July 14, 2010 -- Older women who are obese are more likely to experience memory problems, especially if their excess weight is located around their hips, a new study shows.
And researchers say the location of the fat seems to be important -- that it's worse for memory if it's around the hips than if it's located around women's waists.
Diana R. Kerwin, MD, an assistant professor of medicine and a physician at Northwestern Medicine at Northwestern University, examined data from the Women's Health Initiative hormone trials involving 8,745 cognitively normal, postmenopausal women ages 65 to 79.
Participants received an evaluation of brain function designed to detect cognitive and memory states, answered health and lifestyle questions, and submitted to measurements of height, weight, body circumference, and blood pressure.
Body mass index (BMI) is a statistical measure of a person's body -- calculated using weight and height. A BMI of 18.5 suggests a person is underweight, 18.5-24.9 is normal weight, 25-29.9 means the person is overweight, and 30 and higher is obese.
The researchers say their study shows that for every one-point increase in a woman's BMI, her memory score dropped by a point on a 100-point memory test called the Modified Mini-Mental Status Examination.
"The message is obesity and a higher Body Mass Index are not good for your cognition and your memory," Kerwin says in a news release. "While the women's scores were still in the normal range, the added weight definitely had a detrimental effect."
'Pear' Shaped vs. 'Apple' Shaped
Women who have excess weight around their hips are known as "pear" shapes, and those with extra weight around their waists "apple" shapes.
Kerwin says the reason pear-shaped women experience more memory loss and brain function deterioration than their apple-shaped counterparts is likely related to the type of fat deposited around the hips vs. the waist.
"Obesity is bad, but its effects are worse depending on where the fat is located," Kerwin says.
Cytokines -- hormones released by the predominant kind of fat in the body that can cause inflammation -- likely affect cognition, she says.
Scientists have already shown in previous research that different kinds of fat release different cytokines and have different effects on insulin resistance, lipids, and blood pressure.
"We need to find out if one kind of fat is more detrimental than the other and how it affects brain function," Kerwin says. "The fat may contribute to the formation of plaques associated with Alzheimer's disease or a restricted blood flow to the brain."
The findings should provide guidance to doctors treating or counseling overweight patients, the researchers say.
"The study tells us if we have a woman in our office and we know from her waist-to-hip ratio that she's carrying excess fat on her hips, we might be more aggressive with weight loss," Kerwin says. "We can't change where your fat is located, but having less of it is better."
Alzheimer's Disease: Men vs. Women
The researchers did not address whether their findings in the study on older women may be true for men. Alzheimer's disease, they write, is 1.5 times more likely to develop in women than men.
Previous research also has shown that obesity has been associated with poorer cognitive function in men. They also write that the discrepancy between men and women found in past studies may reflect differences in body weight and distribution of fat.
Kerwin tells WebMD in an email that the most important finding of the study is that "obesity is associated with worse cognitive function and that it has a more pronounced relationship if the woman" is pear-shaped.
"It is true, though, that fat distribution on the body, or the pear-shaped woman, which is a small waist and larger hips, and an apple-shape woman with a larger waist relative to hips and high waist-hip ratio, cannot be controlled and is the same throughout life, even if your weight changes," she says by email.
The study is published in the July 14 issue of the Journal of the American Geriatrics Society.
Kerwin discloses that she has received consultant fees from Pfizer Pharmaceuticals, Forest Laboratories, and Novartis Pharmaceuticals.