Exercise and Depression
Moderate to vigorous exercise is generally accepted as an effective treatment for depression. In this post we will explore some of the reasons why this may be the case.
The Tryptophan Pathway
Tryptophan, the amino acid in turkey thought to make you sleepy, is a precursor to the neurotransmitter Serotonin. Serotonin is well-known for contributing to feelings of well-being, and boosted in the brain by a class of anti-depression drugs known as SSRIs (Selective Serotonin Reuptake Inhibitors). Tryptophan, however, instead of participating in your brain’s creation of serotonin, can instead convert to something called kynurenine. The accumulation of kynurenine is associated with depression, possibly because it’s a precursor to the neurotoxic quinolinic acid, though it can also become the neuroprotective kynurenic acid. One key to curing or preventing depression seems to be maximizing the amount of tryptophan that gets converted into serotonin and kynurenic acid and minimizing the amount that becomes quinolinic acid. Exercise is believed to promote the production of serotonin and kynurenic acid while chronic inflammation and stress is thought to contribute to excess kynurenine and quinolinic acid.
Exercise and Neuroplasticity
Another correlate of depression, lack of neuroplasticity, or the relative inability of the brain to rearrange neural pathways, remove neural connections, and grow new cells appears to be mitigated by exercise through a couple of different mechanisms. During exercise the cytokine IL-6 (a type of cell signaling protein) is released. This release of IL-6 is thought to play an important role in fat metabolism as well as in facilitating neuroplasticity. Another key contributor to neuroplasticity, Brain-Derived Neurotrophic Growth Factor (BDNF), is released during vigorous aerobic activity. Additionally, decreased levels of BDNF are associated with depression.
While most of the above applies to aerobic exercise, resistance training has similarly been shown to improve symptoms of depression, so there’s no need to overthink things. Find an exercise you enjoy doing, and force yourself to do it at least every other day. If you’re having trouble sticking to it, find a friend with similar ambitions and hold each other accountable. For more on this topic see the fantastic Youtube video by Rhonda Patrick of FoundMyFitness.