Ten days of yeast β-glucan tweaked immune cells and “Th1-type” signals after a tough workout in the heat

Objective 

Test whether 10 days of oral baker’s yeast β-glucan (BYBG) modulates the early immune response to a single bout of strenuous exercise with heat stress in adults of average fitness, focusing on monocytes, T-cell subsets, and serum / lipopolysaccharides (LPS)-stimulated cytokines.

Methods 

• Randomized, double-blind, crossover with two conditions (BYBG vs placebo) and a 7-day washout between conditions.
• BYBG 250 mg/day (baker’s yeast beta-glucan) vs placebo 250 mg/day rice flour, in veggie capsules, consumed with food for 10 days per period. 
• 109 participants completed the protocol. 
• On day 10 of each period, participants performed 90-minute treadmill intervals in a hot, humid chamber (heat index ~51 ± 2 °C). 
• Blood was drawn at baseline, pre-exercise, post (≤5 min), 2 h, and 4 h for flow-cytometric monocyte/T-cell phenotyping (e.g., CD38, CD80, CD86, TLR2, TLR4), serum cytokines (IFN-γ, IL-2, IL-4/5/7, IL-8), and whole-blood LPS-stimulated cytokines. 

Results 

• Monocytes: 
  • BYBG increased post-exercise monocyte concentration vs placebo (post/2 h/4 h), driven mainly by classic monocytes; non-classic monocyte concentration unchanged. 
  • Phenotype: CD38 lower with BYBG (noted p<0.0001 for CD14+ cells); CD80 no change; CD86 increased on non-classic monocytes; TLR2 reduced (classic + non-classic, timing differed by subset); TLR4 increased on non-classic monocytes.
• T cells: 
  • CD4+ T cells: modest increase with BYBG (higher pre-exercise and maintained through recovery vs placebo); TEM and TCM were increased vs placebo. 
  • CD8+ T cells: BYBG increased total CD8+ even before exercise and through 4 h recovery; TEM and TEMRA increased; TCM increased during early recovery (not increased pre-exercise).
• Cytokines: 
  • Serum IFN-γ increased with BYBG (P=0.010). IL-2 approached significance (P=0.050). Other measured serum cytokines/chemokines (e.g., IL-4/5/7, IL-8) not significant.
  • In LPS-stimulated ex vivo cultures, BYBG increased IFN-γ (P=0.038), IL-2 (P=0.001), IL-4 (P=0.0459), IL-7 (P=0.034).

Interpretation 

Short BYBG (250 mg/day × 10 days) modulated innate and adaptive immune signals to strenuous exercise/heat: increased circulating monocytes and T-cells, shifted monocyte pattern-recognition/co-stimulatory markers, and enhanced Th1-leaning cytokine tone (serum and ex vivo LPS responses). These changes are consistent with (but do not prove) improved readiness to respond to antigenic challenges after intense exertion. 

Mechanisms & pathways discussed 

 BYBG-associated changes included pattern recognition receptor/co-stimulatory remodeling on monocytes (decreased TLR2, increased CD86), expansion of effector/central-memory CD8+ subsets, and IFN-γ/IL-2 elevation, thus collectively suggesting Th1-biased, cell-mediated immunomodulation in the acute post-exercise window. 

Dosage & adverse reactions 

BYBG 250 mg/day (veggie capsules) for 10 days; crossover to placebo with 7-day washout. Investigators recorded no supplement-related adverse events. 

Quality of study  

 Strengths: adequately powered completion sample (n=109), double-blind crossover design, standardized heat-stress exercise challenge, multicolor flow-cytometry with prespecified panels, and mixed-model analysis. 

Limitations: short exposure and follow-up (to 4 h post-exercise), immunological surrogates without clinical infection outcomes, and industry collaboration (bias-mitigation procedures followed); early immune dynamics in healthy adults; and translation to infection risk or patient populations are untested here. 

Implications 

For exercise-induced immune perturbation, brief BYBG may tilt post-exercise responses toward Th1/cell-mediated immunity and expand memory/effector T-cells. However, these are hypothesis-generating signals that warrant longer, clinically anchored trials (e.g., illness incidence, vaccine responses).