I found a blog post that makes an interesting argument that some of the studies showing lower Vit. D linked to increased mortality in osteoporosis and autoimmune disease are showing an effect of infection and Vit. D receptor disregulation rather than simple deficiency.

You won't find any research that shows vitamin D + calcium increases bone density above calcium alone. Blood levels of calcium, yes. But not bone density.

Many people with low 25D have high 1,25D which is a product of 25D
That argues against deficiency in some cases. And in favor of infection + occasionally dysregulation of the Vitamin D Receptor resulting in overproduction of
1,25D from 25D (which leads to low levels of 25D, which appears like deficiency)

bacteriality.com/2007/09/15/vitamind/

They say high levels of 25D deactivates the Vitamin D receptor based on molecular modeling, though. That part I question. How much D3 supplementation does it take to maximize cathelidicin production?
I cannot find an answer to that question, and it should be simple.