The first observational study has been published showing decreasing relapse rates in people with MS taking vitamin D supplements according to how much these supplements raised their vitamin D level.

Previously, a number of observational studies of groups of people with MS have shown that the higher the blood vitamin D level, the lower the relapse rate.

However these studies were in people who were not being systematically supplemented with vitamin D. Many experts argued that it was actually the illness being active that stopped these people getting outdoors, and hence their vitamin D levels went down, rather than the vitamin D reducing the relapse rate.

This phenomenon is called reverse causality, and is often mentioned in this type of population study. The current study looked at 156 people with relapsing-remitting MS in Paris, France, divided into two groups, one that started on disease-modifying drugs before starting vitamin D supplements, and the other where the two treatments were started at the same time.

The dose of vitamin D used averaged out to be a little over 3,000IU a day, although it was given as a periodic megadose rather than a daily dose. The researchers noted that this level of supplementation with vitamin D should now reasonably be considered as ‘routine care’.

They also noted that their aim was to have participants reach a blood level of 75-200nmol/L, that is to be in the normal range. In this study, the average blood level of vitamin D went up from 49nmol/L (indicating the group was deficient at the outset) to 110nmol/L.

It should be noted that the dose of supplementation is small compared to what we at OMS have long recommended, and that the final blood level is also low compared to what we recommend as optimal (150nmol/L or above).

The results were highly statistically significant, with every 10nmol/L rise in vitamin D level reducing relapse rate by 13.7%. It should be noted that no calcium supplements were provided in this study, and that calcium levels in all people remained normal throughout the period of supplementation.

The researchers found no additional reduction in relapse rate above a blood level of 110nmol/L. However, the methodology for this study was not ideal for determining the optimal blood level; the researchers only supplemented people with levels lower than 100nmol/L.

Determining the optimal level exactly will need to wait for randomised controlled trials of supplementation using different doses, achieving higher blood levels.

In the meantime, this study gives strong support for regular vitamin D supplementation for people with MS, and suggests that vitamin D blood levels commonly recommended as adequate by doctors of achieving a ‘normal’ (50-75nmol/L) level are not optimal for people with MS.

Higher levels than this are likely to result in significant reductions in relapse rates and disease activity.