The thyroid gland controls how quickly the body uses energy, makes proteins, and controls how sensitive the body should be to other hormones. It participates in these processes by producing thyroid hormones, the principal ones being triiodothyronine (T3) and thyroxine (T4). The synthesis of T3 and T4 requires adequate amounts of iodine and tyrosine.
Hormonal output from the thyroid is regulated by thyroid-stimulating hormone (TSH) produced by the anterior pituitary, which itself is regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus.
An underactive thyroid gland, referred to as hypothyroidism, is the most common thyroid problem. However, the thyroid gland can also be overactive and this is referred to as hyperthyroidism.