How are FT3 and allergy related?

The relationship between free triiodothyronine (FT3) and allergies is complex and not fully established. FT3, the active thyroid hormone, modulates immune function—it can influence T-cell activity, mast cell degranulation, and cytokine profiles. Some observational studies suggest an association between low FT3 levels and increased allergy risk, while others indicate thyroid hormones may exacerbate allergic responses. However, evidence is mostly mechanistic or from observational studies; no strong RCTs confirm causality. Additionally, thyroid disorders (e.g., Hashimoto's) can have allergic components themselves. Direct DNA testing for FT3 levels is not possible; FT3 is measured via blood test. Genetic variants like GPX1 (selenium-dependent) may indirectly affect thyroid function but not specifically allergies. Conclusion: A link likely exists but is insufficiently proven for clinical decisions. Evidence: human-moderate.