Adipose tissue and the skeleton - new insights into pathogenesis of osteoporosis

Osteoporosis and obesity are chronic conditions with increasing prevalence rates. For a long time, they were considered separate en­ tities rarely found in a single individual. Recently, however, there has been growing evidence from clinical studies suggesting impor­ tant interactions between adipose tissue and the skeleton. Adipose tissue may influence bone remodeling by three mechanisms: (1) se­ cretion of endocrine cytokines and growth factors directly targeting the bone, (2) production of adipokines affecting the CNS and thus changing sympathetic impulses into the bone, and (3) paracrine effects on the adjacent bone cells (adipocytes in bone marrow). Excess subcutaneous fat contributes to maintaining cortical bone mass. On the other side, visceral fat gain is associated with a loss in trabe­ cular bone mass. Individuals with metabolic syndrome, and thus with excess visceral fat, are at a higher risk of fractures despite their normal BMD values. Whether obesity is a risk factor for osteoporosis remains an open question.

Keywords: bone, fat, obesity, osteoporosis, osteocalcin, insulin