A bigger waistline and high body mass index (BMI) in the 60s may be linked to the signs of brain aging by at least a decade, says a study. 

"People with bigger waists and higher BMI were more likely to have thinning in the cortex area of the brain, which implies that obesity is associated with the reduced gray matter of the brain," said study author Tatjana Rundek. The study has been published in the journal 'Neurology.' "These associations were especially strong among those who were younger than 65, which adds weight to the theory that having poor health indicators in mid-life may increase the risk for brain aging and problems with memory and thinking skills in later life," said Dr Rundek, 

The study involved 1,289 people with an average age of 64. Two-thirds of the participants were Latino. Participants' BMI and waist circumference were measured at the beginning of the study. An average of six years later, participants had MRI brain scans to measure the thickness of the cortex area of the brain, overall brain volume, and other factors. A total of 346 of the participants had a BMI of less than 25, which is considered normal weight; 571 people had a BMI of 25 to 30, which is considered overweight; and 372 people had a BMI of 30 or higher, which is considered obese. 

For the waist circumference, which can be different for men and women, the normal weight group, which was 54 per cent women, had an average of 33 inches, the overweight group, which was 56 per cent women, had an average of 36 inches, and the obese group, which was 73 per cent women, had an average of 41 inches. Having a higher BMI was associated with having a thinner cortex, even after researchers adjusted for other factors that could affect the cortex, such as high blood pressure, alcohol use, and smoking. 

In overweight people, every unit increase in BMI was associated with a 0.098 millimeter (mm) thinner cortex and in obese people with a 0.207 mm thinner cortex. Having a thinner cortex has been tied to an increased risk of Alzheimer's disease. 
Having a bigger waist was also associated with a thinner cortex after adjusting for other factors. 

"In normal aging adults, the overall thinning rate of the cortical mantle is between 0.01 and 0.10 mm per decade, and our results would indicate that being overweight or obese may accelerate aging in the brain by at least a decade," Rundek said.  Rundek noted that the study does not prove that extra weight causes the cortex to get thinner. It only shows an association.  A limitation of the study was that, like many studies of older people, it is possible that the healthiest people are more likely to live longer and take part in studies, so that may affect the results.