The thyroid is one of the most important endocrine glands in the body. This gland is found in the neck inferior to (below) the mouth and at approximately the same level as the cricoid cartilage. The thyroid controls how quickly the body burns energy, makes proteins, and how sensitive the body should be to other hormones.

The thyroid participates in these processes by producing thyroid hormones. These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. Iodine is an essential component. The thyroid also produces the hormone calcitonin, which plays a role in calcium homeostasis.

The thyroid is controlled by the hypothalamus and pituitary. The gland gets its name from the Greek word for “shield,” after its shape, a double-lobed structure. Hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) are the most common problems of the thyroid gland.

There are several distinct causes for chronic hypothyroidism. Historically, and in many developing countries, iodine deficiency is the most common cause of hypothyroidism. In present day developed countries, however, hypothyroidism is mostly caused by a lack of a thyroid gland, or a deficiency of hormones from either the hypothalamus or the pituitary.

The most common cause of hypothyroidism is an autoimmune condition named Hashimotos, where the body makes antibodies that slow down the production of the thyroid hormone. Another cause is postpartum thyroiditis, a condition that affects about 5% of all women within a year after giving birth. The first phase is typically hyperthyroidism. Then, the thyroid either returns to normal or a woman develops hypothyroidism. Of those women who experience hypothyroidism associated with postpartum thyroiditis, one in five will develop permanent hypothyroidism requiring life-long treatment.

Hyperthyroidism (or “overactive thyroid gland”) is also caused by the production of antibodies; this condition is known as Graves disease. Other causes are an enlarged thyroid known as goiter, or the development of overactive nodules on the thyroid, which is called Multi Nodular Goiter (MNG). The clinical syndrome is caused by an excess of circulating free thyroxine or free triiodothyronine, or both. Hyperthyroidism is the result of excess thyroid hormone production, causing an increased speed of all the body’s organs.

Thyroid hormone generally controls the pace of all of the processes in the digestive system. This pace is called one’s metabolism. If there is too much thyroid hormone, every function of the body tends to speed up. The thyroid gland regulates the body temperature by secreting two hormones that control how quickly the body burns calories and energy. If the thyroid produces too much hormone, the condition is called hyperthyroidism; but if too little is produced, the result is hypothyroidism.

Cardiovascular disease refers to the class of diseases that involve the heart or blood vessels. While the term technically refers to any disease that affects the cardiovascular system, it is usually used to refer to those related to arterial disease. These conditions have similar causes, mechanisms, and treatments.

Most Western countries face high and increasing rates of cardiovascular disease. Each year, heart disease kills more Americans than cancer. Diseases of the heart alone caused 30% of all deaths, with other diseases of the cardiovascular system causing substantial further death and disability.

It is believed that hypothyroidism is increasing heart disease by increasing LDL, the “bad” cholesterol, and potentially damaging the muscle of the heart. On the other hand, the high level of thyroid hormone production which occurs during hyperthyroidism may cause heart rate disturbances known as arrhythmia, and in rare cases sudden death.