Small intestinal bacterial overgrowth in Alzheimer’s disease
- Karol Kowalski and Agata Mulak
- 2022
Why this matters for your gut health
This research directly informs how we understand the gut–brain connection in Alzheimer’s disease. Small intestinal bacterial overgrowth (SIBO) — an excess of bacteria in the small intestine — was found at nearly twice the rate in Alzheimer’s patients compared to healthy controls. The gut microbiota produces bacterial amyloids and inflammatory compounds like LPS that can cross a leaky gut barrier and potentially reach the brain, accelerating neurodegeneration. Understanding and targeting this gut imbalance could open new therapeutic strategies beyond current drug treatments.
Summary
This pilot study, conducted at Wroclaw Medical University, investigated the prevalence of small intestinal bacterial overgrowth (SIBO) and markers of intestinal inflammation and permeability in 45 Alzheimer’s disease (AD) patients compared to 27 age-matched controls. Using the lactulose hydrogen breath test alongside fecal calprotectin and zonulin ELISA assays, researchers found a significantly higher rate of SIBO in AD patients. However, no significant differences were found in fecal inflammatory markers between the two groups — a finding possibly explained by the anti-inflammatory effects of cholinergic drugs (like acetylcholinesterase inhibitors) that AD patients were already taking.
Key findings
- SIBO was detected in 49% of Alzheimer’s patients versus only 22% of age-matched controls (p = 0.025) — a statistically significant difference, making this the first published report on quantitative gut microbiota disturbances in AD patients.
- SIBO-positive AD patients reported less frequent heartburn compared to SIBO-negative AD patients (9% vs 35%, p = 0.038), suggesting reduced gastric acid secretion may predispose to bacterial overgrowth in the small intestine.
- No significant difference in fecal calprotectin or zonulin levels was found between AD patients and controls — likely because cholinergic drugs used to treat AD have a known anti-inflammatory effect on the gut, potentially masking intestinal inflammation signals.
- There was no association between SIBO and cognitive impairment (MMSE score), age, BMI, or other comorbidities within the AD group, suggesting SIBO may be a widespread but clinically silent phenomenon in this population.
- The gut microbiota’s ability to produce bacterial amyloids and lipopolysaccharides (LPS) — which can increase gut and blood-brain barrier permeability — suggests SIBO could be a contributor to the neuroinflammation seen in Alzheimer’s disease.
Read the full paper
Citation
Kowalski K, Mulak A. Small intestinal bacterial overgrowth in Alzheimer’s disease. Journal of Neural Transmission. 2022;129:75–83