Graves' Disease is a type of autoimmune disease that causes over-activity of the thyroid gland, causing hyperthyroidism. This over-activity is also sometimes called "toxic diffuse goiter." The thyroid gland helps set the rate of metabolism, which is the rate at which the body uses energy. When the thyroid is too active, it makes more thyroid hormones than the body needs. High levels of thyroid hormones can cause side effects such as weight loss, rapid heart rate and nervousness. This is an uncommon disease that affects 2 percent of all women at some time in their lives. Graves’ Disease also tends to affect women between the ages of 20 and 40, although it occurs in infants, children, and the elderly.