Heavy smoking in midlife may be
association with dementia in later years
Heavy smoking in middle age appears to be associated
with more than double the risk for Alzheimer's disease and other forms of dementia
two decades later, according to a report posted online now that will be published
in the February 28, 2011 print issue of Archives of Internal Medicine, one of
the JAMA/Archives journals.
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. Although smoking increases risks of most diseases
and of death, some studies have shown a reduced risk of Parkinson's disease and
other neurodegenerative conditions among smokers. "The link between smoking
and risk of Alzheimer's disease, the most common subtype of dementia, has been
somewhat controversial, with some studies suggesting that smoking reduces the
risk of cognitive impairment," the authors write.
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 (when participants were an average of
71.6 years old), through July 31, 2008.
A total of 5,367 participants (25.4 percent) 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 write.
"To our knowledge, this is the first study evaluating the amount of midlife
smoking on long-term risk of dementia and dementia subtypes in a large multiethnic
cohort," they conclude. "Our study suggests that heavy smoking in middle
age increases the risk of both Alzheimer's disease and vascular dementia for men
and women across different race groups. The large detrimental impact that smoking
already has on public health has the potential to become even greater as the population
worldwide ages and dementia prevalence increases."
This study was supported 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. This study was also supported by a Kaiser Permanente
Community Benefits Grant and National Institute of Health and Academy of Finland
Grant.
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