New research suggests that walking about five miles a week may help slow the progression of cognitive illness among seniors already suffering from mild forms of cognitive impairment or Alzheimer's disease.
In fact, even healthy people who do not as yet show any signs of cognitive decline may help stave off brain illness by engaging in a similar level of physical activity, the study team noted.
An estimated 2.4 million to 5.4 million people in the United States are believed to have Alzheimer's disease, which causes a devastating, irreversible decline in memory and reasoning, according to the National Institute on Aging.
The researchers presented the findings at a meeting of the Radiological Society of North America (RSNA).
"Because a cure for Alzheimer's is not yet a reality, we hope to find ways of alleviating disease progression or symptoms in people who are already cognitively impaired," lead author Cyrus Raji, MD, PhD, of the department of radiology at the University of Pittsburgh, said in a RSNA news release.
Details of the Study
"We found that walking five miles per week protects the brain structure over 10 years in people with Alzheimer's and MCI, especially in areas of the brain's key memory and learning centers," Dr. Raji said. "We also found that these people had a slower decline in memory loss over five years."
To assess the impact that physical exercise might have on Alzheimer's progression (as well as that of less severe brain illnesses), the researchers analyzed data from an ongoing 20year study that gauged weekly walking patterns among 426 adults.
Among the participants, 127 were diagnosed as cognitively impaired-83 with mild cognitive impairment (MCT), and 44 with Alzheimer's. About half of all cases of MCI eventually progress to Alzheimer's. The rest were deemed cognitively healthy, with an overall average age of between 78 and 81.
A decade into the study, all the patients had 3-D MRI scans to assess brain volume. In addition, the team administered a test called the mini-mental state exam (MMSE) to pinpoint cognitive decline over a five-year period.
After accounting for age, gender, body-fat composition, head size and education, Dr. Raji and his colleagues determined that the more an individual engaged in physical activity, the larger his or her brain volume. Greater brain volume, they noted, is a sign of a lower degree of brain cell death as well as general brain health.
In addition, walking about five miles a week appeared to protect against further cognitive decline (while maintaining brain volume) among those participants already suffering from some form of cognitive impairment.
This indication was bolstered by the mini-mental state exam results, which revealed that cognitively impaired patients who met the walking threshold experienced only a one-point drop in cognition scores over a five-year period. By contrast, those who didn't walk experienced an average decline of five points.
Physical activity had a similar impact on the protection of cognitive abilities in healthy adults, although their exercise threshold was deemed to be about six miles per week of walking.
"Alzheimer's is a devastating illness and, unfortunately, walking is not a cure," Dr. Raji said. "But walking can improve your brain's resistance to the disease and reduce memory loss over time."
Robert Friedland, MD, chairman of the neurology department at the University of Louisville's School of Medicine in Kentucky, expressed little surprise at the findings, but cautioned against inferring a direct cause-and-effect link between walking and protection against cognitive decline.
"In an observational study like this, undoubtedly people who are developing cognitive disease or are likely to be in the early stages are also likely to become less active," he noted. "So, it's not possible to be sure that they're observing a direct effect of walking on the disease, because diminished walking in the group that is progressing more rapidly could have been a direct result of the disease itself.
"But that's not to say that I don't think walking is a good idea," Dr. Friedland added. "Many people, including my group, have shown that physical as well as mental activity may be protective against developing disease during midlife-that is, between [ages] 20 and 60. And I'm sure that this is also true in later life.
"And there are many reasons why. Physical activity improves blood flow to the brain, and it changes neurotransmitters and improves cardiac function," he said. "It lessens the risk of obesity, improves insulin resistance and lowers the risk of diabetes, and lowers your blood pressure. And all of these things are risk factors for Alzheimer's disease.
"So, I would say that everyone at all ages should be encouraged to get as much physical exercise as they can tolerate," Dr. Friedland concluded. "Of course, we don't want people to exercise excessively if they have heart disease, for example. But with a physician's advice and supervision, walking is an excellent form of activity."
Since the research was presented at a medical meeting, the data and conclusions should be seen as preliminary until published in a peer-reviewed journal.