Shreya Desai

Behind the "Runner's High": A Systematic Review and Meta-analysis on the Effects of Exercise on the Endocannabinoid System

Author: Shreya Desai (neuroscience), 2021 Winner ðŸ†

Faculty mentor: Hilary Marusak

Abstract

The endocannabinoid (eCB) system plays a key role in maintaining homeostasis and disruptions in eCB signaling, which have been linked to obesity, anxiety, and depression. Emerging data suggest that the "runner's high" the sense of wellbeing and mood elevation felt after exercise is mediated by the eCB system rather than endorphins, as previously thought. We conducted a PubMed search to identify original research articles published prior to 1/1/2021 that examined the impact of exercise on circulating eCB levels. Thirty-one articles (reporting on 49 samples) were included in the systematic review and ten were included in the meta-analysis. All 31 articles measured levels of the eCB anandamide (AEA) and 25 measured 2-Arachidonoylglycerol (2-AG). The majority of samples (73%) showed a significant increase in AEA following acute exercise whereas results effects on 2-AG were inconsistent. The meta-analysis, however, showed a consistent increase in AEA and 2-AG following acute exercise across modality (e.g., running, cycling) and participants (e.g., animal models, healthy volunteers, patients with pre-existing conditions). However, there was substantial variability in the magnitude of the increase across studies, which may be related to the timing of blood collection and/or fasted state of participants. Interesting, preliminary evidence suggests that the increase in AEA is modulated by intensity, such that more intense exercise (e.g., >70% maximum heart rate) elicits greater increases in AEA. Given that elevated eCB levels are linked to improved mood, reduced stress, pain, and anxiety, enhanced memory, and neuroprotection, increased eCBs may underlie the beneficial effects of exercise on "brain health."

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