The spare tire many U.S. adults carry around their middles has been linked to a host of health risks, including, some research has found, decreased cognitive ability in men. The relationship between weight and dementia has been controversial, however, and some researchers have had difficulty finding a consistent association between these two health issues—especially in women.

Now, a new study has found that a woman's total body mass—as well as how she carries extra weight—affects her cognitive abilities after menopause.

As part of the Women's Health Initiative cohort study, 8,745 postmenopausal women ages 65 through 79 (who did not have dementia) were examined and completed questionnaires about lifestyle and other potential risk factors. Some 70 percent of the women had body mass indexes (BMIs) of 25 or more, making them overweight or obese. All of the women also completed standard cognitive tests known as the Modified Mini-Mental State Examination.

In general, women with higher BMIs fared more poorly on the cognitive tests, the researchers noted in the study, published online July 14 in Journal of the American Geriatrics Society.

"Obesity and a higher body mass index are not good for your cognition and your memory," lead study author Diana Kerwin, an assistant professor of medicine at Northwestern University, said in a prepared statement. "The added weight definitely had a detrimental effect." On average, with each up-tick in BMI, a woman's cognitive test score decreased by nearly a full point as well—even after adjusting for vascular disease risks and other demographic factors.

But overweight and obese women who carried more of their extra weight around their hips (rather than around their stomachs) tended to do worst on the cognitive tests.

Scientists are still uncertain about the mechanisms behind these correlations. "The fat may contribute to the formation of plaques associated with Alzheimer's disease or a restricted blood flow to the brain," Kerwin said. Studies like these might help researchers home in on differences in fat and individual physiologies that could influence cognitive performance. This work could lead to better dementia prevention.

In the meantime, the findings join a long list of reasons for women to strive for healthy BMIs—especially as obesity itself can lead to other ailments, including diabetes and hypertension, which have been linked to increased risk for dementia.

Image courtesy of iStockphoto/wlfella