Vitamin D deficiency: An independent risk-factor or a marker of poor health

In the last few decades there has been much interest on extra-skeletal effects of vitamin D deficiency along with considerable expectations that vitamin D or its derivatives could provide new therapeutic approach to a wide variety of diseases. The most robust data on the beneficiary effects of vitamin D in extra-skeletal body systems derive from basic science and observational/epidemiological studies. Interventional studies are few and much less conclusive. The current review provides an overview on the available data on extra-skeletal effects of vitamin D deficiency and available interventional studies, and presents the complexity of dissecting-out the role of vitamin D in given disease conditions. A paradigm is presented which attempts to reconcile between the impressive effects of vitamin D in extra-skeletal systems in basic research and epidemiological studies and the inconclusive results of the available controlled interventional studies. Available data support the notion that vitamin D deficiency is both an independent risk factor, and a non-specific marker of poor health.