The bioactive form of vitamin D is also known as calcitirol. It's a hormone that has its vital role in metabolism of calcium and phosphorus in the body. It also has a vital role in mineralization of bones. In most recent studies it has been proved that vitamin D is present in a variety of cells in human body and also that this hormone has far more importance than that.
Structure and Synthesis
Vitamin D Supplement
This is a vitamin synthesized in human body by direct exposure to sunlight. Thus it's not a true vitamin as the individuals having enough exposure to sun light don't need the supplements for this but there are dietary sources also like egg, yolk, and oil etc. the vitamin D available in plant form is also known as D2 or esgosterol. However the regular exposure and foods are not enough to fulfill daily need in some conditions so the supplements must also be used. Vitamin d, either D1or D2 have not any biological activity unless it is converted its active form 1,25-dihydroxycholecalciferol.this occurs in two steps first step is within the liver from where it is sent to the kidney to covert it into its biological active form.
The Vitamin D Receptor and its metabolism
The active form of vitamin binds with its receptors to induce gene expression. Like other hormones vitamin d has two binding sites that have hormone binding and DNA binding domains. It forms a complex with retinoid x receptor. This binding cause transcription but cases are known when it prohibits transcription.
Vitamin D metabolism and calcium absorption
Vitamin d along with parathyroid hormone and calcitonin are the three main effectors on calcium and phosphorus homeostasis. The vitamin D3 is subjected to metabolic conversion to its biological active form in accordance to initiation of its physiologic responses in the intestine and skeletal system. The production of vitamin D3 is directly linked with the pH levels and calcium need of that human being.
Vitamin D metabolism
Vitamin D is well known hormone to be involved in bone growth and mineral metabolism. Its most important effects are in absorption of calcium although it also facilitates absorption of phosphate and magnesium. In absence of vitamin D dietary calcium will be fruit less so the vitamin D metabolism is also necessary for calcium and bones. There are numerous effects of vitamin D on bone. It induces the expression of osteaocalxin and suppresses synthesis of type 1 collagen. The crucial effect of vitamin D on bone is to provide proper balance of calcium and phosphorus to support mineralization.