Heavy smoking in middle age is linked to more than double the risk for Alzheimer's disease and other forms of dementia two decades later, according to a new study.
Current estimates suggest smoking is responsible for several million deaths per year from causes such as heart disease and cancer, according to background information in the article.
Minna Rusanen, M.D., of University of Eastern Finland and Kuopio University Hospital, Kuopio, Finland, and colleagues analyzed data from 21,123 members of one health care system who participated in a survey between 1978 and 1985, when they were 50 to 60 years old.
Diagnoses of dementia, Alzheimer's disease and vascular dementia were tracked from Jan. 1, 1994 through July 31, 2008.
A total of 5,367 participants were diagnosed with dementia during an average of 23 years of follow-up, including 1,136 with Alzheimer's disease and 416 with vascular dementia.
Those who smoked more than two packs per day in middle age had an elevated risk of dementia overall and also of each subtype, Alzheimer's disease and vascular dementia, compared with non-smokers.
Former smokers, or those who smoked less than half a pack per day, did not appear to be at increased risk.
Associations between smoking and dementia did not vary by race or sex.
Smoking is a well-established risk factor for stroke, and may contribute to the risk of vascular dementia through similar mechanisms, the authors note.
In addition, smoking contributes to oxidative stress and inflammation, believed to be important in the development of Alzheimer's disease.
"It is possible that smoking affects the development of dementia via vascular and neurodegenerative pathways," the authors wrote.
The report will be published in the February 28 print issue of Archives of Internal Medicine, one of the JAMA/Archives journals.