Sci. Aging Knowl. Environ., 24 November 2004
Pay by the Pound
Added weight might take a toll on the brain
Packing extra pounds burdens the heart, forces the kidneys to labor harder, and strains the joints. It might also promote shrinkage of a brain region involved in memory, according to a new study.
Researchers have been amassing evidence that the harmful effects of excess body fat could be going to our heads. Last year, for example, epidemiologist Deb Gustafson of Sahlgrenska University Hospital in Göteborg, Sweden, and colleagues showed that overweight women were more likely to develop Alzheimer's disease (AD) than women of normal weight. And a study reported earlier this month suggests a link between brain deterioration and metabolic syndrome, a disorder characterized by fat around the middle, high blood pressure, insulin resistance, and systemic inflammation (see Hornsby Review). Elderly men with metabolic syndrome scored lower on a test of mental acuity than did men without the disorder. Gustafson and colleagues wanted to explore whether added bulk plays a role in brain decline.
The team used data from a Swedish project that, in the late 1960s, began tracking the health of 1462 women who were between 38 and 60 years old. The women regularly received medical exams and filled out health questionnaires. In the early 1990s, some participants who were between 70 and 84 years old also underwent computed tomography (CT) scans of the brain and psychiatric exams, including tests to detect dementia. Gustafson and colleagues compared the amount of brain deterioration visible in the CT scans with the women's body mass index (BMI), an indicator of total body fat. Women who displayed shrinkage of the temporal lobe, a brain region that helps etch memories and is one of the first areas to show damage in AD, had a higher BMI. The scientists observed the effect even when they factored out variables such as smoking, blood pressure, and age.
Some studies have suggested that abdominal fat is particularly harmful. However, the team found no connection between brain breakdown and waist-to-hip ratio, an indicator of this central padding. The women with brain declines weren't all overweight, says Gustafson, but they were heavier than women who didn't show the change. The researchers aren't sure how extra weight affects the brain, but it might promote strokes that kill cells or trigger release of stress hormones that damage neurons. At the next checkup, in 2005, the team will be able to determine whether the withering measured a decade ago presaged mental decline.
Combined with the team's previous work, the results "help build the case that obesity and being overweight are risk factors not just for cardiovascular disease but also for dementia," says epidemiologist Peter Zandi of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland. "It fits with a growing trend in the literature," agrees neuroscientist William Jagust of the University of California, Berkeley. The next challenge is to pin down the mechanism, he says, and researchers might already have the data at hand. To find whether the deterioration stems from stress or inflammation, for example, scientists could test blood samples for high concentrations of stress hormones or inflammation-promoting molecules. That work might show how adding to our bodies subtracts from our brains.
November 24, 2004
Science of Aging Knowledge Environment. ISSN 1539-6150