Everybody knows about Vitamin D and that we get it from sun. Did you actually know Vitamin D is in fact a prohormone by itself and in is active form it is a steroid hormone? Vitamin D was misnamed when it was first discovered hundreds of years ago, before we knew where it came from or how it was made. By definition, it is not a vitamin because vitamins are not produced endogenously they must be obtained exogenously from dietary food source. Vitamin D isn't even a nutrient, it comes from the sun, not nutrition.
The history of vitamin D comes from a long way. When the human race was black and exposed to tremendous amount of sun by living near the equator, humans we're black. Having a black skin would have huge amount of melanin which explains the blackness of their skin because they were exposed to the sun on a daily basis and they weren't affected by seasons. As we migrated away from the equator ,therefore reducing our exposure to the sun, natural selection quickly eliminated most of the melanin pigmentation from our skin to compensate for the much weaker levels of UV radiation avaible for making Vitamin D. Today we are passing most of our time indoors and this is why we need Vitamin D supplements of at least 1,000UI per day.
Everyone knows Vitamin D can prevent rickets but it can also prevent 17 type of cancer including pancreatic, kidney, colon/rectal, prostate, lung, ovarian, lymphoma, uterine, multiple myeloma, breast, bladder and it can also improve you immune system function, autoimmune function, inflammation, multiple sclerosis, autism, alergies, preecampsia, type 1 and 2 diabetes, depression, muscle and bone weskness, generalized pain and, like everyone knows osteoporosis.
Why do we don't know all the benefits rather than only know it helps with calcium and phosphorus absoption? Only university and some hospital affiliated researchers, with limited budgets, have any interest in exploring the health benefits of Vitamin D. And even when they demonstrate the amazing benefits of maintaining higher level of Vitamin D, who's gonna market and sell that information? There's no money in it! The researches are all over the internet but the general public won't know about all the benefits since there's no one running expensive prime-time commercials to sell it! Vitamin D is inexpensive and cannot be patented.
Basically, Vitamin D inexpensively promotes health.