Sex hormones–Gut microbiome axis: An update of what is known so far

The human gut microbiota is known to be shaped by a wide range of extrinsic factors (geography, lifestyle, sanitation, diet and drugs) and host intrinsic factors (genetics, age, sexual development and sex hormones). The intricate connection between organs, including glands, and different microbiota is well established with emerging evidence linking gut microbiota, composition, diversity and/or function as a key contributor to gut-organ/gland axis signaling. The observed differences in gut microbiota (GM) composition and diversity have led to numerous investigations highlighting the interaction between steroid hormones and the gut microbiome. In this review, we shed the light on how sex steroid hormones may modulate the composition and the function of the gut microbiota and vice-versa, via focusing on a unique crosstalk between these two main actors. We also highlight the role of the gut microbiota in modulating sex steroids signaling along the gut microbiome-sex hormones axis. Altogether, the evidence implies that gonadal steroids and gut microbiota exert a pivotal role in shifting host bacterial action, given the relevance of these factors in directly impacting physiology, metabolism, reproductive efficiency and even in the development of various ailments in both animals and humans.