Major depressive disorder is linked to an imbalance in levels of cortisol, a hormone involved in the stress response. Beserra et al. (2018) conducted a meta-analysis of 463 studies investigating the connection between exercise and cortisol. They found that exercise leads to a moderate reduction in cortisol. However, discrepancies in methods for measuring cortisol (urine, saliva, plasma) and exercise type or frequency made it difficult to reach a definite conclusion.