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March 26, 2008 -- Having a fat belly at midlife, which is already associated with an increased risk of diabetes, heart problems, and stroke, also increases the risk of getting dementia in your later years, according to a new study.
"This is the first time research has linked central obesity in midlife with dementia later in life," says Rachel Whitmer, PhD, research scientist at the Kaiser Permanente Division of Research in Oakland, Calif., who led the study. Central obesity is the term used for excess abdominal body fat.
"Where you carry your weight is an important risk factor," she tells WebMD. "If you are overweight and carry it in your belly, you are at greater risk [of health problems] than someone overweight who doesn't carry it in their belly."
Whitmer and her colleagues followed the medical records of 6,583 members of Kaiser Permanente of Northern California, a large health maintenance organization, for an average of 36 years, from the time they were in their 40s until they were in their 70s.
They looked at medical exam records from visits between 1964 and 1973, when the members were in midlife (40-45 years old), and then again from 1994 to 2006. At the exams, the Kaiser members provided information on lifestyle, height, and weight and had the diameters of their bellies measured.
Whitmer's team divided the participants into five groups -- from those with the least amount of belly fat to those with the most.
The measurement taken, called the sagittal abdominal diameter, measures the belly from front to back, she says, and isn't easily translated into waist size. A sagittal abdominal diameter of 25 centimeters or more is considered high and reflects excess fat. They didn't collect waist circumference measurements.
Over the course of the study, 1,049 participants were diagnosed with dementia, including Alzheimer's disease.
The bigger the belly, the higher the risk of dementia, they found.
"We found that people who were in the upper 20% of the belly size had a 2.72 times greater risk of dementia, compared to people in the bottom 20%," Whitmer says.
Not everyone who is overweight has a big belly, and some normal-weight people carry excess belly fat. So the researchers looked at the effects of both weight and belly fat.
The worst scenario was being obese with a lot of belly fat. "If you are obese with a big belly, the risk of dementia is 3.6 times [the risk of those with normal weight and low belly fat," Whitmer tells WebMD.
People of normal weight but with excess belly fat had a 1.89 times higher risk of getting dementia than those of normal weight and no excess belly fat.
The study is published online in Neurology.