Conclusion

Although genetic and epidemiological data are interesting, available evidence supporting vitamin D supplementation in MS is still lacking. We believe that vitamin D supplementation should be proposed, as for any drug-based therapy, only when sufficient evidence of efficacy has been gathered. If all MS patients receive vitamin D because “it might be useful, and it is not harmful”, then it will not be possible to demonstrate either efficacy or lack of efficacy. As stated above, however, such late-phase studies face particular methodological challenges. There is a need to improve dietary assessment methods and to take into account key confounders before initiating such late-phase studies.