Walking is linked to a reduced risk of dementia, research suggests.
Walking can help the elderly stay alert, say researchers
Two separate US studies, published in the Journal of the American Medical Association, looked at the benefits for men and women.
The study of over 2,000 men over 71 found those who walked least had almost twice the risk of developing dementia than those who walked the most.
A second study of 18,000 women showed those who did more exercise scored better on mental agility tests.
Previous research has suggested that physical activity could be related to dementia risk, but it was not know if the association included low-intensity activity such as walking.
In the study of elderly men, a team from the University of Virginia School of Medicine, Charlottesville, looked at how far they walked per day.
They were monitored from 1991 to 1993. Neurological assessments were carried out between 1994 and 1996, and 1997 to 1999 to see how many had developed dementia.
It was found that, after adjusting for age, men who walked the least, less than 0.25 miles per day, experienced a 1.8-fold increased risk of dementia compared with those who walked more than 2 miles a day.
The association remained after other factors, including the possibility that limited amounts of walking could be the result of a decline in physical function due to preclinical dementia, were accounted for.
Writing in JAMA, the researchers led by Dr Robert Abbott, said: "Although complex, this study and past evidence suggest that walking and active lifestyles in general are associated with a reduced risk of dementia," the researchers conclude.
But they said it was not yet clear why the association existed.
'Three years younger'
In the second study, researchers from Harvard Medical School studied 18,766 women aged 70 and over. They were all taking part in the Nurses' Health Study, a major piece of research which began in 1976.
The women were asked to complete questionnaires every two years, beginning in 1986.
They were then divided into five groups, depending on how much energy they expended.
The researchers found that higher levels of physical exercise were linked to better cognitive performance.
Those in the highest activity grouping also had a 20% lower risk of cognitive impairment than those women in the lowest.
Women who walked at an easy pace for at least 1.5 hours per week had higher cognitive scores than those who walked less than forty minutes per week.
Dr Jennifer Weuve and her colleagues, who carried out the study, said: "The apparent cognitive benefits of greater physical activity were similar in extent to being about three years younger in age and were associated with a 20% lower risk of cognitive impairment.
"The association was not restricted to women engaging in vigorous activities.
"In summary, higher levels of physical activity, including walking, are associated with better cognitive function and less cognitive decline."
Professor Clive Ballard, Director of Research for the UK's Alzheimer's Society, said:" This is potentially a very interesting study, but needs to be interpreted carefully as physical health problems that increase the risk of developing dementia may also reduce physical fitness and walking capacity.
"The authors do not suggest possible mechanisms, but it is certainly becoming increasingly evident that what is beneficial for the heart is also good for the brain, including exercise."
He added: "More speculatively, there is also evidence from some animal studies that exercise increases the number of active stem cells in the brain, which may possibly be relevant to brain protection.
"Although the mechanisms require further study, walking would be generally beneficial as part of a healthy lifestyle, and may also reduce the risk of developing dementia."