How Gut Microbiota Affects Thyroid Function
The composition of gut microbiota has a significant impact on the human body. Studies conducted so far have found a correlation between dysbiosis and a range of diseases, including thyroid disorders (primarily autoimmune, but also the occurrence of nodules or thyroid cancer).
Autoimmune Thyroid Diseases
Autoimmune thyroid diseases are the most common organ-specific autoimmune diseases with a prevalence of 2–5% of the population. They often occur together with gastrointestinal diseases, likely due to a compromised intestinal barrier and subsequent increase in intestinal permeability, allowing antigens to penetrate the intestinal wall and activate the immune system. Patients with Graves' disease or Hashimoto's thyroiditis often also test positive for antibodies against gliadin, transglutaminase, and the yeast Saccharomyces cerevisiae.
The composition of gut microbiota affects the thyroid through various mechanisms. Essential micronutrients for thyroid function are absorbed in the gut – iodine, iron, and copper are important for the synthesis of thyroid hormones, selenium and zinc for the conversion of free thyroxine (fT4) to free triiodothyronine (fT3), and vitamin D regulates the immune response. These micronutrients are often deficient in patients with thyroid diseases. Some bacterial species can also induce cross-reactivity of antibodies with thyroid peroxidase and thyroglobulin (e.g., Lactobacillus spp. and Bifidobacterium spp.).
Influencing Medication Dosage
The first step in treating patients with autoimmune thyroid diseases is to restore euthyroidism, through thyroid hormone replacement in hypothyroidism, or specific antithyroid drugs in hyperthyroidism. Correct treatment settings are influenced by many factors: age, gender, changes in BMI, etiology of thyroid dysfunction, temporary use of other drugs, changes in dietary habits, intake of soy proteins, gastrointestinal malabsorption, infections, bariatric surgery, atrophic gastritis, cystic fibrosis. All these situations can simultaneously affect drug absorption and thus the severity of thyroid dysfunction. The composition of gut microbiota can also influence the availability of L-thyroxine and the toxicity of antithyroid therapy.
Probiotics in the Treatment of Thyroid Diseases
Probiotics are non-pathogenic living microorganisms that, when ingested, influence the composition of gut microbiota. Their administration is suggested as a therapeutic option for many diseases, including thyroid diseases. Data suggest that for thyroid diseases, just as for many others, supplementation with Lactobacillaceae spp. and Bifidobacteria spp. is beneficial. These two strains are often reduced in the microbiota of patients with thyroid diseases.
Conclusion
Gut dysbiosis is common in patients with thyroid diseases. The composition of gut microbiota affects the development of autoimmune thyroid diseases and the absorption of micronutrients necessary for proper thyroid function (iodine, selenium, zinc, iron). Probiotics have a positive effect on gut microbiota and could, therefore, represent an adjunctive treatment for autoimmune thyroid diseases.
(epa)
Sources:
- Docimo G., Cangiano A., Romano R. M. et al. The human microbiota in endocrinology: implications for pathophysiology, treatment, and prognosis in thyroid diseases. Front Endocrinol (Lausanne) 2020 Dec 4; 11: 586529, doi: 10.3389/fendo.2020.586529.
- Fröhlich E., Wahl R. Microbiota and thyroid interaction in health and disease. Trends Endocrinol Metab 2019; 30 (8): 479–490, doi: 10.1016/j.tem.2019.05.008.
- Knezevic J., Starchl C., Tmava Berisha A., Amrein K. Thyroid-gut-axis: how does the microbiota influence thyroid function? Nutrients 2020 Jun 12; 12 (6): 1769, doi: 10.3390/nu12061769.
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