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January 5, 2017

Physical activity reduces the risk of cognitive impairment: But how does it work?


Jogging Seniors
Full length of senior man exercising on stationary bike in health club

Greater amounts of physical activity can cut in half our risk of developing cognitive impairment as we age. But how does it work — and is it the real cause of such improvements?

Those are the questions Kirk Erickson, psychology faculty member in the Dietrich School of Arts and Sciences and director of the Brain Aging and Cognitive Health Lab, sought to address for a packed December talk sponsored by the mental health and wellness task force of the University Senate benefits and welfare committee.

Exercise is almost universally promoted as a healthy endeavor, but can it be credited with specific improvements in brain function? Are physically active people just healthier eaters, for instance?

A 2013 meta-analysis of physical fitness programs and brain function showed that “exercise training improves cognitive function in older adults,” Erickson said. It creates specific effects on the prefrontal cortex, for instance, and most significantly the hippocampus.

The hippocampus helps with our memory function, and declines in hippocampal function are associated with Alzheimer’s disease.

But even in cognitively normal adults, hippocampal volume — as measured by magnetic resonance imaging, or MRI — declines 1-2 percent a year during the aging process. A recent study of 165 adults, Erickson said, showed that their cardiovascular fitness levels correlated with hippocampus volume. Those with greater fitness levels had larger hippocampal volumes and better blood flow in that part of their brains as well.

“This is a very provocative association,” he said. “It’s been replicated in other samples” — children, adolescents, even people who already have Alzheimer’s.

Overall, he said, it appears that exercise could prevent, delay or treat cognitive diseases. But how does this happen?

Senior Stretches“If we get people more active, can we modify the size of the hippocampus?” he asked. Can we keep it from naturally shrinking, or make it grow back after deterioration?


In 2011, Erickson’s lab designed an exercise intervention for older, sedentary adults to test these questions.

“Unfortunately, older, inactive people are not that hard to find,” he noted.

The study subjects were randomized to two groups: those undertaking the moderate exercise of brisk walking and those doing the light exercise of stretching and toning.

At the completion of the program, after a battery of tests, overall fitness improved nearly 8 percent for the walking group and just over 1 percent for the stretching group.

More significantly, measures of subjects’ brains showed that the hippocampus in the average walking group member increased in size, reversing the normal aging process for that part of the brain. The result was, Erickson said, “like rolling back the clock one or two years.” The hippocampus of stretching group members declined an average of 1.5 percent: they simply aged normally.

Looking at other studies, Erickson sees similar results: The better the fitness improvement, the greater the hippocampus size increase.

“Tennis has the same effect,” he said. “We really don’t know, but we believe it has to do with the intensity of activity [and] getting your heart rate up” during an aerobic exercise.


Of course, he added, improving one aspect of your health naturally will affect other body functions: “These are not mutually exclusive.”

Very few organs in your body are unimproved by increased physical activity, Erickson noted. “We’re never going to find the one molecular pathway that is the key” to reversing the aging process, he said. “Becoming physically active influences a host of different areas” in your body and your life, such as how well you sleep and how frequently you are depressed.

“Maybe exercise is a great way to get everyone to sleep better … or a great way of getting you to feel better,” he suggested.

That hasn’t stopped scientists from seeking a single answer to the fitness/health association. Researchers currently are studying the brain-derived neurotrophic factor (BDNF), which is involved in the production of new neurons, as one mechanism that may translate exercise into improved brain health.

In rodents, exercise produces new blood flow in the brain and more neurons in the hippocampus, improving the memory and increasing the secretion of BDNF. In humans, BDNF helps protect us from stroke and depression and reduces amyloid deposits in the brain, which are associated with Alzheimer’s.

Researchers also have examined the effect of exercise on those who are at greater risk of Alzheimer’s due to APOE. The APOE gene helps us make lipoproteins, which carry fats through our bloodstream and affect our cardiovascular health.

Higher APOE levels also put us at greater risk for Alzheimer’s. Adding a physical fitness regimen to the lives of those with higher APOE levels, studies have demonstrated, makes their brains healthier and less susceptible to Alzheimer’s than the brains of sedentary people with lower APOE.

Physical activity, Erickson concluded, “trumps genetic risk.”


Still, some scientists disagree on the specific effects of exercise on brain health, he noted, despite a 2015 statement from the Institute of Medicine that physical activity is the most promising factor for improving cardiovascular health.

For one, studies on the effects of physical activity differ in their length and how they measure fitness.

Nor do researchers yet know what happens to hippocampus volume if exercisers simply stop their physical fitness habit — or which variety of exercise works best. “We don’t have very good answers for a lot of these questions right now,” he said.

Erickson hopes some answers will come from a new study for which his lab recently received a five-year, $21.8 million grant from the National Institute on Aging. The study will enroll 639 cognitively normal adults 65-80 and place them into three groups for moderate exercise (brisk walking) at 150 minutes per week, another group of walkers spending 225 minutes per week walking, and a third group stretching and toning for 150 minutes a week.

The aim will be to test whether the correlation between physical activity and brain health is borne out once again.

Even before this latest study, Erickson concluded, “starting to exercise in late life is not futile.” Even those who have been very inactive most of their lives can start exercising “and still see these dramatic effects on the brain.

“We’ve learned a lot about our behaviors and the choices we make,” he added. In fact, research efforts in this area have formed a new field of health neuroscience. “Here in Pittsburgh we feel we are at the heart” of this new field, he said.

—Marty Levine 

Filed under: Feature,Volume 49 Issue 9

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