Circadian Regulation of Bone

Abstract

The demands of modern society are posing serious effects on our bone health. People are working longer hours, working through the night, getting less sleep, and eating at irregular hours. This is causing more stress and less time to spend outdoors. All of these factors are contributing to circadian disruption “in general” but more importantly to circadian disruption of bone rhythms. Bone metabolism displays circadian variation that is coincident with clock rhythms in bone, with the light/dark cycle and with circulating melatonin levels. Light exposure at night, shift work, and poor quality sleep can lead to weakened bones attributed, in part, to altered clock rhythms in bone and to changes in circulating melatonin and cortisol rhythms in the body. The intent of this review is not to describe bone metabolism “in general” and then to discuss the effect of melatonin in these processes. There are many reviews on this subject matter described throughout the chapter. Rather, the focus of this chapter is to describe clock gene expression and function in bone and how their rhythms impact on osteoblast and osteoclast activity and differentiation and on bone metabolism; and then discuss variables that lead to circadian disruption of bone rhythms and describe ways to maintain healthy bone in a society that continually promotes circadian disruption.