Why are thyroid hormones stored in thyroglobulin?

Thyroglobulin serves as the structural framework for the synthesis of thyroxine and triiodothyronine, as well as the storage form of these hormones within the thyroid gland.1

Storing these hormones within thyroglobulin—which is kept in the gland's follicles as the primary component of thyroid colloid—provides a vital reserve of thyroid hormones. This storage mechanism is significant because it likely reflects the historical scarcity of environmental iodine, particularly in terrestrial and freshwater environments. By maintaining this reserve, the body ensures a consistent supply of hormones despite potential fluctuations in dietary iodine intake.21