06/02/2026
thyroid
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Thyroid hormone production and conversion is an enzymatic process — and like all enzymatic processes, it requires specific cofactors at every step.
Iodine is the raw material for thyroid hormone synthesis — T4 contains four iodine atoms, T3 contains three. But iodine alone is insufficient without:
Selenium, which is required for the selenoenzyme deiodinases (D1, D2, D3) that convert T4 to active T3 — and for glutathione peroxidase activity that protects the thyroid gland from oxidative damage during hormone synthesis. Selenium deficiency alone can produce hypothyroid symptoms with a normal TSH.
Iron, required for thyroid peroxidase (TPO) function — the enzyme that catalyzes iodine incorporation into thyroid hormone. Iron deficiency impairs thyroid hormone synthesis directly.
Zinc, which supports both thyroid hormone production and receptor sensitivity — meaning even adequate hormone levels don't function properly in a zinc-deficient state.
Vitamin D, which modulates immune tolerance and is consistently low in populations with autoimmune thyroid disease.
Gut integrity, because 20% of T4-to-T3 conversion depends on gut bacteria producing the enzyme sulfatase — meaning gut dysbiosis directly impairs thyroid hormone activation.
When you give someone Levothyroxine without evaluating any of these parameters, you're adding fuel to a system that may not be equipped to use it.
Test everything. Address everything.
Struggling with thyroid symptoms despite medication? Get my Free Balance Toolkit — comment BALANCE.
Research: Ventura M, et al. "Selenium and thyroid disease: from pathophysiology to treatment." Int J Endocrinol. 2017;2017:1297658. https://doi.org/10.1155/2017/1297658
