Assessment of evidence for a protective role of vitamin D in multiple sclerosis.

Evidence for a role of vitamin D insufficiency in determining risk in Multiple Sclerosis (MS) is supported by studies in both pediatric- and adult-onset patients. The potential role of vitamin D in modulating MS disease activity is an area of active clinical trials research, and the possibility of primary disease prevention with vitamin D supplementation in early life is an emerging concept. With Sir Austin Bradford Hill's criteria as a framework, the present review assesses the evidence for a causal relationship between vitamin D insufficiency and the pathobiology of MS, and discusses rationale for future clinical trials with vitamin D.