Up to one-third of the world's dementia cases could be prevented by addressing factors such as education, hypertension, diet, hearing loss and depression over the course of a person's lifetime, according to a new report presented Thursday at the Alzheimer's Association International Conference in London.

The report was compiled by the first Lancet Commission on Dementia Prevention and Care, which brought together 24 experts from around the world to review scores of studies and synthesize them into a model showing how lifestyle modification could reduce dementia risk.

Around 47 million people have dementia worldwide, and that number is projected to triple by 2050. The global cost of dementia in 2015 was estimated to be $818 billion, a figure also expected to rise with the number of cases.

The report identifies nine risk factors over a person's lifespan, including years of education before age 15; hypertension, hearing loss and obesity in middle age; and smoking, depression, physical inactivity, social isolation and diabetes in late life. The Lancet team considered each factor separately and also looked at how they related to one another to calculate how much modification of each could potentially affect a person's dementia risk.

In the past decade, research has increasingly pointed to controllable lifestyle factors as integral to reducing the risk of cognitive decline. Researchers believe that, as with heart disease, combating dementia is likely to require a multipronged, or "cocktail" approach combining drugs and lifestyle changes.

"The message is that conditions like dementia are not immutable and are substantially modifiable by the environment," said Lon Schneider, professor of psychiatry and the behavioral sciences at the Keck School of Medicine at the University of Southern California and a co-author of the Lancet report.

Noting that modifying all nine factors could reduce the risk by 35 percent, he said, "Compare that to how we're developing drugs to treat dementia. Dementia is not a condition that's ever going to be such that a single drug can be considered a cure for the illness." Lifestyle modification is inexpensive, he said, adding that a 35 percent reduction of risk is "far larger than anything you can ever expect for drugs."

Last month a report by the National Academies of Sciences, Engineering, and Medicine took a more cautious approach to the effects of lifestyle modification, finding that evidence of their efficacy derived from randomized controlled trials "remains relatively limited and has significant shortcomings."

That report, which was sponsored by the National Institute on Aging and used different methodologies than the Lancet Commission's, found that just three types of intervention offered "encouraging but inconclusive" evidence: cognitive training, blood pressure management for hypertension, and increased physical exercise.

Ronald C. Petersen, director of the Mayo Clinic Alzheimer's Disease Research Center and the Mayo Clinic Study of Aging, who presented that report Wednesday at the conference, said large trials that are currently ongoing or forthcoming could provide more evidence to support the effects of lifestyle intervention.

One such study was announced Wednesday at the conference: in 2018 the Alzheimer's Association plans to launch a $20 million two-year clinical trial to see if lifestyle changes can prevent cognitive decline.

Modeled after a larger 2014 study in Finland that showed positive results, the U.S. POINTER study will work with 2,500 older adults at risk for cognitive decline. It will test whether two years of intervention that includes physical exercise, nutritional counseling, social and cognitive stimulation, and improved self-management will help cognitive function in participants 60 to 79 years old.

Similar studies are also underway in Singapore and Australia.

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