The microbiota-gut-testis axis: microbial metabolites as endocrine signals in testosterone regulation

Abstract From a microbial endocrinology perspective, this review evaluates three metabolite classes as candidate testosterone signals. None yet satisfies the three criteria required to establish a microbiota-mediated endocrine role in testosterone regulation—tissue exposure, receptor engagement, and biological effect. Herbal medicines show parallel improvements, but causal evidence is limited. A multi-omics functional validation roadmap is proposed to close these gaps.