Relationship of body adipose tissue distribution with vitamin D and bone metabolism indices in patients with type 2 diabetes mellitus

Currently, there is growing interest in understanding relationships among vitamin D, bone metabolism indicators, and diabetes. Numerous studies have highlighted vitamin D deficiency as a risk factor not only for obesity but also for fluctuations in blood glucose levels and insulin resistance. Human adipose tissue is categorized into visceral fat and subcutaneous fat based on its distribution. Although visceral fat comprises a smaller proportion compared to subcutaneous fat, it is considered to have a much more significant impact on various diseases such as obesity and diabetes. However, precise relationships among different adipose tissues, vitamin D deficiency, and bone metabolism-related indicators remain unclear. Furthermore, it is uncertain whether the effects of vitamin D on bone metabolism differ between individuals with normal visceral fat and those with excessive visceral fat. Moreover, to date, most research examining the relationship between vitamin D and fat distribution has focused specifically on the vitamin D precursor produced by the liver, 25(OH)D. Importantly, determining 25(OH)D levels constitutes an indirect measure of vitamin D enumerating an inactive intermediate in the pathway generating the active form of vitamin D, 1,25(OH)2D3. As such, this study includes 1,25(OH)2D3 in the research indicators, providing a more comprehensive and direct understanding of the relationships among vitamin D, adipose tissue distribution, and bone metabolism. In addition, this study aims to investigate not only the impact of normal visceral fat and excessive visceral fat on bone metabolism indicators but also to compare the differences between subcutaneous fat and visceral fat contributing to bone metabolism.