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| Figure 1: Obesity is an important criterion in the pathogenesis of type 2 diabetes (solid arrows). Vitamin D deficiency is an important feature of obesity mostly due to the storage of 25OHD vitamin in adipose tissue because of its lipophilic properties, causing, in turn, a compensatory increase in PTH (bold arrows). The decrease in 25OHD levels may occur through several mechanisms, resulting in worsening of insulin resistance and secretion and augmenting the risk of developing diabetes. Furthermore, hypo-vitaminosis D may increase insulin resistance indirectly, through the compensatory indirectly, through the compensatory increase in PTH levels. In addition, hypo-vitaminosis D-induced secondary hyperparathyroidism has been shown to inhibit insulin synthesis and secretion from β-cells and reduce insulin sensitivity (dotted arrows). Solid and bold arrows indicate cause and effect relationships; dotted ones indicate not firmly established evidence. |
