An evaluation of the effects of aerobic exercise interventions on specific biomarkers of mood disorders.
Background Mood disorders, including major depression and bipolar disorder, are as disabling as arthritis, diabetes and cardiovascular disease and are associated with high suicide rates. Although pharmacological treatments are commonly used they present some difficult side effects and 30 to 40% do not respond to them. Aerobic exercise (AE) is a promising adjunct treatment, consistently leading to reduced depression scores. The physiological mechanisms behind this are unclear. Objectives The aim of this study was to evaluate the effects of AE on specific biomarkers of depression whilst also examining the dose-response of these biomarkers. Search strategy Using preselected keywords, the databases Pubmed, Scopus, PsychInfo, Cinahl and Medline were searched to identify relevant articles in April of 2018. Selection criteria The inclusion criteria for the review included those clinically diagnosed with a mood disorder. Eligible studies included those that measured the response of Brain-derived neurotrophic factor (BDNF), Insulin like growth factor-1 (IGF-1), cortisol or inflammatory cytokines to AE. Data collection and analysis The methodological quality of the selected studies was assessed using the Effective Public Health Practice Project (EPHPP) tool. Studies were rated as being strong, moderate or weak quality. Main results Overall twelve studies met the inclusion criteria and were selected for review. One study was deemed as strong methodological quality, two weak and the rest moderate. Eight studies examined the acute response to exercise with all showing significant impacts on BDNF, cortisol or inflammatory cytokines. Four examined longer-term exercise with only one finding significant increases in BDNF. The other three found no influence on IGF-1, Cytokines or cortisol. Conclusions The current systematic review indicates that AE may acutely influence BDNF, Cortisol and Cytokines. The more chronic effects of longer term exercise are unclear with some moderate quality evidence suggesting longer term increases in BDNF. No clear conclusions could be drawn on the dose-response of biomarkers to AE which should be a future area of research.