People who smoke heavily in middle age seem to more than double their risk of Alzheimer's disease and other forms of dementia late in life, research suggests.
Smoking is a well-established risk factor for stroke, but the link between smoking and risk of Alzheimer's and other types of dementia has been less clear since heavy smokers often die from other ailments before smoking's toll on the brain is evident.
To find out more, Dr. Minna Rusanen of the University of Eastern Finland in Kuopio and colleagues analyzed data from 21,123 people in California who participated in a survey between 1978 and 1985.
When the study began, the participants were between 50 and 60 years old, and they were tracked for an average of 23 years of followup.
During that time, 5,367 participants or 25 per cent were diagnosed with dementia, including 1,136 with Alzheimer's disease and 416 with vascular dementia, the researchers found.
Compared with non-smokers, those smoking more than two packs a day had 2.14 times higher risk of dementia 2.57 times higher risk of Alzheimer's, and 2.57 times higher risk of vascular dementia — another common and sometimes overlapping cause of progressive deterioration of memory and thinking.
"This study shows that the brain is not immune to the long-term consequences of heavy smoking," said the study's principal investigator, Rachel Whitmer, a research scientist with the Kaiser Permanente Division of Research in Oakland, Calif.
"We know smoking compromises the vascular system by affecting blood pressure and elevates blood clotting factors, and we know vascular health plays a role in risk of Alzheimer's disease," she added in a release.
Tobacco myth 'up in smoke'
"In conclusion, if, as a smoker, you are able to remain free of cancer and cardiovascular disease in middle age, you are also more likely to lose your memory and mental abilities in later years through increased likelihood of having Alzheimer's disease and vascular dementia," said Claude Messier of the school of psychology at the University of Ottawa, commenting on the research.
"Another health myth sponsored by the tobacco industry is going up in smoke," Messier added in an email.
Messier said strengths of the study include:
* The large number and variety of participants, which makes the sample representative of the population.
* The volunteers were evaluated in mid-life and followed over time, which is considered more accurate than asking people to recall what they did decades ago.
Limitations of the study include a less precise diagnosis of dementia, and self-reports of smoking that may be less reliable.
The researchers took into account factors such as age, sex, education, race, marital status, hypertension, body mass index, cardiovascular disease, diabetes and alcohol use.
One of the study's authors declared potential conflicts of interest from receiving honoraria from pharmaceutical companies.
The study was funded by the National Graduate School of Clinical Investigation, EVO grants from Kuopio University Hospital, and grants from the Juho Vainio Foundation and Maire Taponen Foundation.
The study was also supported by a Kaiser Permanente Community Benefits Grant and National Institute of Health and Academy of Finland Grant.
