July 20, 2011 (Paris) -- Two new studies add to growing evidence that physical activity helps to keep older people's brains sharp.
Neither study shows cause and effect, only that there is an association between exercise and cognitive health.
But in both studies, participants who exercised the most were substantially less likely to suffer memory loss and other signs of cognitive decline, compared to their more sedentary counterparts.
"Most importantly, the association [between slower cognitive decline] and physical activity was not limited to people engaged in vigorous exercise," says researcher Marie-Noël Vercambre, PhD, of the Foundation of Public Health at Mutuelle Generale de l'Education Nationale in Paris.
Even taking a brisk, 30-minute walk every day was associated with a lower risk of cognitive impairment, she tells WebMD.
Both studies were presented at the Alzheimer's Association International Conference here and simultaneously published online in the Archives of Internal Medicine.
Older Women With Heart Problems Benefit
Vercambre and colleagues at Harvard Medical School examined the effect of physical activity on mental decline among about 2,800 women aged 65 and older participating in the Women's Antioxidant Cardiovascular Study.
All had cardiovascular disease or at least three risk factors for heart disease, placing them at substantially higher risk of cognitive decline, she says.
Participants filled out questionnaires on their recreational physical activities, such as walking, bicycling, and stair climbing, at the start of the study and every two years afterward. Then they were divided into five groups based on how active they were.
Participants also were given a battery of cognitive tests, at the study's outset and three more times over the next five or so years. The tests measured memory, the ease with which one could complete a given task, and other mental skills.
Results showed that women in the highest two-fifths of physical activity had substantially lower rates of cognitive decline than women in the lowest exercise bracket.
"There is a strong association between greater physical activity and reduced cognitive decline in women with vascular disease or coronary risk factors," Vercambre says.
Taking a half-hour brisk walk, or its equivalent, each day appears to delay mental aging by five to seven years, she says.
The researchers point out that the study has several limitations, including use of telephone interviews for some cognitive testing and potentially unreliable self-reporting of physical activity by the older participants.
A More Objective Measure of Physical Activity
In the second study, researchers used a more objective measure of energy expended during physical activity, employing the so-called doubly labeled water technique to determine how much water a person loses.
The study involved 197 men and women participating in the larger Health, Aging, and Body Composition study. Participants, whose average age was 75 years, had no mobility or cognitive problems when the research began.
Over the next two to five years, those in the highest third of energy expenditure were substantially less likely to develop clinical cognitive impairment than those in the lowest third.
Cognitive function was measured using the Mini-Mental State Exam (MMSE), a brief test of mental skills, including attention span and memory.
About 2% of people in the highest third suffered declines in cognitive function, compared with 5% in the middle third and 17% in the lowest third.
In a surprising finding, the participants' levels of energy expenditure did not completely correlate with how much physical activity they reported they did.
The results were reported by Laura Middleton, PhD, of Sunnybrook Health Sciences Centre in Toronto.
Exercise Good for Everyone
In an editorial accompanying the studies, Eric B. Larson, MD, MPH, of Group Health Research Institute in Seattle, said exercise "is definitely worthwhile" no matter what one's age and "is likely to be of increasing benefit as [one] advances into old age."
Ronald Peterson, MD, director of the Mayo Alzheimer's Disease Research Center at the Mayo Clinic in Rochester, Minn., tells WebMD that physical activity improves the flow of blood in the brain. Also, animal studies suggest that exercise may release enzymes into the brain that attach and destroy Alzheimer's-associated plaque, he says.