# Effects of Physical Exercise on Circulating Serotonin Levels: A Systematic Review and Meta-Analysis

## TL;DR

This study reviews whether physical exercise affects serotonin levels in the blood, finding no significant impact based on current evidence.

## Contribution

The novelty lies in conducting a systematic review and meta-analysis focused on the effect of physical exercise on circulating serotonin levels.

## Key findings

- Physical exercise showed a non-significant effect on circulating serotonin levels.
- High heterogeneity among studies suggests variability in results.
- Current evidence is limited to female participants and lacks generalizability.

## Abstract

Serotonin is a neurotransmitter that plays a crucial role in mood regulation and has several health-related functions in humans. Physical exercise (PE) has been proposed as a potential non-pharmacological strategy to modulate serotonin levels. Objective: This systematic review and meta-analysis aimed to investigate the effect of PE on circulating serotonin concentrations. Methods: Following PRISMA guidelines, a systematic search was conducted in PubMed, Web of Science, and Scopus, identifying 938 records. Randomized controlled trials with a PE intervention group and a non-PE usual care control group that meet the inclusion criteria were selected. Data were synthesized using a random-effects meta-analysis with standardized mean differences (SMD), and sensitivity analyses were performed using alternative pre–post correlation assumptions (r = 0.6–0.9). Study quality was assessed using the PEDro scale. Results: Five randomized controlled trials comprising 116 participants, all of them females, were included. The pooled analysis showed a non-significant effect of PE on circulating serotonin levels (SMD 1.48; p = 0.135; 95% CI −0.46 to 3.42), with extremely high heterogeneity (I2 = 94.63%). Sensitivity analyses produced similar non-significant results and consistently high heterogeneity, indicating robustness of the original model. Methodological quality ranged from acceptable to good (PEDro scores 4–7). Conclusions: Current evidence, derived exclusively from female participants, does not support a significant effect of PE on serum or plasma serotonin levels. The substantial heterogeneity among studies and the generally moderate methodological quality limit the strength of the conclusions and generalizability of the conclusions. Further, high-quality randomized controlled trials with standardized measurement protocols are needed to clarify the influence of exercise on circulating serotonin levels.