Latest article: The gut-immune-thyroid axis: Examining the impact of the gut on thyroid autoimmunity
Date
05 May 2026
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Autoimmune thyroid diseases (AITDs) are among the most common autoimmune diseases, affecting approximately 5% of individuals worldwide, with an increasing incidence.¹ They are characterised by a dysfunctional immune system, which loses self-tolerance, negatively targeting the thyroid gland.²
The most frequent forms of AITD include Graves' Disease and Hashimoto's thyroiditis, though other immunogenic destructive forms of AITD also exist, including postpartum thyroiditis.² While Hashimoto’s and Graves’ Disease may manifest with seemingly different clinical symptoms, the gut-immune-mediated mechanisms that underlie both conditions are similar, as are the underlying root causes.³
THE GUT-IMMUNE-THYROID AXIS
A multi-directional signalling axis exists between the thyroid, gastrointestinal tract and immune system. For example:
• Thyroid hormones are essential for influencing gut motility and secretory activity, thereby influencing the environment in which the gut bacteria develop. Inadequate production of thyroid hormones may result in increased gastric pH, leading to bacterial overgrowth, which contributes to loss of immune tolerance.⁴
• The gut bacteria themselves also influence thyroid physiology, for example, via regulating iodine uptake, breakdown and intestinal-hepatic cycling of thyroid hormones.⁵
• Gut dysbiosis can impair deiodinase activity, which is crucial in converting T4 into T3.⁶
Key highlights
- The gut-immune-thyroid axis highlights a multi-directional signalling pathway that may prime or ameliorate autoimmune thyroid disease (AITD).
- Individuals with AITD demonstrate alterations in both gut composition and function, which may increase risk of AITD.
- Modifying the intestinal microbiome, with a focus on improving microbial composition, may help regulate the immune system and thus conserve thyroid function.
- Selenium, iodine and vitamin D all assist with reducing thyroid antibodies but also exert their mechanism of action under the direction of the gut microbiome.
- A Mediterranean diet with a specific focus on fibre intake may be a useful adjunct for modulating the immune system in AITD.