The thyroid gland is an organ which influences more of metabolic processes than we usually imagine. While it is functioning well, people tend to pay much less attention to this "unappreciated" organ (and the prevention of its disorders) than, for example, to the beauty of the hair. But in fact, thyroid is vital. 
Consequences of its disorders may vary greatly from goiter (enlarging of a gland) and up to cancer. 
To avoid all these problems, the production of thyroid hormones must be kept in balance. So notice that overproduction of thyroid hormones carries risks as well as hypothyroidism (low thyroid hormones level).