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Advertisements for cortisol blockers as weight-loss treatment are in vogue right now, but the efficacy of such supplements is suspect. For one thing, your body needs a certain level of cortisol for proper function, so it isn't a great idea to go blocking them all willy-nilly. By the same token, you definitely don't want too many corticosteroids floating around in your body. Historically, stress was induced by starvation, so the function of corticosteroids is to prepare the body to go without food for a while. Corticosteroids increase glucose utilization and promote the breakdown of fat, protein, and eventually bone. The energy liberated by this process is stored as fat near the vital organs, hence why the cortisol blocker commercials target people with 'belly fat'. In the present day, stress can be caused by a plethora of things other than starvation, but the body's response to stress remains the same. In addition to breaking down the body's resources to liberate energy, corticosteroids also temporarily block growth and development all over the body, including neurogenesis and proper brain function, which can manifest as elevated anxiety.
But back to exercise. As I said above, despite causing elevated levels of corticosteroids, physical activity results in an increase in mental health and brain function for most people. This phenomenon has recently been linked to the idea that exercise is mentally linked to personal reward. As Leuner and colleagues put it in their paper, Sexual Experience Promotes Adult Neurogenesis in the Hippocampus Despite an Initial Elevation in Stress Hormones, "[A] recent study showed that rewarding intracranial self-stimulation is sufficient to increase adult neurogenesis, suggesting that the hedonic aspect of physical exercise may be responsible for its beneficial effects on structural plasticity," (see article for citation). The authors decided to test this pleasure/reward hypothesis by seeing what effect sexual activity has on corticosteroid levels and anxiety.
"Adult male rats were exposed to a sexually-receptive female once (acute) or once daily for 14 consecutive days (chronic) and levels of circulating glucocorticoids were measured." The rats were also measured for neurogenesis and dendritic complexity in the hippocampus. "Finally, to evaluate whether sexual experience alters hippocampal function, rats were tested on two tests of anxiety-like behavior: novelty suppressed feeding and the elevated plus maze."
As you can see in the image above, rats that were briefly exposed to sexually receptive females experienced an increase in corticosteroid levels compared to a control, but also experienced increased neurogenesis (that's what that stuff on the right Y-axis means) compared to a control.
However, rats that were allowed access to a sexually receptive female for two weeks did not experience an increase in corticosteroid levels, but still experienced increased neurogenesis compared to a control.
When tested for anxiety, both sexually active and control rats had similar performances on the maze, but sexually active rats were quicker to feed in an unfamiliar setting than control rats. This was not due to a difference in appetite, since both sets of rats performed similarly when fed in their familiar cages.
It is clear that sex and exercise have similar positive effects on the brain despite increasing corticosteroid levels. Both of these activities have been shown to be rewarding in rodent models (but, really, just consider how you feel after taking a run or having sex), suggesting that the harmful effects of physically stressful behaviors may be overridden if the behavior itself evokes pleasure in the individual.
This possibility raises questions about what factors associated with reward might participate in protecting the brain from the negative influence of stress hormones and further, whether similar or other factors are responsible for the beneficial effects of sexual experience. In this regard, a role for neuromodulators altered with sexual experience and known to influence adult neurogenesis, like opiates or dopamine, seem plausible, as does oxytocin, a neuropeptide that buffers the brain and body against some of the adverse consequences of stress hormones.
Not only did sex result in increased neurogenesis and decreased anxiety, but recurring sexual activity brought sex-induced corticosteroid levels back down to the level of control over time. So, sex gets less stressful the more you have it? Okay, sign me up!
Leuner, B., Glasper, E., & Gould, E. (2010). Sexual Experience Promotes Adult Neurogenesis in the Hippocampus Despite an Initial Elevation in Stress Hormones PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011597