Exploring the oral-gut microbiota during thyroid cancer: Factors affecting the thyroid functions and cancer development

Thyroid cancer (TC) is categorized into papillary, follicular, medullary, and anaplastic. The TC is increasing in several countries, including China, the United States, the United Kingdom, Canada, France, Australia, Germany, Japan, Spain, and Italy. Thus, this review comprehensively covers the factors that affect thyroid gland function, TC types, risk factors, and symptoms. Lifestyle factors (such as nutrient consumption and smoking) and pollutants (such as chemicals and heavy metals) increased the thyroid-stimulating hormone (TSH) levels which are directly related to TC prevalence. The conventional and recent TC treatments are also highlighted. The role of the oral and gut microbiota as well as the application of probiotics on TC are also discussed. The variations in the composition of oral and gut microbes influence the thyroid function indirectly through alteration in metabolites (such as short-chain fatty acids) that are eminent for cellular energy metabolism. Maintenance of healthy gut and oral microbiota can help in regulating thyroid function by regulating iodine uptake. Oral or gut microbial dysbiosis can be considered as an early diagnosis factor or TC marker. High TSH during TC can increase the oral microbial diversity while disrupting the high ratio of Firmicutes and Bacteroidetes in the gut. Supplementation of probiotics as an adjuvant in TC treatment is beneficial. However, needs more extensive research to explore the direct effect of probiotics on thyroid function.