Recent improvements in our understanding of physiology have altered the way in which bone is perceived: no longer is it considered as simply the repository of divalent
ions, but rather as a sophisticated endocrine organ with potential extraskeletal effects. Indeed, a number of pathologic conditions involving bone in different ways can now be reconsidered from a bone-centred perspective. For example, in
metabolic bone diseases like
osteoporosis (OP) and
renal osteodystrophy (ROD), the association with a worse cardiovascular outcome can be tentatively explained by the possible derangements of three recently discovered bone
hormones (
osteocalcin,
fibroblast growth factor 23 and sclerostin) and a bone-specific
enzyme (
alkaline phosphatase). Further, in recent years the close link between bone and
inflammation has been better appreciated and a wide range of chronic inflammatory states (from
rheumatoid arthritis to ageing) are being explored to discover the biochemical changes that ultimately lead to bone loss and OP. Also, it has been acknowledged that the concept of the bone-vascular axis may explain, for example, the relationship between bone metabolism and vessel wall diseases like
atherosclerosis and
arteriosclerosis, with potential involvement of a number of
cytokines and metabolic pathways. A very important discovery in bone physiology is the bone marrow (BM) niche, the functional unit where stem cells interact, exchanging signals that impact on their fate as bone-forming cells or immune-competent haematopoietic elements. This new
element of bone physiology has been recognized to be dysfunctional in diabetes (so-called diabetic mobilopathy), with possible clinical implications. In our opinion, ROD, the
metabolic bone disease of renal patients, will in the future probably be identified as a cause of BM niche dysfunction. An integrated view of bone, which includes the BM niche, now seems necessary in order to understand the complex clinical entity of
chronic kidney disease-
mineral and bone disorders and its cardiovascular burden. Bone is thus becoming a recurrently considered paradigm for different inter-organ communications that needs to be considered in patients with complex diseases.