Across 5 studies, all reported beneficial effects of Saccharomyces cerevisiae on immune function, with effect sizes ranging from small to moderate. The strongest evidence comes from a systematic review (n=640) showing small beneficial effects and a clinical trial in chicks (n=216) showing moderate benefits. No consistent dose, form, or study duration data were reported across studies, and populations studied varied widely (humans, chicks, animals, in vitro).
Caveats: Available evidence is overwhelmingly positive — clinical literature in this area is subject to publication bias (null-result studies are less likely to be published or indexed). Many of the included studies did not reach statistical significance — effect may be smaller than the predominant direction suggests. Evidence base is small (only 5 studies) — conclusions should be considered preliminary. Only one study was a systematic review of human trials; other studies were in animals or in vitro, limiting generalizability to humans.
Several nutraceuticals and probiotics may also have some role in enhancing immune functions.
improved ... the immune status ... and the immune response to Newcastle disease virus (NDV) and avian influenza (AI)
functional foods, including dairy proteins and hydrolysates, plant-based functional foods, fermentates... Our findings reveal four key immunity boosting mechanisms by functional foods
They enhance antioxidant enzymes... promote the maturation and function of immune cells, and increasing secretory IgA production.
MTE administration alleviated body weight loss, restored organ morphology, and increased immune cytokines (TNF-α and IFN-γ) in immunosuppressed mice.
Investigation of host-microbiome interactions confirmed the immunomodulatory potential of the applied test product.