August 8, 2003
Australian researchers report new evidence that increased sun exposure during ages 6 to 15 is associated with a decreased risk of multiple sclerosis, an autoimmune disease of unknown cause. Dr. I. A. F. van der Mei and colleagues (University of Tasmania, Hobart, Australia) report their efforts in the August 9 issue of the British Medical Journal (2003;327:316).
MS occurs with much greater frequency in temperate zones farther from the equator, than in tropical zones, closer to the equator. One possible explanation for this is that an environmental factor associated with latitude (distance from the equator) may contribute to the development of MS, or protect against it. MS is less common in tropical areas, which are exposed to greater ultraviolet radiation (UVR, a form of radiation that has shorter wavelengths than visible light and therefore carries more energy) than temperate zones. Recent research indicates that UVR (or vitamin D which is synthesized in the body as a result of UVR exposure) can dampen the immune attack. This might provide a biological explanation for reduced frequency of MS where UVR exposure is higher.
Dr. van der Mei’s team examined 136 people with MS and 272 controls without MS who were residents of the island of Tasmania, the part of Australia most distant from the equator. Participants were asked about the amount of time they spent in the sun in the winter and summer, as well as measures used to protect against the sun and use of vitamin D supplements at ages 10 to 15 years. The approximate age of sun exposure also was determined. The investigators obtained silicone casts of the hand, which measure “actinic damage” – damage from chemically active sun rays.
The results show that higher sun exposure during ages 6 to 15 was associated with a lower risk of MS. Greater actinic damage was also associated with a decreased risk of MS.
Although this was a relatively small study in a limited geographic area, it formed the basis for a new research grant awarded by the National MS Society to Anthony J. McMichael, MBBS, PhD (The Australian National University, Canberra). Dr. McMichael’s study will examine the association between UVR exposure and both MS and “first demyelinating event” (a single, isolated neurologic event suggesting demyelination, loss of nerve-fiber insulation). In addition, his study will not be confined to Tasmania, a temperate zone, but will extend throughout the tropical areas of Australia where UVR exposure is likely to be higher.
Colleen Hayes, PhD (University of Wisconsin-Madison) is investigating possible mechanisms for a link between sun exposure and MS. She has evidence that vitamin D can lead to the production of beneficial immune chemicals, or cytokines, in mice with an MS-like disease, and reverse or prevent its occurrence. With funding from a Society research grant, she is examining how vitamin D thus may stop the immune attack in MS.
These studies may provide new insights into factors that make people
susceptible to the development of MS, and may suggest new avenues for treatment
Copyright © 2003, The National Multiple Sclerosis Society