An Overview of Different Vitamin D Compounds in the Setting of Adiposity

Abstract

A large body of research shows an association between higher body weight and low vitamin D status, as assessed using serum 25-hydroxyvitamin D concentrations. Vitamin D can be metabolised in adipose tissue and has been reported to influence gene expression and modulate inflammation and adipose tissue metabolism in vitro. However, the exact metabolism of vitamin D in adipose tissue is currently unknown. White adipose tissue expresses the vitamin D receptor and hydroxylase enzymes, substantially involved in vitamin D metabolism and efficacy. The distribution and concentrations of the generated vitamin D compounds in adipose tissue, however, are largely unknown. Closing this knowledge gap could help to understand whether the different vitamin D compounds have specific health effects in the setting of adiposity. This review summarises the current evidence for a role of vitamin D in adipose tissue and discusses options to accurately measure vitamin D compounds in adipose tissue using liquid chromatography tandem mass spectrometry (LC/MS-MS).

Keywords: 25-hydroxyvitamin D; C3 epimer; inflammation; metabolic health; obesity; overweight.

Figure 1

Schematic overview of vitamin D metabolism in humans. ↑ indicates an increase, ↓ indicates a decrease. Abbreviations: ultraviolet light short wavelength (UVB); calcidiol (25(OH)D); calcitriol (1,25(OH)₂D); retinoid X receptor (RXR); vitamin D receptor (VDR); vitamin D response element (VDRE); parathyroid hormone (PTH); calcium (Ca).

Figure 2

Depiction of the relation between vitamin D status and white adipose tissue (WAT) mass in people with higher body weight. The response to vitamin D supplementation is altered in people with higher body weight, and an increased BMI is associated with lower serum 25(OH)D levels. In addition, white adipocytes express the VDR and hydroxylase enzymes. Vitamin D can have a beneficial effect on processes in WAT; however, it is unknown whether these effects are mediated by specific vitamin D compounds. ↑ indicates an increase, ↓ indicates a decrease. Abbreviations: BMI, body mass index; VDR, vitamin D receptor; WAT, white adipose tissue; 25(OH)D, 25-hydroxyvitamin D.