Exercise
may be an effective treatment for depression and might even help
prevent us from becoming depressed in the first place, according to
three timely new studies.
The studies pool outcomes from past research
involving more than a million men and women and, taken together,
strongly suggest that regular exercise alters our bodies and brains in
ways that make us resistant to despair.
Scientists
have long questioned whether and how physical activity affects mental
health. While we know that exercise alters the body, how physical
activity affects moods and emotions is less well understood.
Past
studies have sometimes muddied rather than clarified the body and mind
connections. Some randomized controlled trials have found that exercise
programs, often involving walking, ease symptoms in people with major
depression.
But
many of these studies have been relatively small in scale or had other
scientific deficiencies. A major 2013 review of studies related to
exercise and depression concluded that, based on the evidence then
available, it was impossible to say whether exercise improved the
condition. Other past reviews similarly have questioned whether the
evidence was strong enough to say that exercise could stave off
depression.
A
group of global public-health researchers, however, suspected that
newer studies and a more rigorous review of the statistical evidence
might bolster the case for exercise as a treatment of and block against
depression.
So for the new analyses, they first gathered all of the most recent and best-designed studies about depression and exercise.
Then, for perhaps the most innovative of the new studies, which was published last month in Preventive Medicine, they focused on whether exercise could help to prevent someone from developing depression.
The
scientists knew that many past studies of that topic had relied on
people providing reports about how much they had exercised. We human
beings tend to be notoriously unreliable in our memories of past
workouts, though.
So
the researchers decided to use only past studies that had objectively
measured participants’ aerobic fitness, which will rise or fall
depending on whether and how much someone exercises. Participants’
mental health also had to have been determined with standard testing at
the start and finish of the studies, and the follow-up time needed to
have been at least a year and preferably longer.
Ultimately,
the researchers found several large-scale past studies that met their
criteria. Together, they contained data on more than 1,140,000 adult men
and women.
Among
these million-plus people, the links between fitness and mental health
turned out to be considerable. When the researchers divided the group
into thirds, based on how aerobically fit they were, those men and women
with the lowest fitness were about 75 percent more likely to have been
given diagnoses of depression than the people with the greatest fitness.
The men and women in the middle third were almost 25 percent more
likely to develop depression than those who were the most fit.
In
a separate study (some of the scientists were involved in each of the
reviews), researchers looked at whether exercise might be useful as a
treatment for depression. In that analysis, which was published in June in the Journal of Psychiatric Research,
they pooled data from 25 past studies in which people with clinically
diagnosed depression began some type of exercise program. Each study had
to include a control group that did not exercise and be otherwise
methodologically sophisticated.
The
pooled results persuasively showed that exercise, especially if it is
moderately strenuous, such as brisk walking or jogging, and supervised,
so that people complete the entire program, has a “large and significant
effect” against depression, the authors wrote. People’s mental health
tended to demonstrably improve if they were physically active.
The final review offers some hints about why. Published in February
in Neuroscience and Biobehavioral Reviews, it took on the difficult
issue of what happens within our bodies during and after exercise that
might affect and improve our moods. The researchers analyzed 20 past
studies in which scientists had obtained blood samples from people with
major depression before and after they had exercised. The samples on the
whole indicated that exercise significantly reduced various markers of
inflammation and increased levels of a number of different hormones and
other biochemicals that are thought to contribute to brain health.
But
the researchers also caution that most of the physiological studies
they reviewed were too small and short-term to allow for firm
conclusions about how exercise might change the brain to help fight off
gloom.
Still,
the three reviews together make a sturdy case for exercise as a means
to bolster mental as well as physical health, said Felipe Barreto
Schuch, an exercise scientist at the Centro Universitário La Salle in
Canoas, Brazil, who, with Brendon Stubbs, a professor at King’s College
in London, was a primary author on all of the reviews.
Many
more experiments are still needed to determine the ideal amounts and
types of exercise that might help both to prevent and treat depression,
Dr. Schuch said.
But
he encouraged anyone feeling overwhelmed by recent events, or just by
life, to go for a run or a bike ride. “The main message” of his and his
colleagues’ reviews, he said, “is that people need to be active to
improve their mental health.”
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