Oct. 25, 2010 -- People who are heavy smokers in their midlife years are more than doubling their risk of developing Alzheimer’s disease or other forms of dementia two decades later, a new study shows.
While smoking has long been known to increase the risk of dying from cancer and heart disease, researchers in Finland say they’ve found strong reason to believe that smoking more than two packs of cigarettes daily from age 50 to 60 increases risk of dementia later in life.
Scientists at the University of Eastern Finland and at Kuopio University Hospital, Finland, analyzed data from 21,123 members of a health care system who took part in a survey between 1978 and 1985, when they were between ages 50 and 60.
Diagnoses of dementia, Alzheimer’s disease, and vascular dementia were tracked from Jan. 1, 1994, when participants were 71.6 years old, on average, through July 31, 2008.
Among the key findings:
25.4% of the participants, or 5,367 people, were diagnosed with dementia an average of 23 years later.
Of patients with dementia, 1,136 were diagnosed with Alzheimer’s disease and 416 with vascular dementia.
Researchers say that people who smoked more than two packs of cigarettes a day in middle age had an elevated risk of dementia overall and also of each subtype, Alzheimer’s and vascular dementia, compared with nonsmokers.
On the other hand, former smokers or people who smoked less than half a pack per day did not appear to be at increased risk of developing dementia. And associations between dementia and smoking did not vary by race or sex.
Smoking is considered a well-established risk factor for stroke and may contribute to the risk of vascular dementia through similar mechanisms, the researchers say.
In addition, they say that smoking contributes to oxidative stress and inflammation, which are 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 researchers write.
Previously, a link between smoking and the risk of Alzheimer’s disease has been considered controversial, with some studies even suggesting that smoking reduces the risk of cognitive impairment, Parkinson’s disease, and other neurodegenerative conditions.
Although smoking’s ill effect on public health has been well established, the researcher say, this study shows its impact is likely to become even greater as the population ages and dementia prevalence increases.
The study shows heavy smoking was found to be associated with a greater than 100% increase in risk of dementia and its forms 20 years after midlife, and that the brain is thus “not immune to long-term consequences of heavy smoking.”