Probiotic intake and mental health in healthy working adults: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND: Workers face significant mental health challenges from stress, anxiety, and depression, impacting individuals, organizations, and society. Emerging research indicates a link between the gut microbiome and mental well-being, suggesting probiotics as a potential support. This study objectively evaluated probiotic supplementation's effects on depression, anxiety, stress, sleep, and related biological markers in this population. METHODS: We conducted a systematic review and meta-analysis following PRISMA 2020 guidelines. EMBASE, Cochrane Library, and PubMed were searched for randomized controlled trials assessing probiotic supplementation on a range of psychological outcomes. The primary outcomes were perceived symptoms of depression, anxiety, stress, and sleep quality. The secondary outcomes were physiological markers of mental health, such as cortisol and C-reactive protein levels, in working populations. Eligible studies included healthy employed adults (≥ 18 years), without psychiatric, neurodegenerative, genetic, infectious, or endocrine disorders, including pregnancy. RESULTS: Twelve studies involving 3,350 participants were incorporated. Probiotic consumption had a modest yet statistically significant positive effect on subclinical psychological outcomes, including symptoms of depression, anxiety, and stress, in healthy working adults (standardised mean difference (SMD) = -0.21, 95% CI [-0.34, -0.09], p = 0.001). These findings were maintained despite moderate statistical heterogeneity that was likely due to variations in probiotic strains, dosages, and duration of supplementation used. Moreover, the probiotic interventions were associated with a statistically significant reduction in cortisol levels, a key biomarker of physiological stress (SMD = -0.26, 95% confidence interval [CI] [-0.45, -0.08], p = 0.005). Conversely, no statistically significant effects were observed for probiotic supplementation on the C-reactive protein levels, a marker of systemic inflammation. However, due to the lack of available evidence, it was impossible to draw firm conclusions about the effects of probiotics on sleep quality and biomarkers of oxidative stress. CONCLUSION: This systematic review and meta-analysis provide preliminary evidence suggesting that probiotic supplementation may hold promise as an approach to improve mental well-being within working populations. However, further high-quality randomised controlled trials targeting this population are needed to determine the optimal probiotic strains, dosages, and treatment durations for addressing specific mental health outcomes. TRIAL REGISTRATION: PROSPERO number CRD42024510170.