Obesity, osteoporosis and bone metabolism.

Obesity and osteoporosis have become major global health problems over the last decades as their prevalence is increasing. The interaction between obesity and bone metabolism is complex and not fully understood. Historically, obesity was thought to be protective against osteoporosis;however, several studies have challenged this belief. Even though the majority of the studies suggest that obesity has a favourable effect on bone density, it is unclear what the effect of obesity is on skeletal microarchitecture. Additionally, the effects of obesity on skeletal strength might be site-dependent as obese individuals are at higher risk of certain fractures. Several mechanical, biochemical and hormonal mechanisms have been proposed to explain the association between the adipose tissue and bone. Mechanical loading has positive effects on bone health, but this may not suffice in obesity. Low-grade systemic inflammation is probably harmful to the bone and increased bone marrow adipogenesis may lead to decreased bone mass in obese individuals. Finally, visceral abdominal fat may exert different actions to the bone compared with the subcutaneous fat. Achieving a better understanding of the association between adipose and bone tissue may help to identify new molecular therapeutic targets that will promote osteoblastic activity and/or inhibit adipogenesis and osteoclastic activity.