The disease appears to be an autoimmune disease. This means that the body's defenses against infection attack the body's own tissue. In the case of Graves' disease, the body appears to be making antibodies that cause the thyroid gland to make more hormone than normal. As a result, the body has too much thyroid hormone. The thyroid gland is key to maintaining normal metabolism.
Metabolism is the rate at which the body's cells do their work.
Metabolism regulates your heart rate, the amount of calories you burn when you are resting, your energy level, and other bodily functions. When thyroid function becomes abnormal, the effects on your body can be dramatic. Many people feel nervous or out of control of their emotions. Some feel muscle weakness, especially in the thigh muscles when going up stairs. A few people notice a swelling in their neck because of an enlarged thyroid.