Multiple sclerosis (MS) is a neurological disorder. At its root, is degeneration of the fatty sheaths that surround the nerve fibres in the brain and spinal column. The degeneration of these sheaths (known as myelin sheaths) disrupt neurological function, and can manifest in any number of ways including physical disability and impaired brain function. It’s been noted that populations further from the equator have increased risk of MS compared to those closer to it. Perhaps not surprisingly, these have led some to investigate the role of vitamin D and sunlight in relative protection from MS.
It is generally believed that MS is ‘autoimmune’ in nature – which means it’s caused by the body’s immune system reacting against its own tissues (in this case, the myelin sheaths). There has been quite a lot of evidence which suggests that vitamin D has the capacity to modulate the immune system in a way that can dampen any tendency to autoimmunity .
However, new evidence has come to light that at least some of sunlight’s apparent ability to protect against MS is not down to vitamin D at all.
The study in question used an ‘animal model’ of MS known as experimental autoimmune encephalomyelitis (EAE) . In this study, laboratory animals with this condition were exposed to ultraviolet (UV) light. This led to dramatic reductions in the activity of the disease. However, the UV light only brought about a small and transient rise in vitamin D levels in the animals. The magnitude and duration of this rise would be insufficient to account for the considerable benefit conferred by the light.
The authors of this study conclude that “These results suggest that UVR [ultraviolet radiation] is likely suppressing disease independent of vitamin D production, and that vitamin D supplementation alone may not replace the ability of sunlight to reduce MS susceptibility.
Before we get too ahead of ourselves, let us bear in mind that this is an animal model of MS, and only one experiment. However, what it does do is open up the possibility that some, possibly many, of sunlight’s apparent wide spectrum of benefits for the body are not mediated through vitamin D, but by other not-well-understood mechanisms.
1. Raghuwanshi A, et al. Vitamin D and multiple sclerosis. J Cell Biochem 2008;105(2):338-343
2. Becklund B et al. UV radiation suppresses experimental autoimmune encephalomyelitis independent of vitamin D production. Proc Natl Acad Sci 22 Maarch 2010 [epub ahead of print]