As little as 20 minutes a day of aerobic exercise could help people over 50 improve their memory, a new study suggests.

Results of the randomized control trial study appear in Wednesday's issue of the Journal of the American Medical Association.

Dr. Nicola Lautenschlager of the University of Melbourne and her colleagues tested whether exercise would reduce the rate of cognitive decline among 138 people over 50 at increased risk for dementia. Half were randomly assigned to an education group, and the rest participated in a 24-week physical activity program.

"What our trial tells us is that older people who take up some form of aerobic exercise for as little as 20 minutes a day will be more likely to remember things like shopping lists, family birthdays and friends' names," said study author Prof. Leon Flicker of the Western Australian Institute for Health and Aging.

"What's interesting about this study is that physical activity doesn't just have benefits for memory and preventing Alzheimer's disease, it highlights the importance of exercise to boost overall well-being and mental health."

Medications approved to aid mental function in Alzheimer's disease had "no significant effect on mild cognitive impairment at 36 months," the researchers said, while physical activity not only helped cognitive function, but also depression, quality of life and cardiovascular function.

The results don't prove that exercise leads to improvements in brain function or memory. And while the hope is that exercise may reduces the risk of dementia or Alzheimer, the memory test findings can't be applied to those diseases, the researchers cautioned.

Preventive approach

Study participants said they had memory problems but did not have dementia. The subjects were aged 50 or older. Half were randomly assigned to do at least 2½ hours of physical activity a week for six months. Those in the control group were not asked to exercise.

People in the exercise group were asked to keep track of their activity. Most walked, but the activities ranged from ballroom dancing to swimming.

All participants had their cognition tested over the 18-month study period.

After six months, the exercise group performed 1.3 points better on a 70-point scale of brain function than the non-exercise group. By 18 months, the difference in benefits narrowed to 0.69 points, the researchers found.

"It's an important piece in that it's the first intervention in people with memory complaints that's showing some potential benefit," said Dr. Raj Shah, director of the memory clinic at Rush University Medical Center in Chicago. He was not involved in the study.

Larger studies are needed before doctors would prescribe physical activity to treat memory problems, Shah added. Dr. Ron Petersen of the Alzheimer's Association agreed, saying he would use the results when talking about the potential benefits of exercise with patients.

"Health advances of the past century have led to more individuals surviving to extreme old age, when their risk of Alzheimer disease and related dementias increases substantially," Dr. Eric Larson of the Group Health Center for Health Studies, Seattle, said in an editorial accompanying the study.

"Exercise — and possibly other lifestyle factors — appear to affect vascular risk and late-life brain health. In addition to traditional medical approaches to prevent this dreaded disease, social factors such as providing universal education, general medical care, a suitable environment, adequate nutrition, habitual exercise, and opportunities for continued social interactions throughout the lifespan also may contribute significantly to improve well-being in late life."

An earlier study of patients with early Alzheimer's disease found those who exercised regularly experienced less deterioration in the areas of the brain that control memory, based on magnetic resonance imaging.

With files from the Associated Press