Exercise -> serotonin -> antidepressant
It’s well-established that exercise can be a powerful tool against depression (as Gretchen Reynolds wrote about in the New York Times a few months ago). What’s less clear is how and why it might help. A new study in Medicine & Science in Sports & Exercise, from researchers at the University of Sherbrooke, offers some evidence for the theory that exercise can boost serotonin levels in the brain. This, of course, is pretty much the same as what the most common antidepressants (SSRIs: selective serotonin reuptake inhibitors) do.
The study was pretty straightforward. They had 19 men with an average age of 64 perform a 60-minute bout of exercise at moderate intensity (average HR 129 beats per minute, 68% VO2max). Then they measured several proxies of serotonin production, since it’s very difficult to directly measure neurotransmitters in the brain. The result: levels of tryptophan — the key precursor which is converted into serotonin — roughly doubled.
Is this a surprise? There was previous evidence in studies of rodents and younger humans that exercise boosted tryptophan availability, but it wasn’t clear whether the same effect would occur in older adults. This is particularly important because we become increasingly susceptible to depression as we age, suggesting that some of the mechanisms that help us ward off depression stop working quite as well.
Of course, one of the problems with “prescribing” exercise as a depression treatment (as Reynolds notes) is that once you’re depressed, it can be extremely difficult to summon the motivation needed to maintain a regular exercise program. Still, this study suggests that exercise might help to prevent depression in the first place, particularly as you get older.