Just in case you needed another reason to lose weight, a new study has found that midlife obesity may make brains age faster.

The study looked at weight, waist size, and markers of brain health, including cortical thickness, brain volume, and evidence of small strokes. It found that having a high body mass index (BMI) or large waist was associated with brains that appeared at least 10 years older than those of thinner people.

The research, which used data from the Northern Manhattan Study, a long-term study of Manhattan residents, and was led by the University of Miami Miller School of Medicine, could not say whether obesity actually causes the brain changes. It was published recently in Neurology, the journal of the American Academy of Neurology.

The study analyzed brain scans of 1,289 people with an average age of 64. Sixty percent were female and 66% were Latino. They were followed an average of six years after body measurements were taken. The heaviest group had a BMI of 30 or greater and a waist circumference of more than 40 inches for men and more than 35 inches for women.

Having a higher BMI or bigger waist was associated with having a thinner cortex or outer layer of the brain. The cortex is used for higher-level thinking and information processing. Thinning of this part of the brain is associated with a higher risk of Alzheimer’s disease. The link between BMI and cortical thinning was present even when the analysis adjusted for other factors known to affect the brain such as high blood pressure, alcohol use, and smoking, and it was strongest in study subjects who were younger than 65. In overweight people, the thinning got worse as weight climbed.

There was a weaker relationship between obesity and brain volume. The study did not find a significant relationship between obesity and small strokes.

The research is “consistent with the hypothesis that midlife exposure to poor cardiometabolic health increases risk for detrimental brain aging in late life,” the authors wrote.