There are many possible causes of depression. Some have biological
explanations (or, at least, speculations) — genetic vulnerability,
medications, chemicals in the brain. Others are personal and
psychological: Stressful life events such as illness, divorce, a death,
unemployment. (Personally, I would add, there’s also the philosophical
despair that follows exposure to inequality, injustice, violence,
suffering, and misogyny.) It’s much easier for biomedicine to study the
biological causes rather than the psychological (or philosophical) ones.
Physical exercise is often recommended as a way to alleviate
depression and to alter our mood. Biomedicine would like to know if
exercise really does change the chemicals in our brain. A recent article
in
NEJM reports on a study that suggests it does:
Muscling In on Depression.
The
explanation is rather technical but here’s my summary in a nutshell.
Tryptophan, an essential amino acid in the human diet, is found in foods
containing protein (it’s also in chocolate). When we experience stress,
organs such as the liver produce enzymes that cause tryptophan to
produce. In order to metabolize tryptophane, our bodies produce
kynurenine. Sometimes quite large amounts are produced, and that's not
good. Kynurenine is associated with depression, cognitive deficits of
schizophrenia, Alzheimer’s, and tics. Exercise produces an enzyme that
converts kynurenine to kynurenic acid, which is much better than having kynurenine floating around, wreaking havoc and causing depression.
Admirable,
no doubt, but do I detect here the possibility that the pharmaceutical
industry may soon be at work on a pill it can market as an alternative
to exercise? Possibly. But in the meantime, exercise! It really does
help with depression both physically and psychologically.
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