A lot of nutrition research has focused on each member of the four- some individually, ignoring the fact that they interact. It is quite possible you are deficient in all of them, but you will get into trouble if you supplement some of them without tending to the others. It’s like listening only to the violin part to figure out why a symphony is beautiful. You’re going to need all four vitamins at the right levels, working together. D and A, in particular, work together in harmony. It doesn’t make sense to take them separately except in special cases. That is why we lump the four of them together as a single nutritional unit, Vitamin DAKE™