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Spending more time in the summer sun and living in generally sunnier places appears to provide protection against pediatric-onset multiple sclerosis (MS), an international team of scientists reported.
Spending at least 30 minutes outdoors in sunlight each day is associated with a significantly reduced risk of childhood MS, the team said.
Prince Sebastian, a third-year medical student at the Australian National University in Canberra, presented the team’s findings at the virtual Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) Forum 2021, in a talk titled “Low Sun Exposure is a Risk Factor for Pediatric-Onset Multiple Sclerosis.”
MS typically appears between the ages of 20 and 50, “but around 5% of cases actually begin before the age of 18,” Sebastian said.
A lack of sunlight and low vitamin D levels are known risk factors for adult-onset MS, but their role in pediatric-onset MS is less clear. One theory poses that pediatric MS is due to a child’s heavier load of modifiable risk factors, such as limited sunlight exposure.
“If that is true,” Sebastian said, “then that could imply a greater potential for intervention in terms of prevention and treatment.”
Sebastian and colleagues recruited 332 children with pediatric-onset MS and 534 age- and sex-matched healthy children (control group) from across 16 pediatric MS centers in the U.S. to study whether sunlight, ultraviolet radiation (UVR), and vitamin D levels influence disease onset.
Researchers analyzed associations between time spent outdoors in the summer (sun exposure), the use of sun protection, ambient UVR levels based on participant’s location over their lifetime, vitamin D status (assessed by blood levels of 25-hydroxyvitamin-D), and the risk of MS.
Factors taken into consideration included a child’s sex, age, race, birth season, skin color, mother’s education, cigarette smoke exposure in the first year of life, weight (especially being overweight), and Epstein-Barr virus infection.
Results showed that spending time outdoors did, in fact, correlate with a lower risk of pediatric MS.
“Even spending 30 minutes to one hour produced a relatively large and statistically significant reduction in risk, compared to the reference category of less than 30 minutes,” Sebastian said.
Compared with children who spent less than 30 minutes outside, those spending up to an hour outdoors each day during the most recent summer had a 2.6 times lower MS risk. Spending one to two hours outside translated to 7.4 times lesser risk.
Higher ambient summertime UVR levels also appeared to offer some MS protection. A child living in Florida (a latitude of 28° north of the equator) would have a 20% reduction in MS risk compared to one living in New York (40° north), Sebastian said as an example. (Ultraviolet radiation exposure is known to be greater in latitudes closer to the equator than those more distant from it.)
An expected result — but one not seen in this study — concerned the use of sun protection. Researchers thought that heavier use of sun lotion would link with a greater childhood MS risk, since such protection is effectively another way to limit sun exposure.
“That’s probably because people who tend to use sun protection also tend to get more sun exposure anyway,” Sebastian said of this result. “Whereas if someone doesn’t use sun protection at all, it’s quite likely they’re just staying indoors all the time.”
Median vitamin D levels were higher in MS patients (27.7 nanograms/mL) than in controls (23.7 nanograms/mL). This surprising finding suggested, Sebastian said, that “children with MS might have been taking vitamin D supplementation following their diagnosis.”
Overall, the team concluded that “spending more time in the sun during summer — even 30 minutes daily — is associated with greatly reduced MS [risk] in children,” Sebastian said.
“Living in a sunnier location with higher summer UVR levels” also helps to lower the “risk for MS in children,” he added.
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