There's little debate that exercise is good for you. An abundance of scientific data demonstrates that regular moderate- to vigorous-intensity aerobic activity – whether it's running, cycling, kickboxing, or shimmying across the dance floor – can help prevent weight gain, improve cardiovascular and metabolic health, and reduce the risk of developing cancer. But for many people who exercise regularly, the benefits are more tangible: It simply makes them feel good. In fact, the feel-good effects of exercise may be one of the most powerful strategies available to improve a person's mental health, whether they're suffering from a mild case of mental funk or dealing with anxiety or major depressive symptoms. Read more about depression and get a broader overview on our topic page.
In this episode, Dr. Rhonda Patrick talks about her love of cycling for its powerful mood-enhancing effects and describes the compelling science that suggests exercise is a powerful tool for preventing or managing the symptoms of depression and mental illness.
The case for attributing causality to the role of exercise in improving mood and preventing or managing the symptoms of depression is bolstered by multiple types of converging evidence. For example, Mendelian randomization studies, which provide evidence of links between modifiable risk factors and disease based on genetic variants within a population, have found that not only are some people genetically predisposed to engage in more physical activity, but they are also less likely to suffer from depression. Randomized controlled trials have also demonstrated that exercise may be an effective intervention for preventing or mitigating depression, especially as an adjunct treatment. Perhaps some of the most interesting findings come from mechanistic studies, which have identified the molecular mechanisms that drive the improvements in mood that accompany exercise.
Many of these mechanistic studies point to the mood-enhancing activities of a few molecules: kynurenine, a compound produced during the conversion of the amino acid tryptophan to the vitamin niacin; brain-derived neurotrophic factor, or BDNF, a type of neurotrophin – or growth factor – that controls and promotes the growth of new neurons; as well as components of the body's opioid and endocannabinoid systems, which play roles in pain control and mood regulation.
Exercise, particularly endurance or high-intensity aerobic exercise, may impact kynurenine metabolism in a way that is beneficial for creating resilience against stress-induced depression.
Kynurenine is pivotal to the tryptophan metabolism pathway because it can be converted into the neuroprotective agent kynurenic acid or to the neurotoxic agent quinolinic acid, the latter of which has been implicated in many disorders, including depression. Exercising muscles, however, take up kynurenine, preventing its conversion to quinolinic acid.
BDNF is active in the hippocampus, cortex, cerebellum, and basal forebrain – areas involved in learning, long term memory, and executive function. Most importantly, it plays a role in neuroplasticity, the ability of the brain to reorganize and remodel itself. Neuroplasticity is impaired in depression and other mental disorders; however, exercise increases BDNF and may be responsible for improvements in cognition and mood.
Endocannabinoids regulate many physiological processes, including movement control, pain processing, and mood. Mechanistic studies in animals demonstrate that exercise-induced endocannabinoids may reduce anxiety and pain perception. Similarly, endogenous opioids, especially the well-known beta-endorphins, a class of compounds famous for their connection to their well-known phenomenon known as "runner's high," are markedly higher after endurance exercise. These two systems may work synergistically to produce some of the beneficial psychological effects of exercise.
While emerging research continues to stack up, it's important to note that the exact nature and extent of the role of exercise for clinical treatment of depression have yet to have been fully elucidated or agreed upon. If you believe you may have a bonafide clinical disorder, please seek out a mental health expert for proper diagnosis and clinical treatment.
Important for the endocrine enhancing properties of exercise. Exerkines are exercise-induced hormonal-like factors which mediate the systemic benefits of exercise through autocrine, paracrine, and/or endocrine properties.
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