People in their early 40s who had a high amount of flab in two different body locations were much more likely to develop Alzheimer's disease more than 25 years later than those with smaller amounts, according to the latest study linking obesity and dementia.
The research is the first to look at how fat distribution around the body during midlife is associated with Alzheimer's risk.
It also advances the understanding that fat is not just inert tissue, but rather is a cell type that can secrete substances that can be harmful to the brain.
The study, which was presented this week at the American Academy of Neurology annual meeting in San Diego, involved 8,776 people ages 40 to 45. Between 1964 and 1973, they all underwent skin-fold testing in which caliper devices were used to measure the thickness of the skin on the triceps (the back of the upper arm) and the back of the shoulders.
Those who had the thickest skin folds in the back of the shoulder were 2.9 times as likely to develop Alzheimer's disease than those who had the least amount of skin fold. In the triceps, the risk was 2.6 times as likely.
"What this is telling us is we need to worry about the disease a lot earlier than we are now," said Sam Gandy, a spokesman for the Alzheimer's Association and a neurologist at Thomas Jefferson University in Philadelphia.
The study adds to the growing amount of research linking Alzheimer's and obesity, as well as related conditions such as high blood pressure and type 2 diabetes.
Medical College of Wisconsin researchers are preparing data showing that memory function in older women may differ depending on where their weight is distributed, said Diana Kerwin, an assistant professor of geriatrics.
"It's not just how much you weigh; it's where the fat is located," Kerwin said. "I think you are going to see more and more papers on this."
Last year, University of Wisconsin-Madison researchers reported finding a link between overweight middle-aged men and amyloid beta, the protein that accumulates in the brains of people with Alzheimer's.
In 2004, Medical College researchers found that women who were overweight or obese throughout adulthood had an increased risk of brain atrophy later in life.
Rachel Whitmer, lead author on the study presented this week, said that if more is not done about the obesity epidemic, the number of cases of dementia in the future may increase more than expected.
About 4.5 million Americans now have Alzheimer's disease.