Overview

The thyroid is a vitally important hormonal gland that plays an essential role in metabolism, growth, and maturation of the human body. The thyroid produces and releases into the circulation at least two potent hormones, thyroxine (T₄) and triiodothyronine (T₃), which influence basal metabolic processes and enhance oxygen consumption in nearly all body tissues. Thyroid hormones also influence growth, temperature regulation, lipid and carbohydrate metabolism, cardiac myocyte activity, reproduction, cognitive functioning, and bone development.

Hypothyroidism is the insufficient production of thyroid hormone. Overt hypothyroidism is present in 0.1-2% of all adults, with 15% of older women meeting the criteria for subclinical hypothyroidism.¹ Worldwide, iodine deficiency is the most common cause of hypothyroidism. In the United States, where salt is fortified with iodine, autoimmune thyroiditis or Hashimoto's thyroiditis is the most common type of hypothyroidism. In autoimmune thyroiditis there is cell-mediated antibody destruction of the thyroid gland. The second leading cause of hypothyroidism is iatrogenic—including situations when surgery, medications, or radiation have affected the functioning of the gland.²

Because the thyroid affects so many different physiologic processes in the body, the clinical signs of hypothyroidism are variable from one individual to another. Some patients present with mild symptoms in spite of having low levels of circulating thyroid hormones, while some patients have more significant symptoms despite only mildly abnormal lab testing.

Common Symptoms of Hypothyroidism²

• Fatigue
• Dry skin and nails
• Cold intolerance
• Hair loss
• Concentration or memory problems
• Constipation
• Weight gain
• Bradycardia and hypothermia
• Carpal tunnel symptoms
• Menorrhagia, irregular menses, or infertility