Investigating the Link between the Intestinal Microbiome and Th17/Treg Dysregulation in Hashimoto’s Thyroiditis, and the Therapeutic Potential of Vitamin D

Autoimmune disease (AD) has become a leading cause of illness in the twenty-first century, with autoimmune thyroid disease at the forefront of these conditions. Hashimoto's thyroiditis (HT) shares many features with other ADs, including associations with gastrointestinal symptoms linked to intestinal dysbiosis (ID). However, the pathogenesis of HT remains incompletely understood, particularly the role of specific T cell lymphocyte activity. The primary objective of this review was to investigate links between ID and HT pathogenesis, focusing on the relationship between a specific cluster of differentiation 4 (CD4) T cell subsets including T helper 17 (Th17) and regulatory T cells (Treg). A secondary aim was to explore whether vitamin D supplementation may serve as a viable intervention in managing HT, given existing research demonstrating links between Vitamin D status, HT pathogenesis and ID. ID may play a contributory role in HT pathogenesis through immune modulation involving CD4+ T cell subsets. Vitamin D supplementation demonstrates potential as an adjunctive strategy; however, further targeted human studies are required to clarify causality and therapeutic efficacy.