It is difficult to be the devil’s advocate, the role of Caroline Papeix and Catherine Lubetzki, since the evidence, admittedly circumstantial and inferential, suggests that a) vitamin D in large doses is a potent immune modulator 1–4 and that ab) vitamin D deficiency is the major environmental factor in both susceptibility to, and severity of, multiple sclerosis. The studies of the prevalence gradient by latitude of multiple sclerosis and clinically isolated syndrome along east Australia, and in New Zealand are some of the many indirect sources of evidence to support this hypothesis. 5–7

If the debate question was framed as “Would I prescribe vitamin D 10,000 units to a patient with clinically isolated syndrome and an abnormal MRI scan?”, then the answer is, of course,“No”. I agree with the antagonists in this debate that phase 3 trial data are needed before using vitamin D as a therapeutic agent. However, those trial data will take at least another 2-3 years to collect. Thus, while waiting for that proof, if I, or my children, developed a clinically isolated syndrome with an abnormal MRI scan, then I would have no hesitation in prescribing vitamin D in that dose for them.