A third of Alzheimer's cases are potentially preventable if people improve their lifestyles, according to a new study.
Factors including a lack of exercise, smoking and a lack of education can all contribute to the disease, and reducing the risk from these could prevent some nine million cases by 2050, the research published in The Lancet Neurology today suggests.
The latest study, led by Professor Carol Brayne from the Cambridge Institute of Public Health at the University of Cambridge and funded by the National Institute for Health Research, lowers the estimate from previous research in 2011 which had suggested as many as one in two cases are preventable.
Smoking is one of the seven risk factors associated with Alzheimer's
The seven risk factors associated with Alzheimer's are diabetes, midlife hypertension, midlife obesity, physical inactivity, depression, smoking, and low educational attainment.
It is thought that by 2050 more than 106 million people will have Alzheimer's, up from 30 million sufferers in 2010.
Dr Deborah Barnes from the University of California, San Francisco and the San Francisco VA Medical Centre, who led the 2011 study and is a co-author on the new study, said the latest information could help to prevent and manage the disease in the future.
"It's important that we have as accurate an estimate of the projected prevalence of Alzheimer's as possible, as well as accurate estimates of the potential impact of lifestyle changes at a societal level," said Dr Barnes.
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Alzheimer's disease is placing an ever increasing burden on health services worldwide as well as on both patients and their carers.
"Our hope is that these estimates will help public health professionals and health policy makers design effective strategies to prevent and manage this disease."
While there is no one way to prevent dementia this research indicates ways to reduce the risks, Professor Brayne said.
"We know what many of these factors are, and that they are often linked," said Prof Bayne.
"Simply tackling physical inactivity, for example, will reduce levels of obesity, hypertension and diabetes, and prevent some people from developing dementia as well as allowing a healthier old age in general - it's a win-win situation."
In separate research presented at the Alzheimer's Association International Conference in Copenhagen at the weekend, results showed that regular eye tests could in future be used to diagnose early-stage Alzheimer's, while a reduced sense of smell could also be an early indicator of dementia.