Vitamin D role in maintaining good health and defeating disease

Vitamin D is a fat-soluble secosteroid that exists in two forms: vitamin D2 and vitamin D3. Plants and fungi produce vitamin D2 from ergosterol, while human skin produces vitamin D3 from 7-dehydrocholesterol [7-DHC] when exposed to UVB radiation from the sun. Vitamin D role in maintaining good health and defeating disease. Vitamin D3 is transported to the liver, where it is converted by CYP2R1 to 25-hydroxyvitamin D3 [25(OH)D3], which is the main circulating form of vitamin D3. Finally, 25(OH)D3 is converted to its active form, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], in the kidney by CYP27B1.

The primary function of 1,25(OH)2D3 is to maintain normal calcium levels and bone development by regulating phosphocalcium metabolism. Additionally, vitamin D may have non-skeletal effects due to the discovery of vitamin D receptors (VDRs) in a variety of tissues, including the prostate, brain, breast, pancreas, colon, and immune cells.

1,25(OH)2D3 can play a role in the immune function and regulation of cell proliferation and differentiation in a variety of cell lineages (lymphocytes, endothelial cells, osteoblasts, and keratinocytes). In addition, it has been shown that 1,25(OH)2D3 can influence the regenerative capacity of intestinal stem cells and accelerate intestinal repair; vitamin D is associated with diabetic retinopathy and plays an important role in maintaining eye health; vitamin D also influences anti-angiogenic processes by regulating aspects of the cell cycle and can alter the risk of cardiometabolic outcomes, including hypertension, cardiovascular disease, and diabetes mellitus. Vitamin D also inhibits the replication of Mycobacterium tuberculosis in vitro, showing promise for the treatment of tuberculosis.

The vitamin D and health and disease — Figure Vitamin D exerts its biological effects through the vitamin D receptor (VDR)
**Note:** 1,25(OH)D3 can quickly diffuse through cell membranes and bind to VDR. VDR forms heterodimers with the retinoid X receptor (RXR) after binding to the ligand, moving into the nucleus where it binds to vitamin D response elements (VDREs) to regulate gene transcription. The VDR also controls the transcription of genes by interacting with other nuclear receptors. The functions of vitamin D include growth and bone mineralization, immune function regulation, insulin secretion regulation, cell proliferation control, cell differentiation stimulation, apoptosis induction, phosphor calcium homeostasis regulation, and muscle calcium transport regulation.

Holick, M. F. (2017). The vitamin D deficiency pandemic: Approaches for diagnosis, treatment and prevention. Reviews in Endocrine and Metabolic Disorders, 18, 153-165.
Delrue, C., & Speeckaert, M. M. (2023). Vitamin D and Vitamin D-Binding Protein in Health and Disease. International Journal of Molecular Sciences, 24(5), 4642. [Link]