However, bone density measurements have demonstrated that bone loss is common in patients with overt hyperthyroidism and, to a lesser extent, in those with subclinical hyperthyroidism. A history of overt hyperthyroidism is a risk factor for hip fracture later in life, which in turn is one of the causes of excess late mortality in previously hyperthyroid patients. It is therefore reasonable to assume that in some hyperthyroid patients bone density does not completely return to normal after antithyroid treatment.