Over the last few decades there have been huge controversies about whether there are widespread vitamin D deficiencies and whether vitamin D supplementation could prevent many chronic illnesses. Dr. Michael Holick claims there is a vitamin D deficiency pandemic. Dr. Holick points to association of vitamin D deficiency with a myriad of acute and chronic illnesses including preeclampsia, childhood dental caries, periodontitis, autoimmune disorders, infectious diseases, cardiovascular disease, deadly cancers, type 2 diabetes and neurological disorders.
However, a umbrella study that addressed meta-analyses that addressed studies where vitamin D supplements were given did not show much effectiveness in terms of outcomes when vitamin D was supplemented.
Dr. Holick is a lot more right than wrong. Taurine is required for calcium homeostasis. See also this paper. See also this paper. With taurine deficiencies calcium homeostasis is upset. With taurine deficiencies individuals can develop severe cases of osteomalacia even where vitamin D levels are normal.
Very unfortunately supplementation with vitamin D alone is not enough to treat these dysregulations of calcium homeostasis. The umbrella study as to the efficacy of vitamin D supplementation alone is also correct. To treat dysregularities in calcium homeostasis due to deficiencies in taurine, L-taurine must be supplemented, calcium hydproxapatite must be supplemented and vitamin D must be supplemented.