Polyphenol-Rich Functional Herbs Targeting Autoimmune Thyroiditis: Molecular Pathways and Dietary Implications

Hashimoto’s thyroiditis (HT) is the most common autoimmune thyroid disease, affecting approximately 5% of the global population and up to 10% of women in iodine-sufficient regions. Current treatments are limited to hormone replacement and do not address underlying immune dysregulation or tissue damage. This review aims to synthesize current scientific evidence on the immunomodulatory, antioxidant, and microbiome-targeted effects of polyphenol-rich functional herbs in HT. Key bioactive compounds EGCG, curcumin, thymoquinone, and rosmarinic acid were shown to suppress NF-κB and JAK/STAT pathways by 40–70%, enhance Nrf2 signaling 2–3 fold, reduce Th17/Treg imbalance by up to 60%, and inhibit NLRP3 inflammasome activation by 50–70%. Additionally, polyphenols modulate the gut–thyroid axis, increasing SCFA production by 25–45% and restoring tight junction protein expression by 30–60%, thereby reducing antigen leakage and systemic inflammation. However, challenges such as low bioavailability (