London: An expanding waistline along with other middle-age vices such as smoking and drinking not just harm your heart, they could also cause your brain to shrink, a new study has claimed.
Conditions such as diabetes and high blood pressure also take their toll on the grey matter, having an effect on brainpower just ten years later, the researchers found.
Doctors could use the information to pick out patients at a higher risk of dementia and encourage them to improve their lifestyles while there was still time, they said.
"Identifying these risk factors early could be useful in screening people for dementia and encouraging people to make changes to their lifestyle before it’s too late," study author Charles DeCarli, from the University of California at Davis said.
For their study, published in the journal Neurology, the researchers measured weight and height of more than 1,300 men and women in their 50s and 60s.
Their blood pressure, cholesterol and diabetes were also examined. Scans to measure brain volume were carried out over the next ten years and mental tests were also run on participants.
The brain shrinks with age, even in the healthiest of people. But in those with diabetes, the hippocampus – the brain's "memory hub" - shrank more quickly than in those without the condition, the researchers found.
The hippocampus also shrivelled faster in smokers. And those with high blood pressure were more prone to small lesions or areas of brain damage, known as "white matter hyper-intensities", they said. High blood pressure was also linked to a more rapid worsening of scores on mental tests, effectively ageing the brain by up to eight years, the researchers said.
Those who were obese in their 50s tended to fare poorly on the mental tests in the study.
A previous study of American pensioners found that obesity ages the brain by up to 16 years. It is thought that high levels of fat raise the odds of the arteries clogging up, cutting the flow of blood and oxygen.
It is estimated that half of cases of Alzheimer's could be prevented by lifestyle changes, such as doing more exercise, eating healthily and not smoking.
People who are overweight at 60 are more than twice as likely to get dementia by 75.