Gut Microbiota Changes and Its Potential Relations with Thyroid Disorders: From Composition to Therapeutic Targets

Abstract

Composed of over 1200 species of anaerobes and aerobes bacteria along with bacteriophages, viruses, and fungal species, the human gut microbiota (GM) is vital to health, including digestive equilibrium, immunologic, hormonal, and metabolic homeostasis. Micronutrients, usually refer to trace elements (copper, iodine, iron, selenium, zinc) and vitamins (A, C, D, E), interact with the GM to influence host immune metabolism. So far, microbiome studies have revealed an association between disturbances in the microbiota and various pathological disorders, such as anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, anxiety, depression, early-onset cancers, type 1 diabetes (T1D) and type 2 diabetes (T2D). As common conditions, thyroid diseases, encompassing Graves' disease (GD), Graves' orbitopathy (GO), Hashimoto's thyroiditis (HT), benign nodules, and papillary thyroid cancer (TC), have negative impacts on the health of all populations. Following recent studies, GM might play an integral role in triggering diseases of the thyroid gland. Not only do environmental triggers and genetic predisposing background lead to auto-aggressive damage, involving cellular and humoral networks of the immune system, but the intestinal microbiota interacts with distant organs by signals that may be part of the bacteria themselves or their metabolites. The review aims to describe the current knowledge about the GM in the metabolism of thyroid hormones and the pathogenesis of thyroid diseases and its involvement in the appearance of benign nodules and papillary TC. We further focused on the reciprocal interaction between GM composition and the most used treatment drugs for thyroid disorders. However, the exact etiology has not yet been known. To elucidate more precisely the mechanism for GM involvement in the development of thyroid diseases, future work is needed.

Keywords: Graves’ disease; Graves’ orbitopathy; Hashimoto’s thyroiditis; gut microbiota; thyroid cancer; thyroid nodules.

Figure 1

The interrelationship between gut microbiota dysbiosis and thyroid dysfunction. Under physiological conditions, the thyroid gland and GM have a mutually beneficial association. When thyroid function or GM homeostasis changes, the other party would be influenced. In other words, the differences in GM can lead to the development of thyroid dysfunction, and the development of the thyroid gland can cause a series of endocrine changes, leading to the differences in GM.

Figure 2

A schematic overview of main mechanisms of gut microbiota influencing thyroid diseases, including AITD, PHT, TN and TC.