The new study showed that mild Alzheimer's disease patients with higher physical fitness had larger brains compared to mild Alzheimer's patients with lower physical fitness.
Exercising regularly, say researchers, can prevent brain shrinkage in early Alzheimer's disease.
The study was conducted over 121 people age 60 and older. They underwent fitness tests using a treadmill as well as brain scans to measure the white matter, gray matter and total volume of their brains.
Of the group, 57 were in the early stages of Alzheimer's disease while the rest of the group did not have dementia.
"People with early Alzheimer's disease who were less physically fit had four times more brain shrinkage when compared to normal older adults than those who were more physically fit, suggesting less brain shrinkage related to the Alzheimer's disease process in those with higher fitness levels," said study author Dr Jeffrey M. Burns, of the University of Kansas School of Medicine in Kansas City and member of the American Academy of Neurology.
There was no relationship between higher fitness levels and brain changes in the group of people without dementia.
"People with early Alzheimer's disease may be able to preserve their brain function for a longer period of time by exercising regularly and potentially reducing the amount of brain volume lost," Burns said
"Evidence shows decreasing brain volume is tied to poorer cognitive performance, so preserving more brain volume may translate into better cognitive performance," he added.
The study is a published in the July 15, 2008, issue of Neurology(r), the medical journal of the American Academy of Neurology.