The study, led by Professor Nicola T. Lautenschlager, the Chair of Old Age Psychiatry at the University of Melbourne, is published in the international journal Journal of the American Medical Association on 3 September 2008.
The Fitness for the Ageing Brain Study, conducted over 18 months at the University of Western Australia, is believed to be the first in the world to demonstrate that moderate exercise can positively affect cognitive function.
Professor Lautenschlager said the results were very promising.
"We found the improvement in memory occurred not only during the six month trial but also 6 and 12 months after completion of the supervised physical activity program'' she said.
"We have known for a long time that exercise is a great way to improve cardiovascular health, but it may be that in the future exercise can also be recommended to protect against the ageing brain."
The trial divided 170 people who had reported memory problems but did not meet criteria for dementia into two groups.
One group continued their usual activities, the other took part in an 24-week home-based physical activity program with the aim to walk three 50 minute sessions or other moderate exercise each week.
Participants in the exercise group did an average of 142 more minutes in a week, or 20 minutes in a day, than those in the control group.
Professor Lautenschlager said by the end of the study, participants in the exercise group performed better on cognitive tests and had better delayed recall. They also had lower Clinical Dementia Rating Scores.
"We believe this trial is the first to demonstrate that exercise can improve cognitive function in older adults at risk,'' Professor Lautenschlager said.
"Unlike medication, which was found to have no significant effect on mild cognitive impairment, physical activity has the advantage of other health benefits such as preventing depression, quality of life, falls, cardiovascular function and disability."
More than 26 million people worldwide have Alzheimer's Disease have dementia. This is expected to grow to 106.2 million worldwide by 2050.
Professor Lautenschlager said if onset of dementia could be delayed by 12 months, there would be 9.2 million fewer cases worldwide.
To organise interviews and pre-records with Professor Nicola Lautenschlager, Chair of Old Age Psychiatry at the University of Melbourne, prior to the journal embargo contact Janine Sim-Jones at the University of Melbourne media unit.
Strictly embargoed until 4am Australian Eastern Standard Time, Wednesday 3 September 2008.