Natural Health from A to Z – Thyroid Health — Margaret Durst. The thyroid gland is the body’s internal thermostat, regulating the temperature and controlling how quickly the body burns calories and uses energy. If the thyroid is overactive and secretes too much hormone, the condition is known as hyperthyroid. If the thyroid is underactive and secretes too little hormone, the condition is called hypothyroid. Hypothyroidism affects about 13 million people in the United States.