Osteoprotectin (OPG), also known as osteoclast inhibitory factor (OCIF) or tumor necrosis factor receptor superfamily member 11B(TNFRSF11B), is a cytokine receptor that is a member of the tumor necrosis factor receptor superfamily. OPG reduces the production of osteoclasts by inhibiting the differentiation of osteoclast precursors into osteoclasts, and also regulates the absorption of osteoclasts in vitro and in vivo. Recombinant human OPG acts specifically on bone and can increase bone mineral density and volume. Elevated OPG levels have been reported in patients with heart disease and severe mental disorders. In recent years, researchers have speculated that OPG may have a link between bone and cardiovascular disease, specifically associated with increased cardiovascular risk in people with diabetes.