One could write volumes on the *known* actions and interactions of *vitamin* D... on just D binding proteins alone, a book.
The reason magnesium across the skin has become perhaps the best method to bump up magnesium in one's body, is due to a number of *modern* issues such as, nutritionally poor available foods (lacking magnesium), not eating enough greens, and toxic loads never before dealt with - which in turn increases the nutritional mineral needs in most people.