February 7, 2011 — A new study appears to cement the suspected link between sun exposure and lower rates of multiple sclerosis (MS).
The Australian case-control study found that past and current sun exposure and serum vitamin D levels are independently associated with a reduced risk for a central nervous system (CNS) firstdemyelinating event (FDE). The association remained after adjusting for potential confounders and did not vary by study region, sex, or type of demyelination.
The study is unique in several ways, said one of the study authors, Anne-Louise Ponsonby, PhD, professor at the Murdoch Children's Research Institute in Melbourne, Australia. For example, it included more than 1 site, enrolled people with ademyelinating event who had not yet been diagnosed as having MS, and investigated both sun and vitamin D levels simultaneously.
"The study raises the question of whether sun exposure itself is important, separate from vitamin D," said Dr. Ponsonby. She acknowledged that although the sun is believed to have direct immune effects in addition to providing vitamin D, the sun exposure effect found in thestudy could simply reflect longer-term vitamin D status. "In any case, it's important to study both vitamin D and sun exposure to understand the effects on immune function and MS."
The Autoimmune Study is published in the February 8 issue of Neurology.
The study included 282 patients from 4 regions of Australia with varying latitudes (Brisbane City, Newcastle, Geelong City andWestern Districts of Victoria, and the island of Tansmania) who had a first clinical diagnosis of CNS demyelination within the study period. Of these, 16 had a distinct event during the study period, whereas others may have had a previous event. The study also included 542 controls randomly selected from the Australian Electoral Roll, 395 of whom were matched to an eligible FDE case.
Inclusion ofsubjects with an FDE rather than established MS minimized changes in behavior, said Dr. Ponsonby. "It means it was before they introduced any disease-related changes to their lifestyle." About 60% of people presenting with a demyelinating event will progress to MS within 10 years, she said.
The multisite nature of the study allowed the researchers to compare various latitudes. "We designed thestudy so we could not only look at sun exposure and vitamin D but also see how much of that was accounted for by latitude gradient," said Dr. Ponsonby.
Through questionnaires, researchers collected information on sun exposure during leisure time (weekends and holidays) in summer and winter for different periods of life (6-10 years, 11-15 years, 16-20 years, and last 3 years). With this information,the researchers were able to examine past sun exposure before the onset of MS.
Determining sun exposure before the age of 6 years would have been too problematic, said Dr. Ponsonby. "At least by the age of 6 or 10 years, people have anchoring events like going to primary school, so they might have some recall of their sun exposure."
Researchers also gathered data on subjects' propensity to tanor burn, their number of freckles as a teenager, smoking history, educational level, physical activity, diet, and use of vitamin D supplements. As well, they noted each patient's eye and skin color and grades of actinic skin damage and collected blood samples for DNA and vitamin D analysis.
Accumulated Sun Exposure
The study showed that both sun exposure and current vitamin D levels contributedindependently to reduced FDE risk. Accumulated leisure time sun exposure, defined as the dose per 1000 kJ/m2 at the age of 6 years to present, had an adjusted odds ratio (AOR) of 0.70 (95% confidence interval [CI], 0.53 – 0.94) for each UV dose increment of 1000 kJ/m2.
For vitamin D, the AOR for decreased FDE risk was 0.93 (95% CI, 0.86 – 1.00) per 10-nmol/L increase in serum 25-hydroxyvitamin...