Photo: Sunrise 
Sunlight might be helpful when
treating MS; © Uli Carthäuser /

Vitamin D may reduce the symptoms of multiple sclerosis (MS), researchers argue. But a new study suggests that the ultraviolet portion of sunlight may play a bigger role than vitamin D in controlling MS.

Multiple sclerosis (MS) is much more common in higher latitudes than in the tropics. Because sunlight is more abundant near the equator, researchers have wondered if the high levels of vitamin D engendered by sunlight could explain this unusual pattern of prevalence.

The ultraviolet (UV) portion of sunlight stimulates the body to produce vitamin D, and both vitamin D and UV can regulate the immune system and perhaps slow MS. The new study was designed to distinguish the role of vitamin D and UV light in explaining the high rate of MS away from the equator, says study author Hector DeLuca.

"Since the 1970s, a lot of people have believed that sunlight worked through vitamin D to reduce MS," says DeLuca. "It's true that large doses of the active form of vitamin D can block the disease in the animal model. That causes an unacceptably high level of calcium in the blood, but we know that people at the equator don't have this high blood calcium, even though they have a low incidence of MS. So it seems that something other than vitamin D could explain this geographic relationship."

Using mice that are genetically susceptible to MS-like disease, the researchers triggered the disease by injecting a protein from nerve fibers. The researchers then exposed the mice to moderate levels of UV radiation for a week. After they initiated disease by injecting the protein, they irradiated the mice every second or third day.

The UV exposure (equivalent to two hours of direct summer sun) did not change how many mice got the MS-like disease, but it did reduce the symptoms of MS, especially in the animals that were treated with UV every other day, DeLuca says.

DeLuca stresses that the study, may or may not lead to a new mode of treatment. "There are several ways this could go. If we can find out what the UV is producing, maybe we could give that as a medicine. In the short term, if we can define a specific wavelength of light that is active, and it does not overlap with the wavelengths that cause cancer, we could expose patients who have been diagnosed with MS to that wavelength."; Source: University of Wisconsin-Madison