The health benefits of physical activity are undeniable.
Yet a recent study based on data published over the past 30 years challenges the famous adage Mens sana in corpore sano (a healthy mind in a healthy body) and questions the importance of exercise for brain health and cognition.
A few days after the publication of this study, our team of health and neuroscience researchers published the results of our study involving more than a quarter of a million people. Our results clearly confirm the beneficial effects of moderate and vigorous physical activity on cognitive functioning, fueling an important scientific debate.
Who is right and who is wrong? Here’s what the science says.
Is physical exercise useless for cognitive functioning?
THE first study was published on March 27, 2023. This is a review of 24 meta-analyses that reexamines data from 11,266 healthy people using a more rigorous approach.
Although almost all of the 24 meta-analyses included in this review concluded that exercise had a positive effect on cognitive function, the authors argue that the analyzes performed were suboptimal. For example, they point out that baseline physical activity levels and the tendency of the scientific community to publish only meaningful results have rarely been taken into consideration. After making these adjustments, the authors found results suggesting that the benefits of exercise are actually lower than those estimated in previous meta-analyses, and may even be negligible.
Based on these findings, the authors argue that public health agencies such as the World Health Organization (WHO) should no longer report that physical activity improves cognitive health, academic performance and executive function“at least until more reliable scientific evidence accumulates.”
Well, that proof didn’t take long to arrive.
Genetics and DNA to the rescue
THE second studyours, is a genetic study of nearly 350,000 people, published four days later, March 31, 2023. Our results provide scientific evidence for the cognitive benefits of moderate and vigorous physical activity.
This evidence is based on the Mendelian two-sample randomization method, which takes advantage of the random variations in our DNA that occur at conception, even before we are born.
When two humans are compared, 99.9% of their genetic material is identical. DNA can be thought of as a long string of building blocks, called nucleotides, that vary once every 1,000 building blocks between these two humans. There are four types of bricks arranged randomly: thymine, adenine, guanine and cytosine. Genetic variations can result in, for example, a cytosine brick in one place in one person’s DNA and a thymine brick in the same place in another.
The first sample of our study, consisting of 91,084 people, was used to identify genetic variations associated with differences in physical activity, measured by motion sensors worn on the wrist.
The second sample of our study, consisting of 257,854 people, was used to test whether genetic variations associated with physical activity had a proportional effect on cognitive functioning. Since this was the case, we were able to conclude that there is a causal effect of physical activity on cognitive function.
Moderate exercise goes a long way
In our study, we show that physical activity improves cognitive functioning, but above all that the effect of moderate physical activity (brisk walking, cycling) is 1.5 times greater than that of vigorous physical activity (running walking, basketball). This finding underscores that we don’t need to push ourselves to exhaustion to get cognitive benefits from exercise.
When all types of physical activity were considered together (including sedentary and light physical activity), our results no longer showed an effect on cognitive function. This finding confirms the importance of reaching at least moderate intensities to reap the cognitive benefits of physical activity.
Our results are consistent with those of a recent study which highlights the importance of exercise duration and intensity for the release of a protein called BDNF in the brain. This protein is involved in the creation of new neurons, new connections between these neurons, and new blood vessels to supply them.
This protein, whose production increases during exercise, is therefore one of the physiological mechanisms that explains the beneficial effects of physical activity on cognitive functions. The very existence of this explanatory mechanism further reinforces findings supporting a beneficial effect of exercise on brain function.
It’s never too late to start
Several differences may explain the discrepancy in results between the review of meta-analyses and our genetics-based study.
First, the review only looks at healthy people, which is not the case in our study. Second, our study distinguishes between light, moderate and vigorous physical activities, whereas the review does not make this distinction. Finally, our genetic approach assesses long-term, lifespan effects, whereas the review is based on interventions lasting between one month and two years.
As we are dealing here with the temporal aspects of physical activity, it is important to remember that it is never too late to start exercising. In fact, a 2019 study showed that starting to be active later in life has the same overall positive health effects as being active throughout life.
Conclusion: hasty decisions are never good
Based on our results, it appears that physical activity can still be considered beneficial for brain health and cognition. Moreover, in the current socio-political climate of distrust of science, we should not jump to conclusions based on a single study that contradicts years of research, but is based on the same data.
As is often the case in science, it is wiser not to make hasty decisions but to wait for additional studies before suggesting changes to physical activity guidelines. The accumulation of converging evidence from different research teams should be a prerequisite for the evolution of public health messages. As this article shows, we are far from there and the benefits of physical activity on a wide range of physical and mental health outcomes remain undeniable.
