The effect of probiotic supplementation on constipation in patients with Parkinson's disease: A randomized controlled...

Background: Constipation is a common non-motor symptom (NMS) in Parkinson's disease (PD), affecting up to 70% of patients and reducing quality of life (QOL). Probiotics may improve bowel function via gut microbiota modulation and gut-brain axis regulation. This randomized, double-blind, placebo-controlled trial evaluated the efficacy of six-week multi-strain probiotic supplementation on constipation in Iranian patients with PD. Methods: Seventy-two patients with PD (aged 50-80 years, functional constipation per Rome IV criteria) were randomized 1:1 to probiotics or placebo. The probiotic capsule contained Lactobacillus acidophilus (L. acidophilus), Lactobacillus casei (L. casei), Lactobacillus rhamnosus (L. rhamnosus), Bifidobacterium lactis (B. lactis), Bifidobacterium longum (B. longum), and Bifidobacterium breve (B. breve) [1 × 10⁹ colony-forming unit (CFU) each, total 12 × 10⁹ CFU/day]. Dietary intake and physical activity were assessed and included as covariates in analysis of covariance (ANCOVA) models. Primary outcome was weekly spontaneous bowel movements (SBMs); secondary outcomes included Patient Assessment of Constipation-Quality of Life (PAC-QOL) and Unified Parkinson's Disease Rating Scale (UPDRS) Part III. Baseline demographic, clinical, dietary, and physical activity characteristics were comparable between groups. Results: The probiotic group showed a mean SBM increase of 3.41 versus 0.44 in placebo [between-group difference = 2.97, 95% confidence interval (CI): 2.46-3.53, P < 0.001]. PAC-QOL improved significantly (adjusted mean difference = -15.22, 95% CI: -22.32 to -8.11, P < 0.001). No significant changes were observed in UPDRS Part III. Conclusion: Six-week probiotic supplementation increased bowel movement frequency and improved constipation-related QOL in patients with PD, with good tolerability. Larger, multicenter trials are warranted to confirm efficacy and explore potential effects on systemic PD progression.