Does Saccharomyces boulardii Increase Secretory IgA in Stool?
Yes, Saccharomyces boulardii does increase secretory IgA (sIgA) levels in stool and intestinal secretions, based on experimental evidence, though this specific immunological outcome has not been the primary focus of major clinical guidelines.
Evidence for sIgA Enhancement
The most direct evidence comes from animal studies demonstrating that S. boulardii administration significantly increases both Helicobacter suis-specific IgA and secretory IgA levels in gastric juice and small intestinal secretions at 12 weeks post-infection 1. This same study showed that S. boulardii also increased production of mouse β-defensin-3 in small intestinal secretions, suggesting broader immunomodulatory effects beyond just sIgA 1.
Additional experimental work demonstrated that S. boulardii can prevent IgA-mediated pathology by regulating mucosal IgA responses, as shown in a model where it prevented oral poliovirus vaccine-induced IgA nephropathy in mice 2. This suggests S. boulardii has complex effects on IgA regulation at mucosal surfaces 2.
Clinical Context and Mechanism
While the AGA conditionally recommends S. boulardii for prevention of C. difficile infection in patients receiving antibiotics (showing a 59% reduction in C. difficile-associated diarrhea recurrence), the mechanism is not fully elucidated 3. The enhancement of sIgA may be one component of its protective immunomodulatory actions 4.
The effective dosing in clinical studies is typically 1g or 3×10¹⁰ CFU/day 4. For maximum immunological benefit, S. boulardii should be started at the beginning of any intervention and continued throughout the treatment course 4.
Important Caveats
- Contraindication in immunocompromised patients: S. boulardii is absolutely contraindicated in immunocompromised individuals due to risk of fungemia 5, 4
- Quality of evidence: The overall quality of evidence supporting S. boulardii's specific effects on intestinal immune function, including sIgA modulation, is rated as low to moderate 4
- Limited human data: Most direct evidence for sIgA enhancement comes from animal models 1, 2, and this specific outcome has not been systematically evaluated in large human clinical trials
Clinical Application
The sIgA-enhancing effect should be considered as part of S. boulardii's broader immunomodulatory actions rather than as an isolated therapeutic target 4. The clinical benefits observed in acute infectious diarrhea (reducing duration by approximately 24 hours) and C. difficile prevention may be partially mediated through enhanced mucosal immunity including sIgA production 6, 3.