Alpha-synucleinGut-brain axisHydrogen Breath TestIntestinal permeabilityMeta-analysis

Association of small intestinal bacterial overgrowth with Parkinson’s disease: a systematic review and meta-analysis

  • 2021
  • Xiaoqing Li, Xin Feng, Zhongxiang Jiang, et al.
Why this matters for your gut health

Parkinson’s disease (PD) is the second most common neurodegenerative disease after Alzheimer’s, and most patients have gut problems such as slow motility and delayed gastric emptying. Small intestinal bacterial overgrowth (SIBO) may worsen malabsorption, weight loss and the absorption of PD drugs such as levodopa. It may also contribute to inflammation linked to alpha-synuclein. Earlier studies gave conflicting prevalence figures, so this is the first meta-analysis to pool the evidence. The authors say it supports closer attention to gut microorganisms in PD care.

Summary

The authors searched PubMed, EMBASE and the Cochrane Library (from inception to February 2021) for studies linking SIBO and PD. Eleven studies met the inclusion criteria: 7 cross-sectional and 4 cohort studies, with 973 participants (692 PD patients and 281 controls). Ten were rated high quality and one low quality. They pooled SIBO prevalence in PD patients, compared it with healthy controls, and ran subgroup analyses by diagnostic test and region. About half of PD patients tested positive for SIBO, and PD patients were over five times as likely as controls to have it. The prevalence varied by diagnostic test and by region. No clinical predictor of SIBO in PD was found. The authors note limitations, including a small sample size and high heterogeneity from different tests and populations.

Key findings

  • Pooled SIBO prevalence in PD patients was 46% (95% CI 36–56), using a random-effects model because of high heterogeneity (I² = 83%). Egger’s test showed no publication bias (p = 0.0657).
  • Prevalence was higher with the lactulose breath test (LBT) at 51% (95% CI 37–65) than with the glucose breath test (GBT) at 35% (95% CI 20–50). It was highest, at 55% (95% CI 38–72), in the one study that used both tests.
  • Prevalence was 52% (95% CI 40–64) in Western countries versus 33% (95% CI 22–43) in Eastern countries.
  • Across the 11 studies, individual prevalence ranged from 24% (GBT) to 67% (LBT).
  • In 4 case-control studies (278 PD patients, 281 healthy controls), the pooled odds ratio for SIBO in PD was 5.22 (95% CI 3.33–8.19; p < 0.00001), with no heterogeneity (I² = 0).
  • No clear predictors of SIBO in PD were found. Bloating (OR 1.67; p = 0.28), disease duration (p = 0.88), constipation (OR 0.38; p = 0.22) and diarrhea (OR 1.06; p = 0.86) were all non-significant.
  • The authors propose several mechanisms: SIBO may increase intestinal permeability and endotoxin exposure, promote alpha-synuclein expression and neuroinflammation, and impair absorption of PD drugs.
  • SIBO may also reduce bile acid function, impairing fat and vitamin D absorption, which could contribute to weight loss and osteoporosis in PD.
  • The authors suggest that faecal microbiota transplantation and probiotics might be adjuvant therapies for PD, but the study did not test this.
  • Limitations: the sample size was small, and mixed diagnostic methods and populations created heterogeneity. The authors also say Egger’s test could not be run on the case-control analysis because too few studies were included.
  • Minor inconsistencies in the PDF: the abstract and text give a pooled prevalence of 46%, while the Fig. 4 random-effects total shows 47%, and the flow chart (Fig. 1) has some missing numbers. Check the original before citing exact figures.

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Citation

Li X, Feng X, Jiang Z, Jiang Z. Association of small intestinal bacterial overgrowth with Parkinson’s disease: a systematic review and meta-analysis. Gut Pathogens. 2021;13:25. doi:10.1186/s13099-021-00420-w

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