ReviewObesity is a risk factor for fracture in children but is protective against fracture in adults: A paradox

With the rise in obesity worldwide, an important debate has developed as to whether excess fat has a detrimental or protective effect on skeletal health in children and adults. Obese children appear to be over represented in fracture groups and recent evidence suggests that fat may be detrimental to bone accrual in children, although this effect may be confined to adolescence during rapid skeletal growth. Fat induced alterations in hormonal factors and cytokines during growth may play a pivotal role in disturbing bone accrual. In contrast, the widely accepted opinion is that fat appears to be protective of bone in adults and minimises bone loss in postmenopausal women. Recent evidence suggests that in adults, site specific fat depots may exert differing effects on bone (with visceral fat acting as a pathogenic fat depot and subcutaneous fat exerting protective effects), and that the effects of fat mass on bone and fracture risk may vary by skeletal site; obesity protects against hip and vertebral fractures but is a risk factor for fractures of the humerus and ankle. The incidence of fracture during adolescence is rising and osteoporosis remains a considerable health burden in older adults. Understanding the effects of fat mass on bone during growth and early adulthood is vital in informing future health strategies and pharmacotherapies to optimise peak bone mass and prevent fracture.This article is part of a Special Issue entitled: Interactions Between Bone, Adipose Tissue and Metabolism.

Research Highlights► Obesity may be associated with a low bone mass in obese children particularly in adolescence. ► In adults obesity is protective of bone although recent evidence suggests visceral fat may be harmful to bone. ► Alterations in fat derived hormones may be key to obesity-related-changes in bone. ► There is a paucity longitudinal studies examining the changing relationship between fat and bone with skeletal growth and development. ► New imaging techniques may advance our understanding of how fat interacts with bone.