Microbiota and Thyroid Interaction in Health and Disease

The microbiota has been identified as an important factor in health and in a variety of diseases. An altered microbiota composition increases the prevalence of Hashimoto’s thyroiditis (HT) and Graves’ disease (GD). Microbes influence thyroid hormone levels by regulating iodine uptake, degradation, and enterohepatic cycling. In addition, there is a pronounced influence of minerals on interactions between host and microbiota, particularly selenium, iron, and zinc. In manifest thyroid disorders, the microbiota may affect L-thyroxine uptake and influence the action of propylthiouracil (PTU). Although it is relatively well documented that thyroid disorders are linked to the composition of the microbiota, the role of specific genera and the potential use of therapies targeting the microbiota are less clear. The microbiota influences the uptake of iodine, selenium, and iron, and the microbiota may alter the availability of L-thyroxine and toxicity of PTU.Several findings, including the altered microbiota composition in patients with thyroid disorders, the prominent metabolism of thyroid hormones by the microbiota, and that germ-free rats have smaller thyroids than normal rats, support the hypothesis that the gut microbiota also plays a prominent role in thyroid function of the host.A variety of recent studies suggest that the gut microbiota has an enormous impact on human health and disease, and alimentary modulation of the gut microbiota by ingestion of pre, pro-, post-, and synbiotics has been advocated for a variety of diseases.Autoimmune thyroid disorders and metaplastic atrophic gastritis are particularly linked.