Can zinc deficiency impair thyroid function and immune regulation?

Zinc is an essential trace mineral that serves as a vital structural, regulatory, and immunological cofactor, playing a multi-faceted role in thyroid hormone homeostasis and immune tolerance.

Thyroid hormone metabolism

• Deiodinase activation: Zinc is required to maintain the structural integrity and 3D conformation of iodothyronine deiodinases, particularly type II deiodinase (D2), which facilitates the peripheral conversion of thyroxine (T4) to active triiodothyronine (T3).
• Hormonal regulation: Deficiency impairs this conversion and disrupts the central regulation of thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH). Correcting a baseline zinc deficiency has been shown to improve free T3 levels and raise the free T3 to free T4 ratio.

Thyroid hormone receptor function

• Structural integrity: Thyroid hormone receptors (TRα and TRβ) rely on zinc to coordinate two canonical C4-type zinc-finger motifs within their DNA-binding domains.
• Transcriptional signaling: Zinc depletion or chelation destabilizes these zinc-finger domains, preventing the receptor from binding to thyroid hormone response elements (TREs) on DNA, abolishing receptor dimerization, and blocking downstream gene transcription.

Immune regulation and autoimmunity

• Treg/Th17 imbalance: Zinc deficiency drives a pro-inflammatory shift by promoting pathogenic Th17 polarization through enhanced Smad signaling and rendering T-regulatory (Treg) cells dysfunctional via decreased miR-146a expression.
• Autoimmune thyroiditis link: This Th17/Treg imbalance directly mirrors the core pathophysiology of autoimmune thyroid diseases, such as Hashimoto's thyroiditis. While zinc sufficiency restores this balance by inhibiting IL-6–STAT3 signaling, clinical trials evaluating zinc supplementation to reduce human thyroid autoantibodies show mixed and limited results.

Bottom line

• Key takeaway: Zinc deficiency directly compromises thyroid function by impairing the enzymatic conversion of T4 to active T3, disrupting thyroid hormone receptor DNA-binding, and promoting a pro-inflammatory Treg/Th17 immune imbalance characteristic of autoimmune thyroiditis.