Fat and Bone: An Odd Couple

Abstract

In this review, we will first discuss the concept of bone strength and introduce how fat at different locations, including the bone marrow, directly or indirectly regulates bone turnover. We will then review the current literature supporting the mechanistic relationship between marrow fat and bone and our understanding of the relationship between body fat, body weight, and bone with emphasis on its hormonal regulation. Finally, we will briefly discuss the importance and challenges of accurately measuring the fat compartments using non-invasive methods. This review highlights the complex relationship between fat and bone and how these new concepts will impact our diagnostic and therapeutic approaches in the very near future.

Keywords: MRI; bone; fat; hormones; imaging; marrow fat; vitamin D.

Figure 1

(A) Depiction of the mid-third of the right femur in a 19-year-old male (the localizer image). (B) Values for % marrow fat (black circles) and cortical bone area (gray diamonds) at all slices along the mid-third of the right femoral shaft and their overall relationship in the same subject [reproduced from Wren et al. (46)].

Figure 2

Conceptual model of the interrelationship between bone, fat, and muscle and the role of vitamin D. An increase in vitamin D should lead to a decrease in muscle fat leading to an increase in muscle strength and a subsequent increase in bone and simultaneous decrease in marrow fat (MF). However, there is also the possibility that increases in vitamin D will also directly lead to an increase in bone.