The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are produced by the thyroid gland. The major form of thyroid hormone in the blood is thyroxine (T4); in fact, there is generally 20 times more T4 in the blood than T3. The thyroid hormones are essential to the proper development and differentiation of all cells of the human body.* The thyroid hormones regulate the metabolism of proteins, fats, and carbohydrates, affecting how humans use these compounds to produce energy.* Thyroid hormones have important functions in the body; for example, thyroxine supports cardiac output, heart rate, respiratory rate, and basal metabolic rate.*
The thyroid gland cannot produce its hormones without the presence of the amino acid L-tyrosine and the mineral iodine.* Thus, a deficiency of either the amino acid or the mineral or both could contribute to low thyroid hormone levels.* Studies have found L-tyrosine may be beneficial for treating fatigue, a common symptom of low thyroid hormone levels.*
Individuals should be aware that some foods can cause a relative iodine deficiency by binding to iodine, making it inaccessible for thyroid hormone production, although cooking these foods tends to make them less so. Such foods include broccoli, cauliflower, cabbage, Brussels sprouts, kale, soy, peanuts, pine nuts, turnips, and rutabaga.
Tyrosine is also an important cofactor for adrenal neurotransmitter synthesis, as it is converted In the adrenal glands into dopamine, norepinephrine, and epinephrine.*