Analysis found that participants who were more physically fit had less brain shrinkage than less-fit participants.

However, they didn't do significantly better on tests for mental performance.

That was a surprise, but maybe the study had too few patients to make an effect show up in the statistical analysis, said Dr. Jeffrey Burns, one of the study's authors.

He also stressed that the work is only a starting point for exploring whether exercise and physical fitness can slow the progression of Alzheimer's. The study can't prove an effect because the participants were evaluated only once rather than repeatedly over time, he said.

While brains shrink with normal aging, the rate is doubled in people with Alzheimer's, he said.

Burns, who directs the Alzheimer and Memory Program at the University of Kansas School of Medicine in Kansas City, reports the work with colleagues in Tuesday's issue of the journal Neurology.

The study included 57 people with early Alzheimer's. Their physical fitness was assessed by measuring their peak oxygen demand while on a treadmill, and brain shrinkage was estimated by MRI scans.

Dr. Sam Gandy, who chairs the medical and scientific advisory council of the Alzheimer's Association, said the result fits in with previous indications that things people do to protect heart health can also pay off for the brain.

---