London (PTI): Want to save your brain? Watch your waistline. A new study has found that a big waistline in the 40s could almost triple the threat of dementia in old age.

Obesity is a known risk factor for Alzheimer's. But, according to the study by a team of international researchers, even those of normal weight are more at risk if they have a large waist.

"It is well known that being overweight in midlife and beyond increases risk factors for disease.

"However, where one carries the weight, especially in midlife, appears to be an important predictor for dementia risk," the British media quoted lead researcher Dr Rachel Whitmer as saying.

The researchers looked at 6,583 people aged between 40 and 45, measuring their abdominal fat levels with calipers. They then followed all of these people into their 70s to see who became ill, and who managed to maintain relatively good health.

The team found the 20 per cent of people with the largest waistlines had a 270 per cent greater risk of dementia than those with the smallest waists.