[It is common for scientific studies to produce apparently
conflicting results, but the benefits of physical activity on a wide
range of physical and mental health outcomes remain undeniable.]
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IS EXERCISE REALLY GOOD FOR THE BRAIN? WHAT THE SCIENCE SAYS
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Matthieu P. Boisgontier and Boris Cheval
May 22, 2023
The Conversation
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_ It is common for scientific studies to produce apparently
conflicting results, but the benefits of physical activity on a wide
range of physical and mental health outcomes remain undeniable. _
hanoi-exercise, by Neil (CC BY-NC 2.0)
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
both brain health and cognition.
A few days after that study was published, our team of health and
neuroscience researchers released the results of our study of over a
quarter million people. Our results clearly support the beneficial
effects of both moderate and vigorous physical activity on cognitive
functioning, fuelling 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 [[link removed]]
was published on March 27, 2023. It is a review of 24 meta-analyses
that re-examines 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 analyses performed were suboptimal. For
example, they point out that both baseline levels of physical activity
and the tendency of the scientific community to publish only
significant results were rarely taken into consideration. Once these
adjustments were made, the authors found results suggesting that the
benefits of exercise are actually smaller than those estimated in the
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 state
that physical activity improves cognitive health, academic
performance, and executive function
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“at least until more reliable scientific evidence accumulates.”
Well, that evidence didn’t take long to arrive.
Genetics and DNA to the rescue
The second study [[link removed]],
ours, is a genetic study involving nearly 350,000 people, published
four days later, on March 31, 2023. Our results provide scientific
evidence for the cognitive benefits of moderate and vigorous physical
activity.
This evidence is based on the two-sample Mendelian randomization
method, which takes advantage of the random variations in our DNA that
occur at conception, before we are even born.
When any two humans are compared, 99.9 per cent of their genetic
material is identical. DNA can be thought of as a long chain of
building bricks, called nucleotides, that varies once every 1,000
bricks between these two humans. There are four types of randomly
arranged bricks: 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 in our study, consisting of 91,084 people, was used
to identify genetic variations associated with differences in physical
activity, as measured by wrist-worn motion sensors
[[link removed]].
The second sample in our study, consisting of 257,854 people, was used
to test whether the 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 more importantly, that the effect of moderate
physical activity (brisk walking, cycling) is 1.5 times greater than
that of vigorous physical activity (running, playing basketball). This
finding highlights that we do not need to push ourselves to the point
of exhaustion to get cognitive benefits from exercise.
[woman on a bike]
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The cognitive benefits of moderate physical activity are 1.5 times
greater than those of vigorous physical activity. (Shutterstock)
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 achieving at least moderate intensities to reap the
cognitive benefits of physical activity.
Our results are consistent with those of a recent study
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that emphasizes 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 feed 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 function. The very existence
of this explanatory mechanism
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strengthens the results supporting a beneficial effect of exercise on
brain functioning.
It’s never too late to get started
Several differences may explain the discrepancy in results between the
review of meta-analyses and our genetics-based study.
First, the review looks only at healthy people, which is not the case
in our study. Second, our study distinguishes between light, moderate,
and vigorous physical activity, whereas the review does not make this
distinction. Finally, our genetic approach evaluates long-term
effects, over a lifetime, whereas the review is based on interventions
lasting between one month and two years.
As we are dealing with the temporal aspects of physical activity here,
it is important to remember that it is never too late to start
exercising. In fact, a 2019 study
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showed that starting to be active late in life has the same overall
positive health effects as being active throughout life.
Conclusion: Hasty decisions are never good
Based on our findings, it appears that physical activity can still be
considered beneficial for brain health and cognition. Moreover, in the
current socio-political climate of mistrust of science, we should not
jump to conclusions on the basis of a single study that contradicts
years of research, yet is based on the very 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
changing public health messages. As this article shows, we are nowhere
near that point, and the benefits of physical activity on a wide range
of physical and mental health outcomes remain undeniable.[The
Conversation]
Matthieu P. Boisgontier
[[link removed]],
Associate Professor, Faculty of Health Sciences, _L’Université
d’Ottawa/University of Ottawa
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and Boris Cheval
[[link removed]], Senior
Researcher, Swiss Center for Affective Sciences, _Université de
Genève
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This article is republished from The Conversation
[[link removed]] under a Creative Commons license. Read
the original article
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