The brain and body processes through which exercise reduces symptoms of depression have been studied by researchers at UCL.
Depression is a leading cause of disability worldwide and is associated with various disturbances in the brain and psychological processes, including learning and memory impairments. Physical activity, particularly aerobic exercise, has been shown to reduce symptoms of depression, but until now the processes behind this have not been well understood.
In a new review article published in the journal Translational Psychiatry, researchers propose a new hypothesis to understand the antidepressant effects of exercise. They believe that the process of exercise depends on motivation, which is crucial for alleviating various symptoms of depression, such as anhedonia (lack of interest or pleasure in life experiences), lack of energy, and brain fog.
The research team summarized research papers that investigated the mechanisms of depression in both humans and animals and concluded that depression, and in particular anhedonia, is associated with increased inflammation (caused by the body’s immune response). Importantly, inflammation is also associated with disruptions to dopamine transmission. These biological changes may be key processes that lead to changes in motivation, especially reduced willingness to exert physical or mental effort.
On the other hand, exercise reduces inflammation, boosts dopamine function, and increases motivation, which researchers believe may be an important reason why exercise exerts an antidepressant effect.
Lead author Dr Emily Hurd (UCL Institute of Cognitive Neuroscience) said: “The antidepressant effects of aerobic exercise have been convincingly demonstrated in randomised controlled trials, but the underlying mechanisms remain poorly understood, in part because they likely involve a range of biological and psychological processes.”
“For example, exercise has a positive effect on inflammation, dopamine and reward processing, as well as reducing oxidative stress and improving self-esteem and self-efficacy.
“However, we argue that exercise, particularly sweaty, breathless aerobic exercise, reduces inflammation and enhances dopamine transmission, thereby increasing the desire to exert effort and therefore generally increasing motivation.”
The research team hopes that understanding how exercise reduces the symptoms of depression may help develop new treatment strategies, such as individualized exercise programs.
Dr Hurd said: “Understanding the mechanisms underlying the antidepressant effects of physical activity in depression may also aid in understanding the mechanisms that cause depression and in the development of new intervention strategies, particularly individualised interventions and social prescribing.”
To further test their hypothesis, the researchers recommend that large randomized controlled trials are needed to evaluate the antidepressant effects of exercise as well as measure its effects on variables such as inflammation, dopamine transmission, and motivation.
It is also important to explore potential barriers to exercise.
Dr Hurd said: “Addressing barriers to exercise is important, particularly for people with depression, as regular physical activity can ease symptoms, boost mood and empower them on the road to recovery. As part of this, finding strategies to encourage movement is key.”
The team are currently conducting a trial based on the hypotheses proposed in the review, which will involve 250 people aged 18 to 60, and is funded by a Wellcome Mental Health Award.
This review article was produced with funding from the Rose Trees Trust.
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