People who have higher levels of an appetite-suppressing hormone produced by fat cells may be less likely to develop Alzheimer's disease or dementia than others, U.S. researchers said Tuesday.

They said people in a study who had the highest levels of leptin were far less likely to develop Alzheimer's disease or any sort of dementia than those in the study with the lowest levels of leptin.

People with higher leptin levels also had more brain volume at the end of the study, something that is lost in people with Alzheimer's, a mind-robbing form of dementia that affects more than 26 million people globally.

"What we found is that people with higher leptin levels at baseline had a lower risk of developing Alzheimer's disease and dementia," Dr. Wolfgang Lieb of Boston University, whose study appears in the Journal of the American Medical Association, said in a telephone interview.

The discovery of leptin in 1995 raised hopes for a natural weight loss tonic. Obese mice that lacked leptin lost weight on the stuff. But in obese humans, leptin only brought temporary success.

Lieb and colleagues drew on data from the Framingham Heart Study, a giant health study begun in Framingham, Massachusetts in 1948, with which Lieb is affiliated.

The team looked at the relationship between leptin concentrations in the blood and Alzheimer's disease and other forms of dementia in 785 people who started out with no signs of dementia in 1990 to 1994.


Nearly 200 of these people also had brain scans to measure their brain volume. After an average of 8 years and for some people as long as 15 years, 111 people developed dementia, and 89 of these were diagnosed with Alzheimer's disease.

The team found that a person who started out with the lowest leptin levels had a 25 percent risk of developing Alzheimer's, while a person who started with the highest leptin levels had only a 6 percent risk of developing Alzheimer's or dementia.

And of those who had brain scans, people with higher leptin levels had more brain volume in the hippocampus — a key memory center of the brain — compared with people who started with lower leptin levels.

Lieb said lab experiments and studies in mice suggest that leptin plays a role in cognitive function. He said the current findings suggest that leptin may play a broader role in the body than just regulating appetite.

"It could be this is a potential biological pathway that could be involved in developing Alzheimer's disease," Lieb said.

Curiously, the association between leptin levels and dementia was not statistically significant in obese people, but this was a small part of the overall study.

Lieb said obese people tend to have high levels of leptin, but scientists believe they develop resistance to it, which could explain this result.