Taking a brisk walk or engaging in other moderate-intensity physical activities may help slow down the progression of Alzheimer's disease in people who are already at a risk of developing the disorder, a study claims.

Researchers from University of Wisconsin-Madison in the US studied about 93 members of a parental history Alzheimer's risk study group.

They measured the daily physical activity of participants, all of whom were in late middle-age and at high genetic risk for Alzheimer's disease, but presently show no cognitive impairment.

Activity levels were measured for one week, quantified, and analysed. This approach allowed researchers to determine the amount of time each subject spent engaged in light, moderate, and vigorous levels of physical activity.

Light physical activity is equivalent to walking slowly, while moderate is equivalent to a brisk walk and vigorous a strenuous run.

Data on the intensities of physical activity were then statistically analysed to determine how they corresponded with glucose metabolism - a measure of neuronal health and activity - in areas of the brain known to have depressed glucose metabolism in people with Alzheimer's disease.

Researchers measured brain glucose metabolism using a specialised imaging technique called 18F-fluorodeoxyglucose positron emission tomography (FDG-PET).

They found moderate physical activity was associated with healthier (greater levels of) glucose metabolism in all brain regions analysed.

Researchers also noted a step-wise benefit: subjects who spent at least 68 minutes per day engaged in moderate physical activity showed better glucose metabolism profiles than those who spent less time.

"While many people become discouraged about Alzheimer's disease, these results suggest that engaging in moderate physical activity may slow down the progression of the disease," said Ryan Dougherty from University of Wisconsin- Madison.

The study was published in Journal of Alzheimer's Disease.