OAKLAND, CA -- People in their 40s with larger stomachs have a higher risk for dementia when they reach their 70s, according to a study published in the March 26 online issue of Neurology.

Previous studies have looked at central obesity (as determined by waist circumference) and body mass index in the elderly and its link to dementia risk and found that a large abdomen—in midlife—increases the risk of diabetes, stroke and coronary heart disease. However, this is the first time researchers have demonstrated an association between midlife belly fat and the risk of dementia.

Capturing abdominal obesity in midlife may be a much better indicator of the long-term metabolic dysregulation that leads to dementia risk, says study author Rachel Whitmer, a research scientist at the Kaiser Permanente Division of Research in Oakland, CA. Measuring abdomen size in older people may not be as good an indicator because as people age, they tend to naturally lose muscle and bone mass and gain belly size, she says.

“Considering that 50 percent of adults in this country have abdominal obesity, this is a disturbing finding,” she says. “It is well known that being overweight in midlife and beyond increases risk factors for disease. However, where one carries the weight—especially in midlife—appears to be an important predictor for dementia risk.”

Autopsies have shown that changes in the brain associated with Alzheimer’s disease may start in young to middle adulthood, and another study showed that high abdominal fat in elderly adults was tied to greater brain atrophy, Whitmer says. These findings suggest that the dangerous effects of abdominal obesity on the brain may start long before the signs of dementia appear. Researchers note that additional research needs to be completed to determine the underlying mechanisms that link abdominal obesity in midlife to dementia risk.

Researchers studied 6,583 people ages 40 to 45 in Northern California. Belly fat was measured by using calipers to determine the distance from the back to the upper abdomen, midway between the top of the pelvis and the bottom of the ribs. Belly density is highly correlated with visceral fat tissue, which is the fat tissue that is wrapped around the organs, researchers note. 

The study found that those who were overweight and had a large belly were 2.3 times more likely to develop dementia than people with a normal weight and belly size. People who were both obese and had a large belly were 3.6 times more likely to develop dementia than those of normal weight and belly size. Those who were overweight or obese but did not have a large abdomen had an 80 percent increased risk of dementia.

Having a large abdomen increased the risk of dementia regardless of whether the participants were of normal weight overall, overweight or obese, and regardless of existing health conditions, including diabetes, stroke and cardiovascular disease. Non-whites, smokers, people with high blood pressure, high cholesterol or diabetes, and those with less than a high school level of education were also more likely to have abdominal obesity.

Researchers note that, as with all observational studies, it is possible that the association of abdominal obesity and dementia is not driven by abdominal obesity but rather by a complex set of health-related behaviors, for which abdominal obesity plays one part.

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