What Are Thyroid Hormones?

Thyroid hormones are chemical substances made by the thyroid gland, which is located in the front of the neck. This gland uses iodine to make thyroid hormones, which are essential for the function of every cell in the body. They help regulate growth and the rate of chemical reactions (metabolism), and are involved in the circadian rhythms that govern sleep, among other essential functions.

The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3). Thyroid stimulating hormone (TSH), which is produced by the pituitary gland, acts to stimulate hormone production by the thyroid gland. The pituitary gland is stimulated to make TSH by the hypothalamus gland in the brain.

The thyroid also makes the hormone calcitonin, which is involved in calcium metabolization and stimulating bone cells to add calcium to bone.

T2 is considered necessary for production of the deiodinase enzyme that helps convert T4 into T3. T3 is the ‘active’ hormone that regulates the metabolism and is of short duration in the body. T4 has a much longer half-life in the body. T1’s physiological role was still being evaluated until very recently when it was found that T1 has an influence on the electrical input and charge of the brain and various mental disorders, including multiple sclerosis and Lou Gehrig’s syndrome, which can be a result of not enough T1 to recharge the brain. (1)

1. D. A. Versendaal and Dawn Versendaal-Hoezee, “Contact Reflex Analysis,” Hoezee Marketing, 1993, page 33.