When the thyroid works, the mind keeps up

The thyroid as the pacemaker of metabolism

The thyroid is a butterfly-shaped organ in the neck that produces the hormones thyroxine (T4) and triiodothyronine (T3). These hormones control almost every cell in the body — from heat regulation and energy turnover to the development of the nervous system.

To form these hormones, the thyroid needs sufficient iodine as raw material. A second trace element, selenium, is involved in converting the hormones into their more active form. The two minerals complement each other at different points in the same biological process.

The European Food Safety Authority (EFSA) has reviewed the scientific evidence on iodine and selenium. On this basis the EU Commission has authorised health claims, which Magnetitpfad presents below for each mineral separately.

From trace element to hormone: the path through the body

Iodine as a building block of thyroxine and triiodothyronine

After absorption from food, iodide reaches the thyroid through the bloodstream. There it is moved into the thyroid cells by an active transport mechanism, the sodium-iodide symporter, and then bound to tyrosine residues of the protein thyroglobulin. From this binding, monoiodotyrosine and diiodotyrosine first arise, which combine into the finished hormones T4 and T3.

“Iodine contributes to normal thyroid function” — Under Regulation (EU) No 432/2012

Without an adequate iodine intake, the thyroid cannot form enough hormone, which, via a feedback mechanism, leads to increased secretion of thyroid-stimulating hormone (TSH) from the pituitary gland.

Selenium as a cofactor of the deiodinase enzymes

The T4 released by the thyroid is regarded as the storage form and must first be converted into the more active T3 in many target tissues. This conversion is carried out by selenium-containing deiodinase enzymes, which split an iodine atom off the T4 molecule. In these enzymes selenium is present as selenocysteine — a rare amino acid that occurs in only a few protein families.

“Selenium contributes to normal thyroid function” — Under Regulation (EU) No 432/2012

The cognitive side: why iodine is listed separately here

Thyroid hormones are involved in the maturation of nerve cells as early as brain development and remain important for neuronal signal transmission in adulthood as well. Because these hormones cannot be formed without iodine, the trace element is granted a second, independent EU claim alongside thyroid function.

“Iodine contributes to normal cognitive function” — Under Regulation (EU) No 432/2012