Would you know it if your thyroid gland slowed production of thyroid hormone? Or if it sped up? The symptoms are hard to spot. An out-of kilter thyroid gland causes a variety of puzzling symptoms and many people and doctors mistake them for signs of another disease or normal aging. More than 12 million Americans have thyroid disease, many of whom don't realize it. The Special Health Report, Thyroid Disease: Understanding hypothyroidism and hyperthyroidism explains in easy-to-understand language how to know if your thyroid gland is not functioning as it should and what treatment to follow if your levels are too high or too low.