A study has shown that walking between six and nine miles a week can protect the brain against shrinkage in old age.

The US study on 300 volunteers over a 13 year period determined that walking helps one fight against several memory problems which, among others, include dementia and Alzheimer's.

Walking may actually protect the brain from shrinking and preserve memory in elderly people, said neurologists who were involved in the research.

Neurological tests were performed on dementia-free people in Pittsburgh who agreed to log their walks and receive brain monitoring in 1995. The participants received more testing nine years later and then again in 2008.

The results of the follow-up tests showed that those who walked the most cut their risk of developing memory problems by 50 percent.

"We have always been in search of the drug or the magic pill to help treat brain disorders," said Kirk I. Erickson, the study's lead author and assistant professor of psychology at the University of Pittsburgh.

"But really what we are after may be, at least partially, even simpler than that. Just by walking regularly, and so maintaining a little bit of moderate physical activity, you can reduce your likelihood of developing Alzheimer's disease and spare brain tissue”, he added.

According to neurologist recommendations the optimum distance for brain health is around 9 miles per week.

According to reports published in Neurology, additional walking after the nine mile mark showed no discernible bonus.