Walking six miles a week may help prevent the brain shrinking in old age and preserve memory, according to scientists.
Researchers studied 299 healthy older people who recorded the distances they walked in a week.
Nine years later, the volunteers were given scans to measure their brain size. Then after another four years they were tested to see if they were suffering from mental decline or dementia.
The first test showed that people who walked at least six to nine miles per week had more “grey matter” in their brains than those who did not.
Grey matter consists of the cell bodies of neurons, rather than the fibres that transmit signals.
Walking greater distances did not appear to preserve grey matter any further.
By the time the mental tests were carried out, 116 of the participants – or 40% - had developed some degree of dementia or cognitive impairment. But those who had walked the most were half as likely to be experiencing memory problems.
The findings have been reported online in the journal Neurology.
Brain shrinkage is known to be a normal part of ageing and is linked to age-related mental decline.
Study leader Dr Kirk Erickson, from the University of Pittsburgh in the US, said: “Brain size shrinks in late adulthood, which can cause memory problems. Our results should encourage well-designed trials of physical exercise in older adults as a promising approach for preventing dementia and Alzheimer’s disease.
“If regular exercise in mid-life could improve brain health and improve thinking and memory in later life, it would be one more reason to make regular exercise in people of all ages a public health imperative.”