Exercise makes the brain younger, and scientists can’t explain why

A year of consistent exercise appears to rejuvenate brain activity, but don’t ask scientists how yet

Sticking to an exercise regimen isn’t easy, but a younger mind is a powerful motivator. When researchers asked middle-aged adults to exercise regularly for a year, their brains became noticeably “younger,” so to speak.

After 12 months of regular training, the participants’ brains appeared about seven months younger than when they started. MRI scans analyzed by machine learning algorithms showed measurable structural changes associated with younger brains.

Scientists have examined many possible explanations for why this happens, and none have been successful. Fitness improved. My blood pressure didn’t budge. The weight remained the same. Brain growth factors did not show obvious changes. None of these factors was responsible for the shift in brain age.

“The pathways through which these effects occur remain unknown,” researchers from the University of Pittsburgh and the Advent Health Research Institute wrote in the journal. Journal of Sports and Health Sciences.

The study followed 130 adults between the ages of 26 and 58, none of whom were particularly active to begin with. Half were assigned to an exercise program, and the other half to a control group that had just received general health information. The exercise group committed to 150 minutes of moderate aerobic activity per week, the same recommendation countless doctors give their patients. Two sessions were performed weekly in a supervised university laboratory, and the remainder at home (walking, jogging, treadmill, bicycle, elliptical, etc.).

What does brain age actually measure?

To better understand “brain age,” researchers fed thousands of MRI scans into a computer, teaching it what a typical 30-year-old brain looks like versus a typical 50-year-old brain. Patterns include brain size, structure, and other subtle neurological features.

When someone has their brain scanned, a computer predicts their age based solely on what it sees. If you’re 45 but your brain looks more like the brain of an average 48-year-old, you’re aging faster than average. If your brain looks 42, you’re aging more slowly.

In other studies, each additional year on the brain aging scale has been linked to about a 3% increased risk of developing dementia in the future. People whose brains look older than their age tend to die early and show sooner cognitive decline. Your brain age in midlife may predict your mental acuity in your 70s and 80s.

A fitness connection no one can explain

Before starting the study, the researchers found something in the basic measurements. People who were fitter had younger-looking brains. For every significant bump in measured cardiac fitness, the brain age appeared nearly two years younger on average.

So, when the exercise group became fitter over the course of the year (which they measurably did), the researchers speculated that this would explain everything. It didn’t happen. Yes, fitness has improved. Yes, brain age has decreased. However, statistical analysis showed that the improvement in physical fitness did not take into account brain changes.

Body composition? No change in either group. blood pressure? Same story. BDNF, a protein often associated with brain health, did not show a clear and meaningful increase in exercisers, and did not explain the brain age changes anyway.

The researchers identified the usual suspects that they measured. Nothing added.

“This was a surprise,” lead author Dr. Lu Wan, a data scientist at the AdventHealth Research Institute, said in a statement. “We expected an improvement in physical fitness or blood pressure to explain the effect, but they did not. Exercise may work through additional mechanisms that we have not yet identified, such as subtle changes in brain structure, inflammation, vascular health or other molecular factors.”

What could happen (besides what was measured)

Of course, the brain does not exist in isolation. Exercise triggers a series of changes throughout the body, and researchers have measured only a few possibilities.

Perhaps exercise changes inflammatory signals in ways that the study was unable to capture. This may have improved blood flow to the brain through mechanisms not apparent in simple blood pressure readings. Mitochondria, the tiny power plants in cells, may have become more efficient. It is possible that metabolic changes occurred and were not tracked.

Instead, brains may have responded to exercise along pathways that science has not yet fully mapped out. The study was not designed to measure all possible mechanisms, but only the most obvious candidates.

What researchers do know is that 150 minutes of weekly exercise (two and a half hours, divided as desired) was enough to produce measurable changes in brain structure within a year.

Why are your 30s, 40s and 50s important?

Most studies of brain aging focus on people in their 70s and 80s, after cognitive decline has already begun. This study intentionally targeted younger adults because middle age appears to be a focal point.

Risk factors that appear in your 40s (high blood pressure, obesity, inactivity) predict your risk of developing dementia 20 or 30 years later. But midlife is also a time when intervention may be most important. Your brain is still flexible enough to respond, but the aging processes have begun.

The participants in this study were not elderly, were not ill, and did not already have cognitive problems. They were ordinary people, two-thirds of whom were women, and their average age was 41 years. Most were sedentary, doing less than 100 minutes of exercise per week before the study began. In other words, they looked a lot like American adults.

Their brains at the start of the study were aging normally on average, although individual participants varied slightly. Twelve months of exercise changed this course.

An exercise program that worked

Nothing in the exercise regimen requires a gym membership or special equipment. Participants walked, jogged, or used any cardio equipment they had access to. Heart rate monitors made sure they worked hard enough, breathing hard but still able to talk, and working at about 60-75% of their maximum heart rate.

The group stuck with it remarkably well. They completed 93% of their assigned exercise minutes. Attendance at the lab was 73%, and people made up the difference at home.

Meanwhile, the control group’s fitness declined slightly over the course of the year, as happens when sedentary people remain sedentary. Their brain age drifted slightly upward on average.

The pandemic has also complicated matters. Some participants were unable to complete final assessments, and for several months in 2020, lab sessions came to a complete halt. However, 89% of the exercise group returned once facilities reopened, and results remained consistent.

What does this mean for your brain?

Previous studies have shown that brain age can be turned back through extreme interventions: intensive diet and exercise programs in people with obesity, or bariatric surgery. This study extends to healthy middle-aged adults who engage in moderate exercise.

The practical idea is straightforward: It seems that the exercise recommendation you’ve heard a thousand times (150 minutes of moderate activity per week) is enough to change the course of aging in your brain. No need to run marathons or spend long hours in the gym.

But in the end, the scientific mystery remains. Exercise has changed brain structure in ways that make the brains of 40-year-olds look younger, and researchers still can’t pinpoint the mechanism. This is not a weakness of the study. It’s a reminder of how little we understand the relationship between physical movement and the brain.

Future research will need to dig deeper, measure more pathways, track more biomarkers, and follow people for longer periods. For now, we’re left with a “what” question without a “why”: Exercise appears to slow or reverse brain aging, even when the usual suspects don’t explain it.

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Disclaimer: This article is for informational purposes only and is not intended to provide medical advice. The study looked at healthy adults between the ages of 26 and 58 under supervised conditions. Before starting any new exercise program, consult your healthcare provider, especially if you have existing health conditions, are inactive, or are taking medications. Individual results may vary, and the mechanisms by which exercise affects brain structure are not fully understood.

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