Physical exercise may help improve memory in older people and delay the onset of dementia, a new study published in the Journal of the American Medical Association shows.

A University of Western Australia study has found that walking for 50 minutes three times a week can lessen memory problems for older people. The study involved 170 volunteers aged 50 and over who reported some memory trouble but who did not have dementia.

The number of people with Alzheimer’s disease, the most common form of dementia, is predicted to quadruple worldwide over the next half century. Alzheimer’s is a terminal and degenerative disease for which there is known no cure. In its common form, it affects people over 65 years old. The most commonly symptom is memory loss, as well as the difficulty to remember recently learned facts. Studies have shown that 700,000 in the UK live with dementia and the number may increase over the next two decades.

During the study some volunteers were asked to complete three 50-minute sessions of moderate physical activity (such as walking) a week for 24 weeks. The others did not exercise.

After six months, the participants were given memory and other tests, including recalling lists of words. Those who exercised achieved better scores in tests of their cognitive function. The benefits persisted for at least another 12 months after the end of the exercise programme.

“This study demonstrates that exercise improves cognition in people with mild cognitive impairment, and that there is a lasting effect even after the exercise intervention stops,” Dr. Susanne Sorensen, head of research at the Alzheimer’s Society, said.

Professor Lautenschlager, who led the project, says researchers are now going to look at whether exercise can also help those already diagnosed with dementia or Alzheimer’s disease.

Exercises make the blood flow to the brain faster and deliver oxygen and nutrients to brain cells. Decreasing brain volume is strictly tied to poorer cognitive performance, so preserving more brain volume will give better cognitive performance. The other explanation is that exercises change directly, on a cell level, the metabolism of the brain cells, Professor Lautenschlager said.

According to the World Health Organization, there are about 18 million people worldwide with Alzheimer’s disease. By 2025, that number is expected to reach 34 million, as existing drugs can ease symptoms but do not stop the disease.

The fact that physical exercise is good for the body, reducing anxiety and depression, particularly in older people, is not a secret anymore. Previous studies showed that physical exercise has a positive effect on hippocampus, the part of the brain responsible for both memory and balance. In Alzheimer’s, the hippocampus is one of the first regions of the brain affected by the disease.

As the number of patients with Alzheimer’s disease is going to quadruple worldwide by 2050 reaching approximately 106 million cases, the researchers are trying to find ways to help delay the onset of dementia.

Studies presented at the 2008 International Conference on Alzheimer’s Disease in Chicago also showed the benefits of physical exercises for people with early Alzheimer’s.