UCL researchers have investigated the brain and body systems that alleviate depressed symptoms through physical activity. Depression is the biggest cause of disability worldwide, and it has been linked to disruptions in a variety of brain and psychological functions, including decreased learning and memory. Physical activity, particularly aerobic exercise, has been shown to lessen depressive symptoms, but the mechanisms underlying this have been poorly understood.
In a new review article published in Translational Psychiatry, researchers present a novel hypothesis for understanding exercise’s antidepressant benefits. They believe that the process is dependent on motivation, which is critical for treating a variety of depressive symptoms, including anhedonia (a lack of interest or joy in life’s experiences), low energy, and ‘brain fog’.
The researchers evaluated research publications on the processes of depression in both humans and animals and concluded that depression, particularly anhedonia, is connected with increased inflammation (produced by the immune system). Importantly, inflammation has been associated to impaired dopamine transmission. These biochemical changes may be crucial factors that lead to changes in motivation, specifically a decreased willingness to expend physical or mental effort.
Addressing barriers to exercise – particularly in people with depression – is crucial, as regular physical activity may be able to alleviate symptoms, enhance mood and empower individuals on their path to recovery. As part of this, finding strategies to encourage exercise is key.
Dr Emily Hird
Meanwhile, exercise lowers inflammation, increases dopamine function, and stimulates motivation. The researchers feel that this could be a key reason why exercise has an antidepressant impact.
The lead author, Dr Emily Hird (UCL Institute of Cognitive Neuroscience), stated, “The antidepressant effect of aerobic exercise has been convincingly demonstrated through randomised controlled trials, but its mechanism is not well understood.” This is due in part to the fact that it is most likely a combination 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 are proposing that exercise — particularly aerobic activities that make you sweaty and out of breath — decreases inflammation and boosts dopamine transmission, which in turn increases the desire to exert effort, and therefore boosts motivation generally.”
The team hope that this understanding of how exercise reduces symptoms of depression will help to inform the development of new treatment strategies – such as personalised exercise programmes.
Dr Hird said: “Understanding the mechanisms that underly the antidepressant effects of physical activity in depression could also inform our understanding of the mechanisms causing depression and the development of novel intervention strategies, in particular personalised intervention, and social prescribing.”
To further test their hypothesis, the researchers advise that large randomised controlled trials need to be conducted that assess the antidepressant effects of exercise, whilst also measuring the effect on variables including inflammation, dopamine transmission and motivation. It would also be important to investigate any potential barriers to exercise.
Dr Hird said: “Addressing barriers to exercise — particularly in people with depression — is crucial, as regular physical activity may be able to alleviate symptoms, enhance mood and empower individuals on their path to recovery. As part of this, finding strategies to encourage exercise is key.”
The team are now running a trial based on the hypothesis proposed in the review, which will involve 250 participants aged 18 to 60 and is funded by a Wellcome Mental Health Award.
