Probiotics nudge athletes' immune markers in the right direction

Hard training is a double-edged sword for the immune system: intensive blocks of training and competition can compromise athletes' immune function and elevate inflammatory responses, which is one reason athletes are notorious for picking up infections at exactly the wrong time. Probiotics are among the most widely studied nutritional counters to this, but previous meta-analyses have reported inconsistent findings on whether they actually work. That inconsistency is precisely what an umbrella review is built to resolve, by pooling the pooled evidence and re-analysing it under one framework.

The researchers systematically searched PubMed, Cochrane Library, Web of Science, EMbase and Scopus for meta-analyses published up to 1 December 2025, and supplemented these with recent randomised controlled trials up to 15 December 2025. Quality was assessed with AMSTAR2 and GRADE, overlap between reviews was checked with the GROOVE tool, and the data were re-analysed using random- or fixed-effects models. The final analysis incorporated five meta-analyses covering 69 RCTs plus one additional recent trial, totalling 3,413 participants, with outcomes including TNF-α, IL-6, IL-8, IL-10, secretory IgA and IFN-γ.

Probiotic supplementation significantly reduced the pro-inflammatory marker TNF-α, with an effect size of -0.59. It also significantly increased secretory IgA, the antibody that defends the body's mucosal surfaces (effect size 0.30), and raised IFN-γ levels. The picture was not uniformly positive, however: no significant effects were observed for IL-6, IL-8 or the anti-inflammatory cytokine IL-10. So the pooled evidence points to selective shifts in specific immune markers rather than a blanket anti-inflammatory effect.

Individual meta-analyses on probiotics in athletes had pointed in different directions, and this re-analysis helps explain why: the effect appears marker-specific, showing up clearly for TNF-α, secretory IgA and IFN-γ but not for other cytokines. The authors conclude the evidence supports probiotics as a strategic nutritional approach for immune protection in athletes. The big open questions are strain-specific efficacy and optimal dosing, which they flag as priorities for future research before personalised recommendations are possible.

If you train hard and often, this is a reason to think probiotic supplementation can shift some immune and inflammatory markers in a favourable direction — particularly lowering TNF-α and supporting mucosal immunity via secretory IgA. It is worth being clear about what this does not show: these are changes in laboratory markers, not proof that supplementing means fewer colds or missed sessions. With strain and dose questions still open, the evidence supports the concept more strongly than any particular product.