PTH and hyperinsulinism: At the bone tissue level, insulin physiologically increases osteoblast proliferation and collagen formation and inhibits parathyroid hormone (PTH) action; conversely, the state of hyperinsulinism leads to a decrease of osteoprotegerin (OPG) as well as insulin-like growth factors 1 and 2 and insulin-like growth factor-binding protein 1, increasing bone reabsorption [66,67].