WEDNESDAY, March 26, 2008 (HealthDay News) -- A potbelly in middle age more than triples the risk of senility decades later, according to a large study that pinpoints a new link between obesity and dementia.
"The take-home message is that it's not only what you weigh, but it's where you carry your weight in midlife," said study author Rachel Whitmer, a research scientist with the Kaiser Permanente Division of Research, in Oakland, Calif.
The good news? Lose weight, and you may be able to reduce the increased risk, she said.
Researchers have been tracking the mental fallout of obesity for years. In 2005, Whitmer and her colleagues reported that people who were fatter in middle age were as much as 74 percent more likely to develop dementia as senior citizens.
An estimated 10 million American baby boomers will develop Alzheimer's disease in their lifetime, according to research released earlier this month, while another study found that more than 20 percent of seniors have memory loss not classified as dementia.
In the new study, researchers looked specifically at belly fat, checking to see if it posed a risk in people even if they were otherwise not overweight.
The study examined 6,583 Kaiser Permanente health-care plan members between the ages of 40 and 45 who had their abdominal fat measured in the late 1960s and early 1970s. The researchers followed up to see what happened to them between 1994 and 2006, when they reached their 70s and beyond.
The findings were published in the March 26 online issue of Neurology.
Overall, 16 percent of those studied developed dementia, also known as senility. Researchers found that obese people who had the most abdominal fat in their 40s were 3.6 times more likely to develop dementia than those with the least amount of abdominal fat.
People who were overweight -- a step below obese -- and had large bellies in their 40s were 2.3 times more likely to develop dementia.
Overall, 21 percent of those with high levels of belly fat developed dementia, compared to 15 percent of others, Whitmer said.
The effects of belly fat remained even when researchers adjusted their statistics to take into account the effect of conditions such as stroke and diabetes.
It's still possible that a factor other than abdominal fat may cause the higher rate of dementia. The study doesn't confirm a direct cause-and-effect relationship. Still, the findings suggest that something about abdominal body fat affects the brain independently of cardiovascular disease or diabetes, Whitmer noted.
It's not clear, however, exactly how obesity translates into reduced brain function. It may have something to do with how belly fat surrounds the body's organs and secretes hormones and toxic substances that could disrupt the way the brain functions, Whitmer speculated.
William Thies, vice president of medical and scientific relations with the Alzheimer's Association, said another theory is that the physical presence of belly fat and its compression of abdominal organs could burden the entire body, affecting the brain by increasing blood pressure and cholesterol. However, "whether there's a direct biological link between body fat and Alzheimer's has yet to be established," he said.
Whatever the cause for the connection, all hope is not lost.
"Even with moderate exercise, you can reduce that visceral fat, the fat around the organs," Whitmer said, adding that there's a lot of evidence that the roots of dementia develop years before it becomes obvious, so a change now could spell a big benefit later.
To learn more about proper weight loss, visit the National Women's Health Information Center.