vitamin D deficiency is most likely a clever scam funded by the supplements industry. Theres ZERO evolutionary reason for humans to suddenly depend on UV exposure and at the same time get our skin destroyed, become prone to cancer etc.
proper amounts of calcium and phosphorus + vitamin K is probably whats needed for great bone development. an optimal hormone balance is also necessary (and probably more important) for great skin as mentioned earlier.http://mpkb.org/home/diseases/rickets
Rickets (osteomalacia) is a softening of the bones that leads to fractures and deformity. The majority of cases of rickets occur among children in developing countries who suffer from severe malnutrition. The disease is cited as a primary reason for consuming vitamin D regularly even though research has demonstrated that rickets is not caused by vitamin D deficiency but by hypophosphatemia.
The USDA's conclusion (mentioned in the previous section) is consistent with common sense. It's hard to imagine that children in Africa, who get copious amounts of sunlight, which catalyzes vitamin D production, even in those with dark skin, are suffering from a disease caused by vitamin D deficiency.
If a child with rickets is severely deficient in vitamin D, as well as in calcium and phosphorous, administering a small amount of vitamin D (which will be immediately converted into 1,25-D) can help by allowing the Vitamin D Receptor to turn on genes that affect the absorption of calcium. This probably explains why in the early 19th century, some children given high does of vitamin D were said to be cured from rickets.
However, if supplementation is continued, the level of the precursor form of vitamin D (25-D) in the body will soon reach the point at which it becomes immunosuppressive. With the negative effects of this situation in mind, it makes much more sense that patients low in calcium should simply be given extra calcium, which can remedy the situation without the need for vitamin D.