Doubletake on Smoking to Prevent Dementia

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How does an activity that increases the risk of getting a particular disease become recommended as a preventative measure for that very same disease? That's what seems to have happened in the case of smoking and Alzheimer's disease.

"Smoking increases the risk of Alzheimer's disease by almost a factor of 2. So contrary to the widely held view that smoking actually protects people from Alzheimer's, it actually increases the risk of the disease," says Dr. Stanton Glantz, co-author of a study published in the Journal of Alzheimer's Disease.

Scientists have been researching connections between smoking and Alzheimer's disease for at least 20 years, yet dozens of studies appeared to come up with different results. The research team out of the University of California, San Francisco has a suggestion as to why that might be. "A lot of the classical studies were supported by the cigarette companies...We did a statistical analysis of all of the different studies done on Alzheimer's and found that the research funded by the tobacco industry tended to use inferior methods," Dr. Glantz said. "What we found was that [tobacco industry advisers] actually came up with a memo, that stated they were no longer going to use cohort studies, and it was because one of their paid consultants, P.N. Lee, looked into the situation and found that cohort studies were more likely to produce smoking as a risk factor."

An Alzheimer's association representative says the findings of this re-analysis of the research make sense. "My approach to it all is common sense, and I know common sense, as the saying goes, isn't all that common, but if we drink to excess it's going to be hard on our bodies, if we smoke it's going to be hard on our bodies," said Dr. Judy McKellar, Executive Director of the Alzheimer's Association in Oregon. "Science has proven that. So, thinking that smoking cigarettes will help our brain function better, seems to me, that it doesn't fall into the area of common sense, no matter what the prevalent attitude is."

Published:
Week of May 30 - June 6, 2010

Medical accuracy review by:
Dr. B. Ancelovic, MD, Geriatrician, Alzheimer's Weekly
Permalink:
http://www.AlzWeek.com/node/676

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http://iospress.metapress.com/content/l772t118k247u723/?p=e4a4daaf2b574ef6b82101ec55fcd97e&pi=7

Cataldo JK, Prochaska JJ, Glantz SA. Cigarette Smoking is a Risk Factor for Alzheimer's Disease: An Analysis Controlling for Tobacco Industry Affiliation. J Alz Disease 2010; 19(2):465-480

To examine the relationship between smoking and Alzheimer's disease (AD) after controlling for study design, quality, secular trend, and tobacco industry affiliation of the authors, electronic databases were searched; 43 individual studies met the inclusion criteria. For evidence of tobacco industry affiliation, http://legacy.library.ucsf.edu was searched. One fourth (11/43) of individual studies had tobacco-affiliated authors. Using random effects meta-analysis, 18 case control studies without tobacco industry affiliation yielded a non-significant pooled odds ratio of 0.91 (95% CI, 0.75–1.10), while 8 case control studies with tobacco industry affiliation yielded a significant pooled odds ratio of 0.86 (95% CI, 0.75–0.98) suggesting that smoking protects against AD. In contrast, 14 cohort studies without tobacco-industry affiliation yielded a significantly increased relative risk of AD of 1.45 (95% CI, 1.16–1.80) associated with smoking and the three cohort studies with tobacco industry affiliation yielded a non-significant pooled relative risk of 0.60 (95% CI 0.27–1.32). A multiple regression analysis showed that case-control studies tended to yield lower average risk estimates than cohort studies (by −0.27 ± 0.15, P=0.075), lower risk estimates for studies done by authors affiliated with the tobacco industry (by −0.37 ± 0.13, P=0.008), no effect of the quality of the journal in which the study was published (measured by impact factor, P=0.828), and increasing secular trend in risk estimates (0.031/year ± 0.013, P=0.02). The average risk of AD for cohort studies without tobacco industry affiliation of average quality published in 2007 was estimated to be 1.72 ± 0.19 (P< 0.0005). The available data indicate that smoking is a significant risk factor for AD.
Keywords
Alzheimer's disease, cigarette, cognition, cognitive impairment, smoking, tobacco