Lactobacillus in autoimmune thyroid diseases: benefit or risk?
TL;DR
Overall, Lactobacillus-related interventions remain investigational, and future studies should prioritize standardized strain identification, disease-specific mechanisms, long-term safety, and well-designed clinical trials.
Abstract
Autoimmune thyroid diseases (AITDs), mainly Hashimoto’s thyroiditis and Graves’ disease, are common organ-specific autoimmune disorders driven by complex interactions among genetic susceptibility, immune dysregulation, environmental exposure, and microbial factors. Increasing evidence supports the relevance of the gut–thyroid axis, in which gut microbiota may influence thyroid hormone metabolism, intestinal barrier integrity, systemic inflammation, and thyroid-directed autoimmunity. Among gut commensals, Lactobacillus-related taxa have attracted attention because selected strains can modulate cytokine production, Treg/Th17 balance, short-chain fatty acid metabolism, epithelial barrier function, and inflammatory signaling pathways such as TLR4/NF-κB, AhR, and PPARδ-related pathways. However, most mechanistic evidence is derived from non-AITD animal, cellular, or metabolic disease models, and direct validation in AITD patients remains limited. This review summarizes current evidence on Lactobacillus-related strains in AITDs, emphasizing strain-specific effects, updated taxonomy, mechanistic plausibility, clinical heterogeneity, and translational limitations. We also discuss inconsistent microbial signatures, neutral or inconclusive clinical findings, and safety concerns, including probiotic-associated infection, antibiotic resistance genes, horizontal gene transfer, and potential pro-autoimmune effects. Overall, Lactobacillus-related interventions remain investigational, and future studies should prioritize standardized strain identification, disease-specific mechanisms, long-term safety, and well-designed clinical trials.