“The thyroid is a small gland at the front of your neck that makes the thyroid hormone that regulates your metabolism, says Dr. Thomas J. Fahey III,  Chief of Endocrine Surgery, and Director of the Endocrine Oncology Program. “The thyroid has a wide-ranging effect throughout the body. It contributes to how fast your heart beats, how fast your hair grows, and how fast things pass through your intestines,” Dr. Fahey says.

The thyroid gland commonly malfunctions, typically by over- or under-producing hormones. An over-functioning thyroid gland can trigger “hyperthyroidism,” which can cause your body to race and your heart to pound, as well as weight loss, sleep trouble, muscle weakness, frequent or loose bowel movements, nervousness, or irritability. The most common cause of hyperthyroidism in the U.S. is Graves’ disease, an autoimmune disorder in which the immune system attacks the thyroid gland. An under-functioning thyroid, which frequently stems from the autoimmune disorder Hashimoto’s disease, may lead to “hypothyroidism” and resulting fatigue, weight gain, depression, constipation, heavy or irregular menstrual periods, or problems conceiving. Family history increases the risk for both Hashimoto’s and Graves’.”

Weill Cornell Medicine (https://weillcornell.org/news/understanding-thyroid-problems-disease)