Is there a way to prevent Alzheimers disease? Last month,a study presented at the Alzheimers 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 Alzheimers 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 Alzheimers cases in the US and 34 million cases worldwide.
And they calculated that if people addressed these risksby exercising,quitting smoking,increasing their education or losing weight,for examplea significant number of Alzheimers 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 Alzheimers. These things are not definitive, said one author,Dr Kristine Yaffe,a professor of psychiatry,neurology and epidemiology. Were assuming that these are sort of causally related to the risk of dementia and Alzheimers,but unless you have a great trial,you just dont know.
Indeed,research on prevention of Alzheimers 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 Alzheimers 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 factorsseparating obesity from hypertension,diabetes,nutrition and physical inactivity,for instanceis challenging.
Last year,a National Institutes of Health panel of experts with no vested interest in Alzheimers 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 Alzheimers disease. Most research,the panel found,involved observational studies,showing that people who did or did not get Alzheimers 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 Alzheimers.
Many members of the Alzheimers community were stung,considering the panels conclusions a glass half empty, said William Thies,the Alzheimers Associations chief medical and scientific officer. We would agree that we havent proven any of these risk factors,but theres data that is pretty good for some of them. And in a world where we have lots of Alzheimers 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 didnt 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 Alzheimers 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 Alzheimers prevention research for the NIH panel,said studies like Yaffes can be informative when we dont 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.