Women with vitamin D deficiency were found to have a 43% higher risk of developing MS than those who had adequate levels, found the research team, a collaboration between the Harvard T.H. Chan School of Public Health, Boston and the University of Turku, Finland.
Vitamin D deficient subjects were also 27% more likely to develop MS than those with insufficient vitamin D.
Deficiency and insufficiency were defined as serum vitamin D levels of less than 30 nanomoles/ litre (mol/l) and 30-49 nmol/l respectively.
“These results directly support vitamin D deficiency as a risk factor for MS and strengthen the rationale for broad public health interventions to improve vitamin D levels,” said lead author Kassandra Munger, Sc.D.
The findings of this prospective case-control study are consistent with previous observational research. Nevertheless, intervention trial evidence is lacking and public health authorities have historically been reluctant to adopt supplementation as policy without evidence from randomised controlled trials (RCTs).
An implication for public health policy?
Designing an effective RCT may also be challenging as the authors acknowledge the difficulty of recommending the timing for any supplementation. Clear evidence exists that low maternal vitamin D levels during pregnancy and deficiency in infants significantly heighten the risk of subsequent MS in later life.
Furthermore, the issue of giving a placebo to subjects who have vitamin D deficiency raises an ethical question in any potential intervention.
A 2016 study, which used Mendelian randomisation, perhaps provides the closest thing to firm evidence for a causal effect of vitamin D deficiency on MS.
It is also possible that maintaining adequate vitamin D status over the long-term is the key. Even if changes in public health policy on vitamin D cannot be justified on MS risk reduction alone, “striving to achieve vitamin D sufficiency over the course of a person's life will likely have multiple health benefits," advocates Munger.
The study findings merit further investigation, Munger argues. Given the relatively low cost of supplementation and other health benefits of adequate vitamin D status, there appears little downside to the researchers’ suggestion that public health interventions should be adopted.
“Our results further support and extend those of previous prospective studies of vitamin D levels in young adults and risk of MS, and suggests that many individuals are exposed to an increased MS risk that could be reduced by broad population-based programs to prevent vitamin D deficiency.”
Published online ahead of print. DOI: 10.1212/WNL.0000000000004489
“25-Hydroxyvitamin D deficiency and risk of MS among women in the Finnish Maternity Cohort”
Authors: Kassandra L. Munger, Alberto Ascherio et al