Rising rates of obesity will lead to dramatic increases in the number of people with Alzheimer's disease, experts have predicted.
An unhealthy lifestyle increases a person's risk of Alzheimer's disease
In 50 years time, up to 2.5m people in the UK could have dementia unless steps are taken to stem the obesity epidemic, the Alzheimer's Society warned.
Better diet, more exercise and lower blood pressure would all help to reduce people's risk of the condition.
Around 700,000 people currently suffer from dementia in the UK.
The biggest risk factor for all types of dementia, of which Alzheimer's disease is the most common, is age.
Because people are living longer, the number of people with dementia is expected to increase to 1m in 20 years time and 1.5 million in 50 years time.
But experts are also starting to realise that lifestyle factors also have a big impact on a person's risk.
Obesity, smoking, high blood pressure and cholesterol all increase the risk of dementia because they can lead to damage of the blood vessels in the brain, which in turn leads to the death of brain cells.
Professor Clive Ballard director of research at the Alzheimer's Society said: "Obesity is a huge risk factor for Alzheimer's disease.
"People who are obese at 60 are twice as likely to develop dementia by the time they are 75.
"If we're not careful, it might be 2m or 2.5m people who have dementia in 50 years. This is a real opportunity to reduce the numbers."
He added that research had shown that regular exercise and a healthy diet could substantially reduce the risk.
And by delaying the onset of dementia by five years the frequency of the condition in the population could be halved.
The Alzheimer's Society has launched a "challenge dementia" website to help people find out more about how to reduce their chances of developing the condition.
Neil Hunt, chief executive of the Society, said dementia wrecked a person's ability to function and was very distressing for families.
HOW TO REDUCE YOUR RISK OF DEMENTIA
Eat less fatty food and salt and more fruit and vegetables
Lead an active social life
Ask your GP to check your blood pressure and cholesterol
"There are no cures but evidence is building that lifestyle choices do make a difference to your risk and we want to give people tips and advice on what they can do."
Professor Jeremy Pearson, associate medical director of the British Heart Foundation, said the same factors which increased a person's risk of heart disease increased the risk of dementia.
"There are very similar underlying pathologies for heart disease and dementia.
"There are things we can do to prevent dementia which we already know about."
Dr Tony Rudd, consultant stroke physician at Guys and St Thomas's Hospitals, said having a stroke was a significant risk factor for developing dementia and many of the risk factors that increase the risk of stroke are also risk factors for dementia.
"Public health initiatives to prevent stroke and related risk factors are essential if we are to reduce the number of people developing dementia."