Regular aerobic exercise can facilitate reversal of the mental decay that comes with ageing even in people with Alzheimer's, a study has suggested.

The findings of the research, published in the 'British Journal of Sports Medicine', suggested that aerobic exercise can improve the functioning of older brains. As of 2008, more than 500 clinical trials were investigating possible treatments for Alzheimer's disease.

"We can safely argue that an active lifestyle with moderate amounts of aerobic activity will likely improve cognitive and brain function, and reverse the neural decay frequently observed in older adults," said Professor Art Kramer, from the US Beckman Institute at the University of Illinois.

Alzheimer's disease is a common form of dementia. An estimated 26.6 million people worldwide were afflicted with Alzheimer's in 2006, with the number expected to quadruple by 2050.

As the disease advances, symptoms include confusion, irritability and aggression, mood swings, language breakdown, long-term memory loss, and the general withdrawal of the sufferer as their senses decline.

Professor Kramer underlined that around six months of moderate aerobic activity would be enough to see a marked improvement in brain power. Its effect also "seems to extend to older adults with dementia".

The findings suggested that people who exercised for just one hour three times a week over three months increased their brain size to that of someone three years younger, the Daily Telegraph said. The report in the British daily said exercise can help older brains retain the capacity to grow and develop, known as plasticity.