Depression affects 5% of adults (4% of men and 6% of women). It is considered the leading cause of disability worldwide and is associated with disruption of a number of brain and psychological processes, including learning and memory problems. Physical activity, especially aerobic exercise, has been found to alleviate depressive symptoms, but the processes involved are not well understood. Now, researchers at University College London (UCL) have explored the processes in the brain and the rest of the body by which physical exercise reduces depressive symptoms.
In a new review article published in Translational Psychiatry, researchers propose a new hypothesis for understanding the antidepressant effects of exercise. In their view, the process may depend on motivation, which is very important for mitigating a number of symptoms of depression, such as anhedonia (loss of interest or indifference to life experiences), lack of energy and ‘brain fog’.
The team of scientists summarized research articles that explored the mechanisms of depression in both humans and animals and concluded that depression – especially anhedonia – is associated with elevated inflammation triggered by the body’s immune response. Importantly, inflammation is also linked to altered dopamine transmission.
These biological changes may represent key processes that lead to changes in motivation, and in particular to a reduced willingness to exert physical or mental effort. Meanwhile, exercise reduces inflammation, increases dopamine function, and improves motivation. Researchers believe this could be an important reason why exercise exerts an antidepressant effect.
Personalized exercise programs to combat depression
Lead author Dr Emily Hird (UCL Institute of Cognitive Neuroscience) said: “The antidepressant effect of aerobic exercise has been convincingly demonstrated across randomised controlled trials, but its mechanism is poorly understood. This is, in part, because it likely involves a range of biological and psychological processes. For example, alongside its positive effect on inflammation, dopamine and reward processing, exercise also reduces oxidative stress and improves self-esteem and self-efficacy.”
“However, we propose that exercise, particularly aerobic activities that make you sweat and leave you breathless, decreases inflammation and increases dopamine transmission, which in turn increases the desire to exert effort and therefore increases overall motivation.”
The team hopes that this understanding of how exercise reduces symptoms of depression will serve as a basis for developing new treatment strategies, such as personalized exercise programs. “Understanding the mechanisms underlying the antidepressant effects of physical activity in depression could also help to understand the mechanisms that cause depression and the development of new intervention strategies, particularly personalized intervention and social prescribing,” Hird said.
“Exercise – particularly aerobic activities – decreases inflammation and increases dopamine transmission, which in turn increases the desire to exert effort and overall motivation.”
To further test their hypothesis, the researchers advise that large randomized controlled trials should be conducted that evaluate the antidepressant effects of exercise while also measuring the effect on variables such as inflammation, dopamine transmission, and motivation. It would also be important to investigate any potential barriers to exercise.
“Addressing barriers to exercise, particularly in people with depression, is crucial, as regular physical activity can alleviate symptoms, improve mood and empower people on their road to recovery. As part of this, finding strategies to encourage exercise is key,” concludes Dr Hird.
