Those over 50 and forgetful might want to consider leaving their car at home and stretching their legs instead.

Australian researchers have found that walking for two and a half hours a week can improve memory problems.

The study, published in the Journal of the American Medical Association, is one of a growing number of studies linking moving the body to a healthier brain.

"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," professor Nicola T. Lautenschlager, lead author of the study, said.

Researchers divided 170 people with reported memory problems into two groups. One group continued their everyday lives as usual, while the other took part in a 24-week home-based physical activity program. The group was asked to walk for 50 minutes three times a week or complete some other form of moderate exercise.

Those in the exercise group did an average of 20 minutes more a day, than those in the other group.

"We found the improvement in memory occurred not only during the six month trial but also six and 12 months after completion of the supervised physical activity program,'' Lautenschlager said.

By the end of the study, people who exercised...

  •  did better on brain tests
  •  improved their memories 
  •  had fewer signs of dementia

"We believe this trial is the first to demonstrate that exercise can improve cognitive function in older adults at risk,'' 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 or dementia. That number is expected to grow to more than 106 million by 2050.

There would be 9.2 million fewer cases worldwide if onset of dementia could be delayed by 12 months, Lautenschlager said.