Rising levels of obesity in middle age could cause a major rise in the number of dementia sufferers, researchers have warned.
The risk of having dementia almost doubles with midlife obesity, the UK Health Forum said.
Dr Laura Webber and Tim Marsh found that by 2050 almost 7% of the population over 65 are predicted to suffer from dementia, costing £41 billion a year compared with £23 billion at present.
They said: "This study adds to the existing body of evidence which shows the importance of policies and interventions to prevent obesity and its related diseases in the population, including dementia."
The study, presented at the European Congress on Obesity in Liverpool, also predicted that by 2050, nearly half of men and 31% of women will be obese.
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Dr Simon Ridley, head of research at Alzheimer's Research UK, said: "Research shows that obesity in midlife is a risk factor for dementia and these projections suggest that rising obesity in the UK could contribute to growing levels of dementia over the coming decades.
"Dementia already has an enormous impact on individuals, families and communities and it is concerning to see that this could become even greater than previously predicted.
"We know that age is the biggest risk factor for dementia, and while we can't change our age, research suggests that lifestyle choices during midlife could help to keep our brains healthy as we age."
Jessica Smith, research officer at the Alzheimer's Society, said we "can't afford to ignore" the risk of "piling on the pounds".
She said: "It's easy to see the immediate impact of piling on the pounds but we can't afford to ignore the long-term effects.
"Evidence shows that obesity increases the risk of developing dementia. This study highlights the impact obesity will have on the numbers of people with the condition in the future.
"The changes that cause dementia develop over many years, so maintaining a healthy weight and exercising regularly - especially in midlife - are hugely important in reducing your risk."