Author: Dr. Stephen Chaney
A new study (Mokry et al, PLOS Medicine, DOI: 10.1371/journal.pmed.1001866, August 25, 2015) suggests that people who are genetically prone to low vitamin D levels are at increased risk of developing multiple sclerosis (MS). To understand the importance of this study and what it means for us, we need to first review what is already known about vitamin D and multiple sclerosis.
- MS is an autoimmune disease in which the immune system attacks the myelin sheath that coats our nerves. Conceptually, that’s the equivalent of a fraying cord on a lamp. Eventually, the cord is going to start shorting out and the lamp won’t work very well. On a very basic level MS is similar. As our myelin sheath is damaged over time, our nervous system starts working less well.
- The earliest evidence that vitamin D status might be associated with MS was the observation that the prevalence of MS was highest for people who lived in northern regions with little exposure to sunlight.
- Numerous studies since then have shown that MS patients generally have lower 25-hydroxy vitamin D levels in their blood.
These studies clearly show an association between low vitamin D status and MS, but association does not prove causation. There are two limitations of association studies that significantly reduce their predictive value – reverse causation and confounding factors.Those are both somewhat highfalutin scientific terms, so let me put them in plain English – and in terms that are relevant to our discussion of vitamin D status and MS.
Reverse causation simple means that the MS might have caused low vitamin D status. For example, individuals with MS might spend less time outdoors because of their physical limitations. That would result in less sun exposure, which would decrease their blood levels of 25-hydroxy vitamin D.
A confounding factor would be something else that increased the risk for MS and happened to be associated with low vitamin D status. Suppose, for example, that exercise decreased the risk of MS. People who spend most of their time inside in front of a TV or computer screen would have low levels of exercise and low sun exposure. If it was the lack of exercise rather than the low vitamin D status that actually predisposed to MS, lack of exercise would be a confounding factor for any clinical study comparing vitamin D status with risk of developing MS.
What Can Genetics Tell Us About The Relationship Between Vitamin D and Multiple Sclerosis?
The authors of this study had previously identified mutations in 4 genes that decrease blood levels of 25-hydroxy vitamin D (the most commonly used measure of vitamin D status). In this study(Mokry et al, PLOS Medicine, DOI: 10.1371/journal.pmed.1001866, August 25, 2015)they analyzed the frequency of those genetic mutations in 14,498 MS cases compared with 24,091 healthy controls. Their study showed:
- Genetic mutations that decrease 25-hydroxy vitamin D levels are associated with a significant increase in the risk of developing MS.
- Based on the relationship of those mutations with 25-hydroxy vitamin D levels, they calculated that every 50% increase in 25-hydroxy vitamin D levels was associated with a 50% decreased risk of developing MS.
This was a very large, well designed study. It has some limitations of its own, but because it used a genetic approach it largely avoids the concern about reverse causation and confounding factors. In short, this study strongly supports the conclusion from previous studies that low vitamin D status significantly increases the risk of developing MS.
The authors concluded “The identification of vitamin D as a causal susceptibility factor for MS may have important public health implications, since vitamin D insufficiency is common, and vitamin D supplementation is both relatively safe and cost effective.”
Is Vitamin D Supplementation Effective In Preventing And Treating MS?
The authors of the study also concluded “These findings provide the rationale for further investigating the therapeutic benefits of vitamin D supplementation in preventing the onset and progression of MS.”
While more studies are still needed, the Nurses’ Health Study (Munger et al, Neurology, 62: 60-65, 2004) provides pretty convincing evidence that vitamin D supplementation can prevent the onset of MS. That study followed 187,563 nurses for at least 4 years, during which time 173 of them developed MS. The study showed that supplementation with 400 IU/day of vitamin D reduced the risk of developing MS by 40%.
The efficacy of vitamin D supplementation in preventing the progression of MS is much less well established. Several studies have shown that low vitamin D status is associated with higher levels MS relapse and more rapid progression of MS symptoms.However, studies of vitamin D supplementation conducted to date have been too small and too short in duration to be definitive.
What Is The Significance Of This Study?
On one hand MS is a very rare disease, affecting around 0.1% of the adult population. On the other hand, it is a debilitating disease. If something as simple as assuring adequate vitamin D status can reduce the risk of developing MS by 40-50%, it is an important public health measure, especially since 40% of the US population has insufficient blood levels of vitamin D (Looker et al, American Journal of Clinical Nutrition, 88: 1519-1527, 2008).
What Does This Study Mean For You?
What does this study mean for you and me? We already know that adequate vitamin D status is essential for building strong bones, and there is pretty good evidence that adequate vitamin D status is important for a strong immune system. Now we can add autoimmune diseases to the list. It is pretty clear that adequate vitamin D status is important for preventing MS. It may help prevent other autoimmune diseases as well.
One interesting wrinkle for MS is that it may be vitally important to assure adequate vitamin D in our younger years. Studies looking at people who grow up in northern latitudes and then move south and vice versa suggest that the risk of developing MS is much more strongly associated with sun exposure during the first 10-15 years of life than with sun exposure later in life.
It is, therefore, not just important that we assure adequate vitamin D status for ourselves. It may be even more important that we assure that our kids and grandkids have adequate vitamin D status.
The problem is that in today’s world we are told to slather industrial strength sunscreen on ourselves from head to foot before we leave the house and very few foods in nature provide significant amounts of vitamin D, so most of us rely primarily on vitamin D fortified dairy products and supplements to assure adequate intake of vitamin D. Click here for the latest RDA recommendations for vitamin D intake.
Some people do appear to need greater than RDA levels of vitamin D because they don’t metabolize vitamin D efficiently. They can have adequate intake of vitamin D, but their blood levels of 25-hydroxy vitamin D are low. I recommend that you ask your doctor to check your 25-hydroxy vitamin D levels at your next physical. If they are low, work out a vitamin D supplementation regimen with your doctor to bring your 25-hydroxy vitamin D levels into the optimal range.
The Bottom Line
- A recent study showed that genetic mutations which decrease 25-hydroxy vitamin D levels are associated with a significantly increased risk of developing MS. Based on the relationship of those mutations with 25-hydroxy vitamin D levels, the investigators calculated that every 50% increase in 25-hydroxy vitamin D levels was associated with a 50% decreased risk of developing MS. This study strongly supports the conclusion from previous studies that low vitamin D status significantly increases the risk of developing MS.
- An earlier Nurses’ Health Study has shown that supplementation with 400 IU/day of vitamin D decreases the risk of developing MS by 40%.
- The authors of the most recent study concluded “The identification of vitamin D as a causal susceptibility factor for MS may have important public health implications, since vitamin D insufficiency is common, and vitamin D supplementation is both relatively safe and cost effective.” I agree.
- While MS is a very rare disease, it can be devastating. This alone, is a good enough reason to be sure that you maintain adequate vitamin D status.
- There is evidence that vitamin D status in our childhood years may be more important than our vitamin D status in later years for determining our risk of developing MS. It is, therefore, not just important that we assure adequate vitamin D status for ourselves. It may be even more important that we assure that our kids and grandkids have adequate vitamin D status.
- While these and other studies demonstrate the health benefits of maintaining adequate vitamin D status, many Americans don’t do a good job of it. Government surveys show that 40% of Americans are deficient in vitamin D. That’s because we are continually being advised to slather on industrial strength sunscreen before we leave the house, and most naturally occurring foods are relatively poor sources of vitamin D.
- While the evidence that vitamin D supplementation is effective for preventing MS is strong, evidence that vitamin D supplementation can slow the progression of MS is inconclusive at present. More and better studies are needed before we will have a definitive answer to this question.
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.