Abdominal obesity in middle age increases the risk of Alzheimer's and other forms of dementia in later life, according to a new study.
Researchers found that those with large stomachs in their 40s were significantly more likely to suffer mental decline by their 70s.
There is no clear reason for the association with the obesity - which could be just one part of a complex set of effects caused by unhealthy living that also impact on the brain.
Scientists studied 6,583 people, aged 40 to 45 years, in California and measured their levels of abdominal fat.
An average of 36 years later, 16% of the volunteers had been diagnosed with dementia.
Those who had the largest amount of waistline fat in their 40s were almost three times more likely to have developed dementia than those with the lowest amount.
Study leader Dr Rachel Whitmer, from the Kaiser Permanente Division of Research in Oakland, California, said: "Considering that 50% of adults in this country have abdominal obesity, this is a disturbing finding.
"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."