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Grasping for any way to prevent Alzheimer’s

Recent studies have suggested correlations between certain lifestyle-related risk factors and Alzheimer’s,but scientific proof is still elusive.

Written by New York Times | Published: August 7, 2011 12:23 am

PAM BELLUCK

Is there a way to prevent Alzheimer’s disease? Last month,a study presented at the Alzheimer’s Association International Conference in Paris suggested there might be,something that would give hope to millions who worry that one day they may be struggling with dementia.

The new study,by researchers at the University of California,San Francisco,estimated how many Alzheimer’s cases might be attributable to certain behaviours or conditions: physical inactivity,smoking,depression,low education,hypertension,obesity and diabetes.

The authors used a mathematical model to surmise that these behaviours and conditions,all of which can be modified,are responsible for about half of the roughly 5.3 million Alzheimer’s cases in the US and 34 million cases worldwide.

And they calculated that if people addressed these risks—by exercising,quitting smoking,increasing their education or losing weight,for example—a significant number of Alzheimer’s cases could be prevented. Reducing the prevalence of these risk factors by 10 per cent,the researchers estimated,could prevent 1.1 million cases worldwide; reducing these risk factors by 25 per cent could prevent more than 3 million cases.

The operative word was “could.” As the researchers pointed out,there is not yet scientific proof that any of these risk factors in fact cause Alzheimer’s. “These things are not definitive,” said one author,Dr Kristine Yaffe,a professor of psychiatry,neurology and epidemiology. “We’re assuming that these are sort of causally related to the risk of dementia and Alzheimer’s,but unless you have a great trial,you just don’t know.”

Indeed,research on prevention of Alzheimer’s is in its infancy. It has only been since the 1980s that dementia has not been considered a symptom of normal ageing. And studies on preventing Alzheimer’s can be complicated and costly,especially the randomised controlled trials that provide the strongest evidence. Such trials have to follow people for years,and isolating individual risk factors—separating obesity from hypertension,diabetes,nutrition and physical inactivity,for instance—is challenging.

Last year,a National Institutes of Health panel of experts with no vested interest in Alzheimer’s research concluded that “no evidence of even moderate scientific quality exists to support the association of any modifiable factor (such as nutritional supplements,herbal preparations,dietary factors,prescription or nonprescription drugs,social or economic factors,medical conditions,toxins or environmental exposures) with reduced risk of Alzheimer’s disease.” Most research,the panel found,involved observational studies,showing that people who did or did not get Alzheimer’s had certain characteristics beforehand,but not whether the characteristics were causal. The panel found the strongest evidence for only one conclusion: that the herb gingko biloba does not prevent Alzheimer’s.

Many members of the Alzheimer’s community were stung,considering the panel’s conclusions a “glass half empty,” said William Thies,the Alzheimer’s Association’s chief medical and scientific officer. “We would agree that we haven’t proven any of these risk factors,but there’s data that is pretty good for some of them. And in a world where we have lots of Alzheimer’s disease and no definitive medical intervention,prevention strategies that are based on lifestyle changes are certainly attractive.”

Yaffe and her colleague Deborah Barnes excluded risk factors like nutrition or brain exercise because they believed research was not solid enough. They used a more elastic threshold to evaluate research than the NIH panel because,Yaffe said,the panel “didn’t quite do the field justice.” Their model weighed the strength of existing research and how widespread the risk factors were. In the US,they estimated that 1.1 million Alzheimer’s cases,or 21 per cent,may be linked to physical inactivity. 15 per cent may owe to depression,11 per cent to smoking,8 per cent to midlife hypertension,7 per cent to obesity,7 per cent to low education and 3 per cent to diabetes.

Their estimates for the risk factors worldwide differed because some behaviours and conditions are more common than in the US. So low education accounted for 19 per cent,or 6.5 million cases,worldwide,while physical inactivity accounted for 13 per cent and obesity 2 per cent.

Dr John W. Williams Jr.,a professor of medicine at Duke University who led an analysis of Alzheimer’s prevention research for the NIH panel,said studies like Yaffe’s can be informative “when we don’t have other evidence” and can help shapers of public policy “make decisions about where to invest to reduce risk.” But he said: “What should individuals do with it? Probably not much.”

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