Evaluation of the benefits of exercise on cognition in major depressive disorder

Background: Cognitive impairment is increasingly recognized as a significant symptom in patients with major depressive disorder (MDD). While exercise is already recommended in many treatment guidelines for patients with MDD and has been shown to improve cognition in other disorders (e.g., Alzheimer's, Parkinson's, schizophrenia), limited research is available evaluating the effect of exercise on cognition in MDD. Methods: We provide a narrative review of existing literature regarding the effect(s) of exercise on cognition across several neurodegenerative and psychiatric diseases, and particularly in MDD, with specific emphasis on study design and methodology that may impair adequate synthesis of the results. We also describe mechanisms by which exercise may improve cognition in depression and other brain disorders. Results: Of existing studies with MDD, data are equivocal, as some are supportive of improved cognition, whereas others demonstrate no benefit. Several limitations were noted, including insufficiently-powered designs, variability in interventions examined (e.g., aerobic, anaerobic, mind-body) or control groups, lack of attention to the status of baseline cognitive impairment, and/or heterogeneity across outcome measures and clinical characteristics. Conclusions: While preliminary results suggest the potential for exercise as a beneficial treatment or augmentation strategy for impaired cognition in MDD, the aforementioned limitations necessitate further investigation.