For the past few years, an increasing number of in vitro studies show the association of iron accumulation with bone loss, particularly in postmenopausal women. And body iron accumulation is accurately reflected by levels of serum ferritin in clinic. The levels of serum ferritin among healthy women are about 13-150μg/L, and we give a definition of iron accumulation when serum ferritin range from 500μg/L to 1000 μg/L. How will the bone mineral density change in iron accumulation? The investigators intend to perform this study to explore and establish the relational function and logical function between serum ferritin, bone mineral density and biochemical markers of bone metabolism in Chinese healthy postmenopausal women.