Study: A 10 years update of effects of exercise on depression disorders—In otherwise healthy adults: A systematic review of meta-analyses and neurobiological mechanisms. Image Credit: People-Images.com / Yuri A / Shutterstock.com

A new PLoS ONE study provides an updated review on how exercise influences depression in otherwise healthy adults.

How does physical activity improve mental health?

The World Health Organization (WHO) considers physical inactivity to be the fourth most important risk factor influencing mortality, in addition to its role in increasing the incidence of many non-communicable diseases. Regular physical activity is strongly associated with positive health outcomes, including improved mental health by reducing the risk of anxiety and cognitive impairment.

Mental health disorders like depression can significantly impact an individual’s quality of life. Although cognitive behavioral therapy (CBT) and pharmacological strategies are frequently prescribed to manage mental health disorders, these strategies are associated with numerous limitations. For example, pharmacological treatment for depression may lead to drug-related side effects, such as constipation, headaches, diarrhea, insomnia, nausea, and drowsiness, whereas CBT is associated with moderate efficacy.

Previously, researchers have reported that over 50% of individuals with depression do not respond to the first line of antidepressants, approximately 30% of whom do not experience any improvements in their symptoms with currently available treatments. Considering the higher global prevalence of depression and low efficacy of available treatments, a cost-effective treatment for depressive disorders is urgently needed.

About the study

In 2014, the researchers of the recent PLoS One study published a meta-analysis revealing that physical exercise had a moderate overall effect size (ES) on depression. Here, the overall ES of physical exercise on depression was 0.56, which is similar to that of pharmacological or psychotherapeutic treatments of depression.

Relevant studies published after 2014 were obtained from PubMed, CINAHL Complete, PsycINFO, Psyndex, SocINDEX, and SPORTDiscus databases for the meta-analysis to update their previous analysis with more recent data.

Eleven studies fulfilled all eligibility criteria and were considered in the final meta-analysis. The study included 229 randomized controlled trials (RCTs), controlled trials, cluster RCTs, and longitudinal studies, comprising 16,255 participants.

Depression levels were measured by the Hamilton Depression Scale (HAM-D), Beck Depression Inventory (BDI), and Hamilton Depression Rating Scale (HAM-D).

Physical activity and exercise as an intervention to manage depression

Over the past ten years, researchers have continuously reported that both exercise and physical activity can reduce depressive symptoms and improve the quality of life of people with depression. These benefits cannot be attributed to a single, isolated mechanism and are likely due to an interplay of multiple both psychological and neurobiological mechanisms.

Although many studies use physical activity and exercise interchangeably, it must be noted that exercise is always physical, but physical activity is not necessarily considered exercise. This is because exercise is more structured and planned, whereas physical activity encompasses anything that causes skeletal muscle contraction and results in a significant increase in caloric expenditure as compared to energy expenditure at rest.

Recent studies have reported that the effect of physical activity/exercise on depressive symptoms varies based on its type, intensity, and minimum duration. As compared to no intervention, exercise can provide a moderate to large impact on alleviating depressive symptoms. Exercise also appears to be more beneficial than usual care, such as placebo pills or waiting list control conditions.

Exercise alleviates depressive symptoms for both men and women. Notably, exercise, psychosocial interventions, and relaxation strategies were found to provide comparable effects. Nevertheless, existing studies emphasize that exercise positively influences patients’ responses to treatment.

In particular, aerobic exercise like swimming, running, jogging, and walking had a stronger antidepressant effect than psychological treatments or antidepressant drugs. Moderate-intensity interventions with a shorter weekly duration provided a more beneficial effect than high-intensity interventions.

Neurobiological explanations and future outlook

Depressive disorders arise due to dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis, reduced responsiveness to glucocorticoids, increased secretion of corticotropin-releasing hormone (CRH), and increased pituitary size and activity. Even ten years after their original meta-analysis, the specific neurobiological changes involved in the anti-depressive effects of exercise and physical activity remain unclear.

Researchers have proposed that the effects of exercise and physical activity may be attributed to physiological changes in hypothalamic-pituitary-adrenal (HPA) axis function, monoamine metabolism, neurotrophic factors, and neuroinflammation. These hypotheses are supported by many systemic reviews that have similarly reported the impact of physical activity on the serotonergic system and HPA axis.

To optimize the antidepressant effects of physical activity, biomarkers of depressive disorders must be monitored regularly. The optimal dose-response relationship must also be determined to provide clinicians with clear guidelines for prescribing this strategy for the treatment of depression symptoms.