Background Parkinson’s disease (PD) is the second most common neurodegenerative disease worldwide. Gut dysbiosis is hypothesized to cause PD; therefore, whether probiotics can be used as adjuvants in the treatment of PD is being actively investigated. Aims We performed a systematic review and meta-analysis to evaluate the effectiveness of probiotic therapy in PD patients. Methods PUBMED/MEDLINE, EMBASE, Cochrane, Scopus, PsycINFO and Web of Science databases were searched till February 20, 2023. The meta-analysis used a random effects model and the effect size was calculated as mean difference or standardized mean difference. We assessed the quality of the evidence using the Grade of Recommendations Assessment, Development and Evaluation (GRADE) approach. Results Eleven studies involving 840 participants were included in the final analysis. This meta-analysis showed high-quality evidence of improvement in Unified PD Rating Scale Part III motor scale (standardized mean difference [95% confidence interval]) (− 0.65 [− 1.11 to − 0.19]), non-motor symptom (− 0.81 [− 1.12 to − 0.51]), and depression scale (− 0.70 [− 0.93 to -0.46]). Moderate to low quality evidence of significant improvement was observed in gastrointestinal motility (0.83 [0.45–1.10]), quality of life (− 1.02 [− 1.66 to − 0.37]), anxiety scale (− 0.72 [− 1.10 to − 0.35]), serum inflammatory markers (− 5.98 [− 9.20 to − 2.75]), and diabetes risk (− 3.46 [− 4.72 to − 2.20]). However, there were no significant improvements in Bristol Stool Scale scores, constipation, antioxidant capacity, and risk of dyslipidemia. In a subgroup analysis, probiotic capsules improved gastrointestinal motility compared to fermented milk. Conclusion Probiotic supplements may be suitable for improving the motor and non-motor symptoms of PD and reducing depression. Further research is warranted to determine the mechanism of action of probiotics and to determine the optimal treatment protocol.

Parkinson’s disease (PD) is the second most common neurodegenerative disease. It is believed that “gut dysbiosis” can cause PD; therefore, whether probiotics can be used as adjuvants in the treatment of PD is being actively investigated. We performed a systematic review and meta-analysis to evaluate the effectiveness of probiotic therapy in PD patients. PUBMED/MEDLINE, EMBASE, Cochrane, Scopus, PsycINFO and Web of Science databases were searched till January 9, 2023. The meta-analysis used a random effects model and the effect size was calculated as mean difference or standardized mean difference. Ten studies with 760 participants were included in the final analysis. The meta-analysis revealed a significant improvement in gastrointestinal motility (standardized mean difference [95% confidence interval]) (0.78 [0.57-0.98]) and antioxidant capacity (1.73 [0.26 to 3.21]). Serum inflammatory markers (-8.64 [-16.05 to -1.23]), diabetes risk (-3.41 [-4.65 to -2.17]), Unified PD Rating Scale Part III (-4.12 [-7.81 to -0.43]), non-motor symptom (-5.55 [-8.30 to -2.80]), quality of life (-1.13 [-1.86 to -0.40]), anxiety scale (-2.21 [-3.41 to -1.00]) and depression scale (-1.53 [-1.99 to -1.07]) demonstrated a significant decrease. The Bristol stool scale, constipation and risk of dyslipidemia were not significantly improved. In a subgroup analysis, capsules further improved gastrointestinal motility than fermented milk. This review found that probiotic supplements may be suitable for increasing gastrointestinal motility, reducing inflammation, and improving motor and non-motor symptoms of PD. Further research is warranted to determine the mechanism of action of probiotics and the optimal treatment protocol.