MONDAY, Nov. 22, 2004 (HealthDayNews) -- Obesity is harmful to the brain for women, but it doesn't appear to raise the risk of dying for men who have suffered heart attacks, according to two new studies.
Swedish researchers say that women who have been obese throughout their lives are more likely to lose brain tissue in the temporal lobe compared with women of normal weight. Loss of brain tissue has been linked to cognitive decline and an increased risk for Alzheimer's disease.
Obesity is a well-known risk factor for heart disease, but a separate study surprised researchers by finding that it didn't increase the risk of death in men who had already suffered a heart attack.
The Swedish paper "is the first study to show [that] a higher body mass index is related to brain atrophy," said lead researcher Deborah Gustafson, a psychiatrist at Sahlgrenska University Hospital in Göteborg.
The only significant relationship between body mass index (BMI) and brain atrophy was found in the temporal lobe, Gustafson said. "The temporal lobe is important for a number of reasons, including hearing, speech, language, comprehension, naming, memory, and visual processing of, for example, faces," she said.
BMI is a height-to-weight ratio to determine whether someone is of healthy weight; a BMI of 25 -- a 5-foot, 7-inch person weighing 160 pounds -- or above is considered to be overweight, while a BMI of 30 -- a person of the same height weighing 190 pounds -- or higher is deemed to be obese. Increased BMI accounted for about 8 percent of all dementia, Gustafson added.
In their study, Gustafson and her colleagues collected data on 290 Swedish women born between 1908 and 1922. Each woman had four exams between 1968 and 1992. At the last exam, they underwent a CT scan to determine if they had lost any brain tissue during the 24 years of follow-up, according to the report in the Nov. 23 issue of Neurology.
The researchers found that a higher BMI was directly linked to loss of brain tissue. "BMI was related to 11 to 14 percent higher odds of temporal lobe atrophy per one unit of [increased] BMI," Gustafson said. "Women who were, on average, heavier were more likely to have temporal lobe atrophy."
However, the amount of atrophy was not related to increasing levels of BMI, Gustafson said. "In other words, those women with more severe temporal lobe atrophy did not have a higher BMI compared to women with mild atrophy," she explained.
Gustafson speculated that the connection between BMI and loss of brain tissue may be due to fat causing more oxidative stress, resulting in an increase of free radicals in the body. Another reason may be because fat leads to atherosclerosis, which can limit oxygen flow to the brain. Still another possibility may be that fat causes the release of hormones and growth factors that are harmful to brain tissue, causing brain atrophy.
According to Gustafson, it is not known whether these results apply to men, or if the effect can be modified by losing weight.
"However, maintaining a healthy body weight over the course of one's life may decrease the odds of temporal lobe atrophy and subsequent dementia," Gustafson said.
"This finding fits logically with a previous paper that showed that BMI correlates with Alzheimer's disease," said William Thies, vice president for medical and scientific affairs at the Alzheimer's Association. "People with high BMI at middle age have more Alzheimer's disease."
Moreover, these findings support the need for more public education in how to maintain a healthy brain, Thies added. "Our Maintain Your Brain program tries to get people to understand that relatively simple interventions can make a profound difference in some of the risk factors that contribute to public health," he said.
For the heart attack-obesity study, researchers collected data on 5,010 middle-aged and older men who participated in the Physicians' Health Study, according to the report in the Nov. 22 issue of the Archives of Internal Medicine.
According to the study results, men with a BMI of 28 or greater and who had had a heart attack or stroke did not have a significantly greater risk of death from cardiovascular disease compared with thinner men.
The finding was surprising, said co-author Howard D. Sesso, an assistant professor of medicine at Harvard Medical School. "One always assumes that when we deal with obesity, higher is always worse," he said.
"Our finding doesn't suggest that there are benefits to being heavier," Sesso said. "But that there was no added risk was surprising. Of course, these are men who had likely felt the impact of being obese in the first place."
Sesso believes that some of these men may have lost weight since their heart attack or stroke. In addition, treatment with medication to prevent a second heart attack or stroke may play a role in their reduced risk of death, he said.
It is not clear if the effect is the same for obese women after having a heart attack or stroke, Sesso said.
"It is not our desire to downplay the role of being heavy," Sesso explained. "We would like to replicate these findings," he said.
The Alzheimer's Association can tell you more about keeping your brain fit.