Probiotic supplements for relieving stress in healthy participants: A protocol for systematic review and meta-analysis of randomized controlled trials.

Background: Psychological stress is a ubiquitous subjectively negative emotional experience, but excessive psychological stress has adverse effects on the happiness in our lives and physical and mental health, and may cause many health problems. Studies have found that probiotics have a certain role in alleviating negative emotions, reducing abnormal behaviors, improving cognitive function, and also showing the great potential of probiotics in relieving psychological stress. At present, many clinical trials have been carried out to intervene in populations with psychological stress with probiotic supplements, but there still lack of targeted systematic review and meta-analysis. Methods and analysis: The Cochrane Central Register of Controlled Trials, Embase, MEDLINE, Psycoinfo, Cumulative Index to Nursing and Allied Health Literature will be searched to obtain the eligible randomized controlled trials published up to March 1, 2019. Meanwhile, the references to relevant publications will also be reviewed to identify other studies, and will re-search before finial summary for analysis. EndNote X7 will be used as a document manager for duplicate checking and screening of literature. The risk of bias will be assessed and the date of included studies will be analyzed by Revman V5.3.5. Results: The primary outcome will be subjective stress level, general mild psychiatric symptoms of participants. The secondary outcome will be cortisol level and adverse effects likely to be related to treatment. Conclusion: The systematic review and meta-analysis will provide evidence to assess the efficacy and safety of probiotics in relieving psychological stress. PROSPERO registration number: PROSPERO CRD42019122930.