Major influences of the gut microbiota on thyroid metabolism: a concise systematic review

Abstract

The objective was to discuss the influence of the gut microbiota on the functions of the thyroid gland, elucidating the main aspects of rebalancing intestinal function and its importance in the regulation of thyroid functions. The present study followed a systematic review of the literature in periodicals published between 2010 and 2023. The microbiota of the healthy gastrointestinal system presents around 800 species of bacteria, and a hundred of these microorganisms together with bacteriophage viruses and fungi species characterize each human being, with maximum concentration in the colon. In the presence of dysbiosis, the malfunction of the epithelial barrier leads to intestinal and systemic disorders, mainly immunological and metabolic. The functions of the gut microbiota are fundamental and determinant in the metabolism of nutrients, drugs, and hormones, including exogenous and endogenous iodothyronines, as well as micronutrients involved in thyroid homeostasis. The state of the art of effects of the gut microbiota on the regulation of thyroid functions has not been fully elucidated. The intestinal tract is of great importance for the balance of exogenous and endogenous thyroid hormones, but the analysis of the composition of the microbiota is not an easy task. A recent study revealed that individuals with hyperthyroidism had significantly lower levels of Bifidobacteria and Lactobacilli and significantly higher levels of Enterococcus species compared to healthy controls.