Do sleep problems, fatigue and physical inactivity lead to a depressed mood, or is it the other way around? The answer seems to be that it goes both ways: depression can lead to inactivity, or inactivity can lead to depression.
Please recall that depression is now viewed as an inflammatory disorder.
So if exercise calms depression, does that mean that exercise is an anti-inflammatory? Well, it appears that may be the case, sort of. Exercise causes the release of chemicals called myokines, cytokines and chemokines. Some of these are inflammatory, but that is needed to start the repair and building process after exercise. And some are anti-inflammatory, yet the overall net effect is anti-inflammatory. One reason is that exercise causes the release of Growth Hormone and Brain Derived Neurotrophic Factor (BDNF). Both of these improve brain function, growth and development.
There are most likely many things that exercise does that decrease inflammation and improve depression. This can be the calming of the sympathetic system, the reduction of cortisol, balancing blood sugar, reducing insulin resistance, improving blood flow and oxygenation to the brain, normalization of hormones, assistance to mitochondria, improved sleep and more.
Bottom Line: If you are having issues with depression, it is important to consider exercise as one of your treatments. Along with reducing inflammation from all possible causes, and the use of therapy, prayer, medications, meditation, stress reduction, clean food, supplements as part of a comprehensive approach to brain health, make sure you add exercise. Contact a personal trainer to make sure you get started right or to upgrade or refresh your exercise plan.