It’s never too late for exercise to boost your brain health

Nov 18, 2023

Exercise can sharpen your thinking and keep your brain healthy as you age — even if you don't start exercising until later in life.

That's the finding of a new study that found that previously sedentary 70- and 80-year-olds who started exercising, including some who had already experienced some cognitive decline, showed improvement in their brain function after workouts.

The study adds to mounting evidence that one of the best ways to protect our minds may be to move our bodies.

"Exercise does seem to be key" to maintaining and even improving our ability to think as we age, said J. Carson Smith, a professor of kinesiology at the University of Maryland at College Park, who led the study.

As many of us know from doleful experience, mental agility often stutters as we grow older, beginning in early middle age and accelerating from there. We have increasing trouble remembering names or where we parked the car or whether we took a vitamin this morning or was that yesterday?

Brain scans and other research suggest this decline occurs in part because the brain's structure and function can fray over time. Neurons weaken or die and the connections between individual neurons, as well as between broader networks of cells within the brain, wither.

Scientists naturally have wondered if we can slow or reverse this falloff in our brains’ function. To investigate that pressing question, Smith and his colleagues recruited 33 volunteers in their 70s and 80s, about half of whom were experiencing mild cognitive impairment, a loss of thinking skills that often precedes Alzheimer's disease.

Everyone was asked to complete an array of physiological and mental tests. In one, the researchers read aloud a brief story and asked the volunteers to recount it. In another, the volunteers lay quietly during a functional MRI scan that pinpointed electrical activity in many parts of their brains.

Afterward, half of the volunteers, including some with mild cognitive impairment, started exercising, visiting a supervised gym four times a week to briskly walk for about 30 minutes. The others stayed inactive.

After four months, everyone repeated the original tests.

But their results diverged. The exercisers, even those with mild cognitive impairment, scored better on the cognitive tests, particularly the repeat-the-story version. The sedentary volunteers didn't.

More intriguing, the exercisers’ brains had changed. Before the study, brain scans of the older volunteers had showed mostly weak or scattershot connections between and within major brain networks.

Our brains work best when various, distinct networks interact and connect, facilitating complex thinking and memory formation. This process can be seen in action on brain scans, when connected brain networks light up in tandem, like synchronized Christmas lights.

After four months of exercise, the scans showed that brain connections were stronger than before, with cells and whole networks lighting up at the same time, a common hallmark of better thinking.

To better understand precisely how exercise may change our brains as we age, though, neuroscientists have needed to turn to mice.

Researchers have known for some time that mammalian brains, including ours, create some new neurons in adulthood, a process called neurogenesis.

Neurogenesis is important for brain health and happens to be amplified by exercise. In studies, when mice run, they pump out double or triple as many new neurons as sedentary animals.

But those neurons aren't beneficial if they don't survive and integrate into the broader brain networks. In a study, which was published in May in eNeuro, researchers let one group of young-adult mice run, while others stayed still, and then injected all of the animals’ brains with a safe, modified virus, made to infect newborn neurons and mark them with a phosphorescent dye from jellyfish.

Then, for six months, the runners ran and the sitters sat, after which the researchers added a different substance to the mouse brains, designed to glom onto the glowing cells — the ones created when the animals were young and first started running or not — and work its way into their wiring, the snaking dendrites that connect neurons to each other and to farther flung parts of the brain.

Using the substance as a marker, the researchers could trace each of these cells’ connections.

And they found that the exercising mice not only had created more neurons when they first took up running than the sedentary animals, but now, as the mice neared retirement age (in rodent terms), those same cells were wired more intricately and extensively into the animals’ brain networks.

The runners’ neurons were better connected than the neurons of sedentary animals.

What does this research mean for the rest of us, who may not yet be elderly or mice?

"I think it should be encouraging," especially for people who may be worried that their brain is starting to dull, Smith said. In his study, even once-sedentary older people with signs of worrisome cognitive decline improved their brain's connections and thinking with just a few hours of walking a week.

But the findings also suggest starting to exercise while you’re young may be even wiser. The young mice that ran probably built up a "cognitive reserve" of healthy neurons and connections, more than among the inactive animals, that served them well as they aged, said Henriette van Praag, an associate professor of biomedical science at Florida Atlantic University and senior author of the mouse study.

Better yet, start and don't stop.

"Given the state of the science, I’d say it's probably a good idea to pursue physical activity during youth, and continue during middle and even older age," said Russell Swerdlow, a professor of neurology and director of the University of Kansas Alzheimer's Disease Research Center, who was not involved with the new studies.

Do you have a fitness question? Email [email protected] and we may answer your question in a future column.

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