Researchers are using these same participants and MRI technology to determine the risk factors for dementia.
For the first time, researchers are looking at the connection between the protein leptin, produced by fat cells, and Alzheimer's disease.
A new report in the Journal of the American Medical Association finds people with most leptin had the lowest risk for Alzheimer's.
"People in the highest quartile of leptin had only a 6 percent risk of developing dementia over this time over a 12-year period, whereas people in the lowest quartile had a 25 percent risk of developing dementia," said senior study author Dr. Sudha Seshadri, an associate professor of neurology at Boston University School of Medicine.
But the head of UCLA's Mary Easton Center for Alzheimer Research says these findings go against everything we know about Alzheimer's. Previous research shows a rise in weight and blood sugar levels elevates the toxic brain protein that leads to dementia.
"It's at odds with several other observations, that's why it's a stepping stone not an answer," said Dr. Jeffrey Cummings.
The author of the study points out that leptin levels in older adults may serve as one of several possible biomarkers for healthy brain aging.
But Dr. Cummings believes the report raises more questions than answers. Yet he remains optimistic and says findings could be the bridge that leads to potential new therapy.
"We have new relationship between leptin and the likelihood of getting dementia and we need to explore this relationship in greater detail," said Dr. Cummings.