Why is iodine needed for thyroid hormones?

Iodine is essential for the production of thyroid hormones because it is a fundamental chemical component of their structure. The two primary thyroid hormones, thyroxine and triiodothyronine, are synthesized by attaching iodine atoms to the amino acid tyrosine within a protein called thyroglobulin.12

Specifically, thyroxine contains four iodine atoms, while triiodothyronine contains three. Because these hormones cannot be produced without iodine, the body must obtain this element through the diet. Once ingested, the thyroid gland actively concentrates inorganic iodide from the bloodstream to facilitate this synthesis. These hormones are vital for regulating metabolism, heart action, nerve responses, and physical growth. When dietary iodine is insufficient, the body cannot produce adequate amounts of these hormones, which can lead to conditions such as goitre and hypothyroidism.2134