Exercise may prevent damaging changes in the brain that are associated with Alzheimer's, thereby lowering the risk of developing the disease, a new study involving mice suggests.

Exercise also seemed to increase the rate of learning among mice bred to have Alzheimer's-like symptoms, the scientists said.

In the study, researchers showed that long-term physical exercise decreased the level of plaque-forming beta-amyloid protein particles, which are characteristic of Alzheimer's.

The findings appear in the April 27 issue of The Journal of Neuroscience.

"This is the first study to show that exercise is sufficient to decrease the number of plaques in the brain as well as increase the rate of learning," said lead researcher Paul A. Adlard, a post-doctorate fellow at the University of California, Irvine.

Adlard and his colleagues worked with mice especially bred with the human gene that produces the beta-amyloid protein. "The mice are similar to Alzheimer's disease patients," he said.

When the mice were about four to six weeks old, they were placed in cages with or without exercise wheels. Those that had the wheels were allowed to exercise for either one month or five months, anytime they wanted. Those without wheels were considered sedentary subjects.

Periodically, the animals' ability to learn was tested by placing them in a water maze. The animals that exercised mastered the maze faster, the researchers report. Mice that used the running wheels for five months took less time to learn the maze than mice that didn't exercise. This finding may mean that exercise can help to offset learning and cognitive problems suffered by Alzheimer's patients, the researchers said.

After five months, Adlard's team also examined tissues from the brains of mice that had exercised. "These mice had almost 50 percent fewer plaques than mice that did not exercise," he said.

Why exercise has this effect remains a mystery, Adlard said. "However, the exciting thing about this is it is giving scientific credence to a lot of anecdotal evidence," he noted. "This study demonstrates that a small change in lifestyle does have a scientific basis for perhaps being able to prevent Alzheimer's disease."

Adlard added, however, that it is not yet clear how this animal study might translate to humans. The amount of exercise needed for people to achieve the same benefits is unknown. Another unknown -- how early in life exercise should be started, he said.

Dr. David A. Bennett, director of the Rush Alzheimer's Disease Center in Chicago, called the findings "fascinating."

Bennett said he is doing studies with more than 1,000 healthy people to see how lifestyle affects the development of Alzheimer's. "The people in the study have agreed to brain donation, so after they die, we can measure amyloid deposits," he said.

Bennett hopes to find that lifestyle changes can reduce a person's risk of Alzheimer's. "There is clearly something to these lifestyle changes," he said. "The question is whether or not it's affecting disease pathology itself."

While lifestyle changes may prevent Alzheimer's, it's doubtful they can help Alzheimer's patients, Bennett said. "For example, cigarette smoking increases your risk for lung cancer, but once you have lung cancer, cigarette smoking really doesn't have much effect," he added.

However, new hope for those with Alzheimer's comes from research results just reported in the April 24 online issue of the journal Nature Medicine.

The study results suggest that gene therapy could slow the progression of Alzheimer's by stopping brain cells from dying.

Of the seven surviving patients who had a protein known as nerve growth factor implanted into their brains in 2001 and 2002, tests suggested the procedures may have slowed their mental decline by 36 percent to 51 percent. In addition, PET scans revealed that some of the patients' brains were using more glucose, a possible sign of increased mental activity.

"Our hope is that these findings mean people can remain more functional in their home setting for a longer period of time and have an improved quality of life," said Dr. Mark Tuszynski, a professor of neurosciences at the University of California, San Diego, and co-author of the study.

More information

To learn more, visit the Alzheimer's Association.