Vitamin D: the mechanism, the molecule, the screenplay

What's hip loyal biologists? (obviously not this blog) Today on my quest for knowledge of our biological universe, I came across the fascinating, fat soluble steroid known as Vitamin D. The D2 and D3 molecules to be more precise. You've probably heard of rickets, and a bit about how the sun stimulates Vitamin D's release in our bodies. If you're an introvert obsessed with science and video games like me, then you know where I'm coming from. Vitamin D is vital in our bodies to enhance absorption of key minerals in the intestinal system, like calcium, iron or zinc. These elements are used to construct and maintain our skeletal system, so that's why if children develop a vitamin D deficiency, their bones can become elongated and deformed, because they cannot absorb enough calcium or phosphorous for proper skeletal development. Although this mostly occurs in countries with a high prevalence of genetic disorders such as pseudovitamin D deficiency rickets. Vitamin D is marketed on the internet as a miracle cure for conditions like cancer, heart disease, depression and autoimmune disease, despite the fact that no clinical trials have proven this claim. In fact they mostly say Vitamin D has a negligible impact on such conditions. The D3 vitamin molecule is produced in the skin, when exposed to UV light, from another molecule called 7-dehydrocholesterol. This precursor of vitamin D3 is produced in relatively large quantities, in fact 10,000 to 20,000 IU of vitamin D are produced in 30 minutes of whole-body exposure, in the skin of most vertebrate animals. 7-dehydrocholesterol is converted into D3 by UVB rays between 270 and 300 nm, but occasionally an equilibrium can form in the skin, in which vitamin D degrades as fast as it is synthesised. But that's not the end of vitamin D's journey in the body. In the liver it is converted into a prohormone (precursor to a hormone) known as calcidiol, and then it is converted yet again in the kidneys, but this time to its biologically active form; calcitriol (a bit like phytochromes in plants for you botanists out there) . Calcitriol binds to the vitamin D-binding protein, which transports it to vitamin D-rerceptors (VDRs) on the surface of target cells. Here's where it gets really good. The VDRs bound to vitamin D will act as transcription factors, promoting expression of transport proteins like TRPV6 (catchy right?) within cells,  which are involved in absorption of calcium in the immune system. So what have we learnt? For one thing the proteins and receptors involved with Vitamin D have incredibly uncreative names. But on a more serious note, sunlight is essential to skeletal health, so maybe we should embark on adventures is the great outdoors more frequently! I'm such a hypocrite...