FSH versus estrogen: who's guilty of breaking bones?

Bone loss after menopause or gonadectomy has been attributed to the drop in estrogen levels. A recent paper (Sun et al, 2006) challenges this view by showing that the pituitary hormone FSH, previously thought to target only the gonads, also acts on osteoclasts to activate bone resorption. In conjunction with genetic studies, these data raise the possibility that FSH, independent of estrogen, causes hypogonadal bone loss.