Bone metabolism in obesity and weight loss

Abstract

Excess body weight due to obesity has traditionally been considered to have a positive effect on bone; however, more recent findings suggest that bone quality is compromised. Both obesity and caloric restriction increase fracture risk and are regulated by endocrine factors and cytokines that have direct and indirect effects on bone and calcium absorption. Weight reduction will decrease bone mass and mineral density, but this varies by the individual's age, gender, and adiposity. Dietary modifications, exercise, and medications have been shown to attenuate the bone loss associated with weight reduction. Future obesity and weight loss trials would benefit from assessment of key hormones, adipokine and gut peptides that regulate calcium absorption, and bone mineral density and quality by using sensitive techniques in high-risk populations.

Figure 1

Arrows indicate direction of fracture risk at bone sites measured by dual-energy x-ray absorptiometry showing axial (lumbar spine and hip) and peripheral sites (humerus, radius, and tibia/ankle) due to increased body mass index (obesity). ^*Higher humerus fracture due to obesity is found in women but not in men (32, 58, 78, 119, 134).

Figure 2

Mechanisms leading to bone loss due to caloric restriction (CR) and weight reduction. 25OHD, 25 hydroxyvitamin D; GIP, gastric inhibitory polypeptide; GLP, glucagon-like peptide; IL-6, interleukin 6; PTH, parathyroid hormone.