People who smoked two packs of cigarettes or more a day at midlife were more than twice as likely as nonsmokers to develop dementia and dementia subtypes such as Alzheimer’s disease, according to a report published online Oct. 25 in the Archives of Internal Medicine.
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Researchers found that people who smoked two or more packs of cigarettes a day at midlife were more than twice as likely to develop dementia than nonsmokers.
The association between midlife smoking and dementia 2-3 decades later remained robust after the data were adjusted to account for several confounding factors, including stroke. Therefore, smoking “seems to have some independent effect on vascular dementia, beyond acceleration of cerebrovascular disease,” said Dr. Minna Rusanen of the department of neurology at the University of Eastern Finland, Kuopio, and her associates.
Very few studies have addressed the long-term cerebrovascular consequences of smoking in middle age, and those that have done so had small sample sizes of predominantly white subjects, the investigators noted (Arch. Intern. Med. 2010 [doi:10.1001/archinternmed.2010.393]).
Dr. Rusanen and her colleagues studied the issue using data from a large, multiethnic cohort of more than 33,000 people who were members of the Kaiser Permanente Medical Care Program of Northern California. The study subjects took part in the Multiphasic Health Checkup and were first assessed at enrollment between 1978 and 1985, when they were aged 50-60 years. For the analysis, the medical records of 21,123 people who were still living and in the health plan at follow-up in 1994 were reviewed for dementia diagnoses.
A total of 5,367 people (25%) were diagnosed by neurologists, neuropsychologists, or internists as having dementia, including 1,136 cases of Alzheimer’s disease and 416 cases of vascular dementia.
After researchers adjusted for age, sex and certain cardiovascular risk factors, they found that people who smoked two or more packs per day at midlife were more than twice as likely as nonsmokers to develop dementia (risk-adjusted hazard ratio, 2.14), Alzheimer’s disease (HR, 2.57), or vascular dementia (HR, 2.72) 20-30 years later.
The association between smoking and dementia risk was analyzed separately for people who had stroke, compared with those who did not have stroke, because stroke is a robust predictor of dementia and is highly associated with smoking. Midlife smoking remained a robust independent predictor of dementia and dementia subtypes in that subanalysis, the investigators said. Compared with nonsmokers who had a stroke, those who had smoked two or more packs per day and had a stroke were 1.83 times more likely to develop dementia.
The link between midlife smoking and later dementia also remained robust when the data were adjusted for patient race, ethnicity, and gender. “Based on the present results, we can postulate that the deleterious effects of smoking on risk of dementia seem to be the same for both sexes and across different ethnic groups,” Dr. Rusanen and her associates said.
The study was supported by the National Graduate School of Clinical Investigation, Kuopio University Hospital, the Juho Vainio Foundation, the Maire Taponen Foundation, Kaiser Permanente Community Benefits, Finland’s National Institute for Health and Welfare, and the Academy of Finland. One of Dr. Rusanen’s associates reported ties to Elan Corp., Pfizer, Janssen, and Novartis.