India in the past two decades witnessed a dramatic epidemiological transition from
infectious, diseases of undernutrition, and maternal and childhood diseases to
noncommunicable diseases (NCDs). These diseases mainly include cardiovascular
diseases (CVD), cancers, respiratory diseases, diabetes, skeletal disorders 1 .
Amongst these diseases, osteoporosis, a disease of bone and CVD constitute a
considerable burden of NCD as these two share common risk factors and often
occur simultaneously. A need therefore exists to investigate the link between these
seemingly unrelated diseases of bone and cardiovascular systems.
1. Bone biology
Bone is a vascularized and metabolically active connective tissue that exerts
numerous functions in the body such as provision of mechanical support to the body
and protection of internal vital organs such as brain, spinal cord and heart. It is a
storehouse for calcium and phosphorous, the major site for metabolic pathways
associated with mineral homeostasis and provide site for ligaments and muscles
attachment. The process of skeletal development during early stages of life is called
bone modeling which involves the deposition of mineralized tissue at
developmentally determined sites. Once skeleton achieves maturity, the processes
of bone resorption and bone formation equally balance each other in a healthy
skeleton. This continuous process, termed as bone remodelling is essential for the
maintenance of bone structure and its strength 2 . It involves replacement of
old/damaged bone through the combined action of the osteoclasts, the bone
resorbing cells and osteoblasts, the bone forming cells. Bone remodelling cycle
comprises of three phases: 1) initiation of bone resorption by osteoclasts 2) the
transition (or reversal period) from resorption to new bone formation and 3) bone
formation by osteoblasts3, 4. This remodelling is necessary to maintain the structural
integrity of the skeleton. Normal bone remodelling cycle involves bone resorption
and formation in a co-ordinated fashion.
