The answer is not known. These antibodies may not be the sole cause of the disease, but they are useful markers of disease activity. About one to two percent of teenagers have antibodies. This increases to as high as 20 percent in women over the age of 60. While younger women with these antibodies often have normal thyroid hormone levels, later in life, after years of chronic inflammation, the thyroid may become underactive.
Pregnancy appears to induce a temporary change in the natural progression of thyroiditis.
After delivery, however, the immune system rebounds. Antithyroid antibodies may rise, reaching their highest concentrations at five to seven months postpartum and returning to their pre-pregnancy level at about one year. The thyroid gland is a reservoir that stores large amounts of thyroid hormone. Under normal circumstances, the release of thyroid hormone into the bloodstream is carefully regulated in order for the body's metabolism to remain in balance. When thyroid inflammation occurs, the thyroid gland may become damaged, and large quantities of hormone are released into the blood.