Hypothyroidism is a condition in which the thyroid, a gland located in the neck, makes too little thyroid hormone. Thyroid hormone is important in regulating the body's use of energy, fats, and protein. The symptoms of hypothyroidism include tiredness, intolerance to cold, muscle aches and stiffness, dry skin, and constipation. It is well known that if people with hypothyroidism severe enough to cause symptoms and abnormal thyroid laboratory tests are not treated, their risk for heart disease increases. However, many older persons who have no symptoms have thyroid tests that suggest a milder degree of hypothyroidism (sometimes called subclinical hypothyroidism).