Regular physical activity -- even walking -- may be key to maintaining a sharp mind as we get older, two new studies suggest.
While that's not a new discovery, the studies plug critical gaps in the scientific literature and corroborate previous reports linking exercise to reduced rates of mental impairment in older adults.
The message is now clearer than ever: "If you stay physically active, you're buying protection for your brain," says Eric B. Larson, M.D., the vice president for research at Group Health Cooperative, a nonprofit health-care system based in Seattle.
The studies appear in the July 25 print edition of the Archives of Internal Medicine and were published online today to coincide with the International Conference on Alzheimer's Disease, taking place this week in Paris.
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One of the studies included 2,809 women over the age of 65 who had a history of heart disease or stroke, or at least three risk factors for those conditions. That's noteworthy because most previous studies on exercise and dementia have focused on healthy people, according to Dr. Larson, who wrote a commentary accompanying the new research.
Exercise may be particularly important for these women, since unhealthy cholesterol levels, high blood pressure and other conditions that affect blood-vessel health have been linked to the memory and language problems known as cognitive decline, which often precedes Alzheimer's disease and other forms of dementia.
Researchers in Paris and at the Harvard School of Public Health, in Boston, reanalyzed data from a study originally designed to examine the role of antioxidant vitamins in heart health.
Beginning in 1995, the women answered biennial surveys on how often they engaged in various types of exercise (such as jogging, swimming, walking, and climbing stairs). Several years later, the researchers then gave them a series of telephone-based cognitive and memory tests on four separate occasions spread out over a four- to six-year period.
The more active the women were, the better their performance on the test. And they didn't have to be marathoners. The most active women, who were getting the equivalent of 30 minutes or more of brisk walking every day, experienced much slower cognitive decline than those who got little or no exercise. According to the researchers, the difference amounted to being five to seven years younger, cognitively speaking.
The strong link between activity and a lower risk of cognitive decline was all the more notable given the "very crude" telephone tests used by the researchers, Dr. Larson says.
A second, smaller study addressed a common weakness of the existing research on exercise and dementia: the reliance on the participants' own description of their exercise habits, which can be unreliable.
In addition to using surveys, researchers used various laboratory tests to gauge the total amount of energy expended by 197 men and women in their 70s over a two-week period. The tests involve drinking chemically altered water and measuring (via blood and urine samples) how quickly the body breaks down the chemicals.
Compared with more sedentary individuals, the people who expended the most energy over the two weeks had 90 percent lower odds of developing cognitive decline over the five- to seven-year follow-up period -- a "really strong" reduction in risk, says the lead researcher, Laura E. Middleton, Ph.D., an assistant professor of kinesiology at the University of Waterloo, in Ontario.
What's more, the participants’ lab-tested energy expenditure was more closely linked with cognitive health than their subjective accounts of how much exercise they typically get, which suggests that everyday activity, and not just exercise, may help maintain brain health.
"It's not only that type of purposeful physical activity that's important; it's also the less intense work ... stuff like just standing up more often and walking more often," Middleton says.
"It's bad news for those of us, including myself, who sit at a desk all day," she adds. "It means that we really need to find some way to get up and move."