smokers and non-smokers. If anything, persistent smoking may increase rather than decrease the age specific onset rate of dementia, conclude the authors.

The previous suggestions that smoking might be protective, say the authors, came from studies that were flawed because they were too small, or had relied on information about smoking habits from people other than the sufferers themselves.

Carol Brayne from the Institute of Public Health, Cambridge, writes in an accompanying editorial that a protective effect for nicotine is biologically plausible. This is because of the boosting effect of the drug on neurotransmitter systems in the brain, which are damaged in Alzheimer's disease, she says. But adds that these effects are likely to be short-lived. In the long term, smoking increases the risk of vascular dementia, because it increases the risk of vascular disease in general. "The public health message is clear: at the population level there is no protective effect of smoking in dementia."

(Paper) Professor Richard Doll, Clinical Trial Service Unit and Epidemiological Studies Unit, Radcliffe Infirmary, Oxford

Tel: +44 (0)1865 557 241
Fax: +44 (0)1865 558817/512439

(Editorial) Dr Carol Brayne, Department of Public Health and Primary Care, Institute of Public Health, Cambridge

Tel: +44 (0)1223 330 334
Fax: +44 (0)1223 330 330


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