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. 2011 Feb 3;5(2):197–214. doi: 10.1016/j.molonc.2011.01.007

Figure 1.

Figure 1

Vitamin D Metabolism and Biological effects. Sun exposure (UVB) results in photoactivation of 7‐dehydrocholesterol to pro‐D3(cholecalciferol), then heat results in production of Vit D3. Endogenous and dietary Vit D3 along with dietary D2 (ergocalciferol) are metabolized by the liver and kidney to 1,25(OH)2D3 (1,25 dihydrocholecalciferol) via the enzymes 25‐OHase (25‐hydroxylase) and 1αOHase (1α‐hydroxylase) encoded by the genes CYP27A1 and CYP27B1 respectively. 1,25(OH)2D3 has a negative feedback on PTH secretion and it's classical effects are on intestinal absorption and bone mineralization. Many cells have the ability to synthesis 1,25 dihydrocholecalciferol locally, resulting in possible apocrine and paracrine non‐classical effects on a variety of tissue and immune cells. Vitamin D forms a heterodimer with retinoid X receptor and binds to the nuclear vitamin D receptor (VDR) resulting in effects on gene expression.