The thyroid is a butterfly-shaped gland located in the front of the neck. The thyroid produces thyroid hormones and releases them into the blood. Thyroid hormones are important because they control the metabolism of every cell in the body. The thyroid also produces calcitonin, which is involved in calcium regulation.
Most thyroid hormone is secreted in a stable, weak form called T4 (thyroxine) that can last in the bloodstream for over a week. The body’s cells convert T4 into a potent form called T3, which only lasts a few hours.
Thyroid hormone is made from iodine (a special sea salt) and tyrosine (an amino acid from food protein). Most salt in the U.S. is fortified with iodine, but iodine can also be obtained from seafood. There are many plant foods which interfere with the thyroid’s ability to absorb and recycle iodine, including soy, cruciferous vegetables, cassava root, lima beans, and marzipan. See my post Foods that Cause Hypothyroidism for a detailed description of hypothyroidism, how foods interfere in the production of thyroid hormones and dietary recommendations.
Conditions affecting the thyroid include: Graves’ disease (autoimmune hyperthyroidism or “overactive thyroid”), Hashimoto’s Thyroiditis (autoimmune hypothyroidism or “underactive thyroid”), thyroid nodules, goiter (enlarged thyroid/iodine deficiency), and thyroid cancer.