Three in 10 cases of Alzheimer's disease could be prevented if people led healthier lifestyles, exercising more and not smoking, research suggests. And keeping to a normal weight and reducing blood pressure would also help slow the predicted sharp rise in numbers getting the disease.
The findings, published on Monday in the journal Lancet Neurology, suggest that such lifestyle changes could mean up to 200,000 fewer people in the UK having Alzheimer's by 2050.
The authors of the study, from Cambridge University, King's College London, and San Francisco, say that, in all, about a third of those destined to get Alzheimer's worldwide could avoid the disease via such health measures. Moves to tackle depression and low educational attainment, which also significantly increase risk of the disease, could help too.
Of the seven risk factors studied, lack of physical activity accounted for the largest proportion of cases of Alzheimer's in the UK, Europe and US, where studies have found that about one in three adults take so little exercise they are deemed inactive. The study also looks at three other risk factors: diabetes, high blood pressure and obesity.
Worldwide, low educational attainment was implicated in about 20% of all cases, though in the UK the percentage was half that. Smoking and depression were each considered to be linked to one in 10 cases everywhere, while diabetes, high blood pressure in middle age, and obesity in people in their 40s or 50s was estimated to account for between 2% and 8% of those The authors say the study results present a "more realistic" assessment of the proportion of potentially avoidable Alzheimer's cases. The figure of a third compares with the 50% previous estimate drawn up with the help of the same authors in 2011.
The latest calculation is based on the fact that many of the risk factors are closely related, whereas the previous study calculated the risk for each of these independently, yielding the higher figure.
The authors, led by Carol Brayne, a professor at Cambridge University's Institute of Public Health, said there was "consistent evidence" of an association between each of the seven risk factors and Alzheimer's disease. Reducing the relative risk of each of the factors by 10% could lead to 9m (8.5%) fewer cases by 2050, they said.
"Although there's no single way to prevent dementia we may be able to take steps to reduce our risk of developing [it] at an older age," said Brayne. "We know what many of these factors are, and that they are often linked. Simply tackling physical inactivity, for example, will reduce levels of obesity, hypertension and diabetes, and prevent some people from developing dementia."
Doug Brown, director of research and development at the Alzheimer's Society, recommended no smoking and switching to a Mediterranean diet.
He said: "This valuable study adds to a growing body of evidence strongly suggesting that simple lifestyle changes can help lower our risk of developing dementia. The prospect of preventing up to one in three cases of Alzheimer's disease is something we cannot ignore.
"We already know that what is good for your heart is good for your head, and there are simple things you can start doing now to reduce your risk of developing dementia. Regular exercise is a good place to start as well as avoiding smoking, and eating a Mediterranean diet."
Simon Ridley, head of research at Alzheimer's Research UK, said: "While age is the biggest risk factor for most cases of Alzheimer's, there are a number of lifestyle and general health factors that could increase or decrease a person's chances of developing the disease. This new analysis suggests that many cases of Alzheimer's could be prevented by increasing physical activity, decreasing blood pressure, quitting smoking and altering diet to reduce the cases of diabetes.
"There are over 820,000 people in the UK living with dementia and an ageing population will lead to spiralling numbers affected, so it is critical that we bolster our approaches to disease prevention.", Ridley added.
In separate research, published by Diabetes UK, experts found that fewer than one in four of the million people diagnosed with diabetes type 2 in the last four years had their condition "under control". The charity's chief executive, Barbara Young, said lack of such control raised the risk of kidney failure and amputations and reflected the fact that the NHS was offering just 14% of these patients vital education on their condition as soon as they were diagnosed.
