Sun Exposure May Protect Against Pediatric-Onset MS

Sun exposure was linked to a lower risk of pediatric-onset multiple sclerosis (MS), a case-control study showed.

Spending 30 minutes to 1 hour outdoors daily during the most recent summer was associated with 52% lower odds of developing pediatric MS compared with spending less than 30 minutes outside per day (adjusted OR 0.48, 95% CI 0.23-0.99, P=0.05), reported Emmanuelle Waubant, MD, PhD, of the University of California San Francisco, and co-authors.

Being outdoors 1 to 2 hours a day dropped the odds by 81% (adjusted OR 0.19, 95% CI 0.09-0.40, P<0.001), they noted in Neurology. Summer ambient ultraviolet ray dose was also protective for MS (adjusted OR 0.76 per kJ/m², 95% CI 0.62-0.94, P=0.01).

The study follows previous work demonstrating links between increased sun exposure in childhood and lower odds of adult-onset MS.

“Sun exposure is known to boost vitamin D levels,” Waubant said in a statement. “It also stimulates immune cells in the skin that have a protective role in diseases such as MS. Vitamin D may also change the biological function of the immune cells and, as such, play a role in protecting against autoimmune diseases.”

Clinical trials are needed to determine whether more sun exposure or vitamin D supplements can prevent MS from developing or alter the disease course, Waubant noted. “Advising regular time in the sun of at least 30 minutes daily especially during summer, using sun protection as needed, especially for first-degree relatives of MS patients, may be a worthwhile intervention to reduce the incidence of MS,” she said.

MS usually strikes adults between the ages of 20 and 50, but about 3% to 10% of MS patients start experiencing symptoms in childhood. Pediatric-onset MS initially is highly inflammatory, and disability landmarks are reached about 10 years earlier than in adult-onset MS.

In their analysis, Waubant and colleagues studied 332 patients ages 3 to 22 who had MS for a median of 7.3 months, comparing them with 534 age- and sex-matched controls without MS.

Questionnaires completed by participants or their parents indicated that 18.7% of young MS patients spent less than 30 minutes daily outdoors during the previous summer, compared with 6.2% of controls.

Overall, links between sun exposure and MS were dose-dependent. Sun exposure in the first year of life also appeared to have a protective relationship with MS, the researchers observed.

Sunscreen use did not appear to change the relationship between sun exposure and MS, Waubant said. Using satellite data, the researchers estimated that children and young adults living in Florida would be 21% less likely than New York residents to develop MS due to exposure to higher summer ambient ultraviolet ray intensity (adjusted OR 0.79, 95% CI 0.67-0.95).

Blood samples showed that higher vitamin D levels, measured as serum 25-hydroxyvitamin D concentrations, were associated with greater odds of MS. However, that analysis was not included in the main results due to possible reverse causality, since routine vitamin D supplementation likely occurred soon after MS was diagnosed.

Recall error is a possible limitation to the study, Waubant and co-authors acknowledged. The study also did not account for physical activity, they added: young people with MS may be more sedentary and less likely to spend time outdoors.