posted November 22, 2004 11:01 PM         

By John Fauber
Milwaukee Journal Sentinel

MILWAUKEE - Using brain scans after tracking weight gain in women over nearly a quarter century, researchers made a disturbing finding: As the body gets larger, the brain gets smaller.

The study and other reports appearing Tuesday in the journal Neurology are the latest in a growing amount of research suggesting that traditional heart disease risk factors such as obesity and diabetes can increase the odds that a person will develop dementia.

In one study, a Medical College of Wisconsin researcher and scientists in Sweden found that being overweight or obese throughout adulthood increased the risk of brain atrophy.

The researchers followed 290 Swedish women over a period of 24 years and did scans of their brains at the end of that period - when they were between the ages of 70 and 84.

Those who were overweight at various points throughout the study were significantly more likely to have a loss of brain tissue in the temporal lobe, a part of the brain involved in several cognitive functions, including language, comprehension and memory.

On average, the women with temporal lobe atrophy had a body mass index that was 1.1 to 1.5 points more than those who had no signs of atrophy. Body mass index is a measure relating a person's weight to their height. A BMI of 18.5 to 25 is considered normal weight; 26 to 29 is overweight; and 30 or more is obese.

The researchers found that for every one-point gain in BMI, the risk of temporal lobe atrophy increased 13 percent to 16 percent.

"This is the first study to show a higher BMI is related to brain atrophy," said lead author Deborah Gustafson, an assistant adjunct professor of family and community medicine at the Medical College who now works at Sahlgrenska University Hospital in Goteborg, Sweden.

There are several possible explanations for how being overweight contributes to brain cell loss. Excess fat likely contributes to a "vascular milieu" that is unhealthy for the brain, Gustafson said.

Overweight people are more likely to have high blood pressure, unhealthy cholesterol levels and diabetes, conditions that can contribute to blood vessel damage and blockages in the heart as well as the brain.

Beyond that, fat tissue is metabolically active, in that it increases levels of various hormones and other substances that can contribute to brain cell death, Gustafson said.

And the temporal lobe appears to be highly susceptible to blood vessel blockages and other vascular brain disease, she said.

Brain cell death in the temporal lobe appears to precede or accompany dementia, she said.

The study stands in contrast to an earlier finding that people with low BMI were more likely to have atrophy in the medial temporal lobe, said Jeffrey Kaye, director of the Layton Aging and Alzheimer's Disease Center at Oregon Health Sciences University.

"There is a range where being underweight is bad for your brain and being overweight is bad for your brain," said Kaye, a professor of neurology and biomedical engineering. "At the most general level, the brain likes a healthy body."

The study also bolsters the emerging concept that by improving traditional heart disease risk factors, a person also might reduce the risk of developing dementia, said William Thies, vice president for medical and scientific affairs with the Alzheimer's Association, which provided partial funding for the study.

"Body mass index is a driving force for so many of the other risk factors, such as high cholesterol, high blood pressure and adult onset diabetes," Thies said.

Thies said as much as 25 percent of dementias might be due to vascular risk factors.

In a separate study in Neurology, researchers with Mount Sinai School of Medicine in New York found another link between diabetes and dementia.

In a group of 1,852 Jewish men from Israel, those who had been diabetic were nearly three times as likely to develop dementia as non-diabetics.

Beyond that, diabetes in midlife was linked to the development of dementia nearly 30 years later.

The researchers said one possible explanation of the role of diabetes in dementia involves a substance in brain cells known as insulin-degrading enzyme. Diabetes might reduce levels of that enzyme, which, in turn, results in higher levels of amyloid-beta, a protein that many believe is a cause of Alzheimer's disease.

Thies, of the Alzheimer's Association, said the paper strengthens the belief that Alzheimer's disease actually begins 20 to 30 years before it is diagnosed.