Vitamin D Council Glossary

# A B C D E F G H I J–K L M N O P R S T U V
Vitamin A
Fat-soluble vitamin which helps with normal functioning of the mucus membranes of the eye and respiratory tract, and the formation of visual pigments in the eye. It is also essential for normal tissue growth and differentiation. see retinol and beta-carotene.
Vitamin D
A prohormone that behaves similar to a steroid in that it binds to a receptor and has a regulatory effect on gene expression. Vitamin D plays an important role in: the maintenance of several organ systems, bone formation and mineralization, and the control of calcium and phosphorus metabolism. Vitamin D also performs immunosuppressive and anti-tumor functions and is vital for the maintenance of the blood/brain barrier. The term vitamin D also refers to vitamin D metabolites and synthetically-derived vitamin D analogues.
Different forms of vitamin D:
Vitamin D1: molecular compound of ergocalciferol and lumisterol (1:1 ratio).
Vitamin D2: ergocalciferol or calciferol (made from ergosterol).
Vitamin D3: cholecalciferol (made from 7-dehydrocholesterol). Vitamin D3 is real vitamin D. All other compounds are either metabolic products or chemical modifications.
Vitamin D4: dihydrotachysterol 22,23-dihydroergocalciferol.
Vitamin D5: sitocalciferol (made from 7-dehydrositosterol).
Vitamin D 24-Hydroxylase
see CYP24A1.
Vitamin D Analogue
Also called vitamin D receptor agonist. Synthetic compound based upon variation of one of the naturally-occurring vitamin D metabolites. Vitamin D analogues have been known to adversely affect calcium homeostasis, causing hypercalcaemia.
Vitamin D Binding Protein (DBP)
Carries vitamin D3 and its metabolites to their various target organs. Plays a key role in the operation of the vitamin D endocrine system.
Vitamin D Endocrine System
The Vitamin D Endocrine System has the ability to generate biological responses in over 30 target tissues through nuclear receptor (nVDR) regulation of gene transcription and nongenomic pathways. Functions include calcium, electrolyte, and energy homeostasis; lipid metabolism; hair growth cycle and blood pressure regulation; cell differentiation stimulation; cell proliferation inhibition; maintenance of mineral ion homeostasis; preservation of bone density; establishment and maintenance of immunological self-tolerance.
Pathway of Vitamin D Endocrine System:
  1. Photoconversion in the skin of 7-dehydrocholesterol to vitamin D3 (cholecalciferol), or oral supplementation of vitamin D3.
  2. Liver metabolizes vitamin D3 to 25(OH)D3 (calcidiol), the major form of vitamin D circulating in the blood.
  3. Kidney converts 25(OH)D3 to 1a,25(OH)2D3 (calcitriol) for autocrine and paracrine function.
  4. 1a,25(OH)2D3 is transported from kidney to principal endocrine target organs (intestine, parathyroid, kidney, and bone).
  5. 1a,25(OH)2D3 binds to nuclear receptors in dozens of autocrine target organs, generating biological responses.
Vitamin D hypersensitivity
Rare syndrome that occurs when abnormal tissue subvert the kidney's normal regulation of endocrine calcitriol production, causing high blood calcium (hypercalcaemia).
Vitamin D level or vitamin D blood level
see blood calcidiol level.
Vitamin D receptor (VDR)
Intracellular hormone receptor that belongs to the steroid-retinoid-thyroid nuclear receptor gene super-family. VDRs mediate the genomic actions of vitamin D3 and regulate gene expression by binding with vitamin D response elements. Vitamin D receptors have been found to be present on intestinal, bone, liver, kidney, hematopoietic, skin, muscle, heart, pancreas, adrenal, brain, reproductive, lung, pituitary, thyroid, and cartilage tissues as well as on lymphocytes, monocytes, and macrophages, indicating the substantial impact vitamin D has on health and well-being. It is theorized that VDR polymorphisms are associated with the development and progression of cutaneous malignant melanoma.
Vitamin D3 up-regulated protein 1 (VDUP1)
Stress-response gene that is up-regulated by calcitriol in many cells.
Vitamin K
Vitamin K is a fat-soluble vitamin that is essential for the functioning of several proteins involved in blood clotting. One form of vitamin K, vitamin K2, is considered a co-factor of vitamin D in that it helps direct vitamin D to calcify the proper organs and prevents calcification of improper organs.

*These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.