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Experts predict a global epidemic of Alzheimer's disease as the world's population ages. Their focus is now on a fat hormone that may indicate who is more likely to get Alzheimer's or other forms of dementia.

By 2050, the number of people with Alzheimer's is expected to quadruple. In just 40 years, experts say it will increase from one in every 350 people to one in 85. Many will need high levels of care.

Researchers say that dramatically increasing global life expectancy makes it imperative to find solutions that prevent, delay, slow, and treat Alzheimer's disease and related dementias.

"All our brains shrink a little as we grow older, but in some people it shrinks more and [in] some it shrinks less," said Dr. Sudha Seshadri, one of the researchers at Boston University who co-authored a new study on dementia.  "And if it shrinks more, it puts you at higher risk of developing dementia and Alzheimer's."

The study focuses on leptin, a hormone that helps control appetite. Researchers discovered that people whose brains have higher levels of leptin are less likely to suffer from Alzheimer's or other forms of dementia.

The study looked at leptin levels in more than 700 elderly adults who did not have dementia. Eight years later, 200 of the participants had brain scans. The researchers found a link between leptin and dementia.

"People in the highest quartile of leptin had only a six percent risk of developing dementia over this time, over 12 years, whereas people in the lowest quartile had a 25 percent risk of developing dementia," said Dr. Seshadri

Researchers also looked at brain size as these participants aged.

"We also looked at the part of the brain called the hippocampus which is very important for forming the sort of memories we make everyday, you know, when you have to remember a pin number or you have to remember how to get somewhere, and the hippocampus, if it's a good size that means you are less likely to develop Alzheimer's," Dr. Seshadri said.

The report is in The Journal of the American Medical Association.

The scientists say if their work is confirmed, it could lead to further research on how lifestyle choices figure in the prevention and treatment of age-related decline and diseases such as Alzheimer's.