As mentioned, K is more to make sure the calcium absorbed as a result of vitamin D can be properly put away instead of hanging around in the arteries.

Magnesium is very important cofactor for metabolism of Vitamin D (and many other things, it’s a cofactor involved with hundreds of enzymes and such), which people are also generally low on.

I think there may be another big cofactor or two, but they escape my offhand recollection.