Middle-aged people's chances of developing dementia later in life have been calculated for the first time in a new study that outlines key lifestyle changes needed to reduce the risk.
By assessing factors such as blood pressure, body fat and cholesterol levels in 1,400 middle-aged Finns in the 1970s and 1980s, scientists were able to predict, with a 70% accuracy rate, the onset of dementia 20 years later.
The study, by the Ageing Research Centre in Stockholm, Sweden, has been hailed as a breakthrough that will prompt people to make the lifestyle changes needed to protect themselves from the condition.
It found that those who were obese, had high blood pressure or high cholesterol levels at 40 were more likely to develop dementia by the age of 60.
Having any one of these risk factors doubles a person's chance of developing dementia, while having all three increases their chances by six times, the study's lead author, Miia Kivipelto, said in an article in Lancet Neurology today.
"We have known for years that trying to control obesity, blood pressure and cholesterol can prevent heart disease," she said, "but now it's not only the heart you can save, but also the brain."
Speaking to BBC Radio 4's Today programme, she added: "We wanted to develop a kind of practical tool to predict the risk of dementia later in life and we found there were indeed several modifiable risk factors."
The study developed a "score card" to predict the likelihood of an individual developing dementia in old age.
It found that individuals with a low score on the risk factors have a 1% chance of suffering dementia in the next 20 years, while those with high scores face a probability as high as 16%.
The factors identified are the same as those linked to cardiac disease, but few people are aware that they can reduce the danger of dementia as well as that of heart problems by changing their lifestyle.
Alistair Burns, professor of old age psychiatry at the University of Manchester, said the findings were "extremely important".
"It opens the prospect for the prevention of dementia," he told Today.
"The emphasis that dementia is something that there is a possibility we can prevent is extremely important."
Dr Jose Bertolote, coordinator of and brain disorders at the World Health Organization, described the study as a "landmark paper".
But he cautioned that dementia also had genetic and age-related causes that could not be modified.
"Even if you remove all of the risk factors, and control your blood pressure and cholesterol, and are not obese, there is no guarantee that you will not develop dementia," he said.
Dr Kivipelto said: "If we can just delay the onset of dementia, that will have a major impact on public health.
"Opinions about dementia in the past have tended to be quite fatalistic, [but] this study shows that there is something you can do: the key risk factors are all modifiable lifestyle changes."
