A new study reports that sunlight or UV light from lab sources reduces autoimmune damage to myelin nerve sheaths. Phototherapy is already an established treatment for immune disorders of the skin, including psoriasis and dermatitis. But the light does not penetrate deep enough to affect myelin sheaths directly. So what's happening?
Researchers have observed that multiple sclerosis (MS) is more common at high latitudes than in the tropics. The prevalence as a function of latitude is reported in the April 24 issue of Science News:
1. Nigeria, about 5 to 10 degrees north latitude: five MS cases per 100,000 population,
2. Tunisia, about 35 to 40 degrees north latitude: ten MS cases per 100,000 population,
3. Sweden, about 55 to 70 degrees north latitude: 100 MS cases per 100,000 population.
Similar results from other countries show that sunny areas have lower rates of MS. One possible reason for this is the difference in vitamin D production caused by exposure to UV light. But vitamin D deficiency has never been linked to MS.
There is an animal model of MS produced by injecting mice with proteins that instigate damage to myelin sheaths. Researchers at the University of Wisconsin studied the effects of UV light and vitamin D on this animal model. They found that UV light was effective at suppressing the disease even when the exposure was low enough to have negligible effect on vitamin D production.
Thus, the UV light must be doing something else. At this point it is not known what other molecules important for MS may be formed or changed by the light, or why MS appears to be more susceptible than other autoimmune diseases. However, the authors of the paper in Proceedings of the National Academy of Sciences report, “vitamin D supplementation alone may not replace the ability of sunlight to reduce MS susceptibility”.
The National Multiple Sclerosis Society reports 400,000 cases of MS in the United States, with an average of 200 more diagnosed each week. Their website offers updates on current research.