More outdoor time and sun exposure reduced the likelihood of developing multiple sclerosis (MS) in children and young adults, a case-control study found.
Children and young adults who spent an average of 30 minutes to an hour outside daily during the most recent summer had a 52% lower chance of MS compared with those who spent an average of less than 30 minutes outdoors daily (adjusted OR 0.48, 95% CI 0.23-0.99, P=0.05), reported Emmanuelle Waubant, PhD, of the University of California San Francisco, and co-authors.
Those who averaged 1-2 hours outside daily had 81% lower odds of MS than those who spent an average of less than 30 minutes (adjusted OR 0.19, 95% CI 0.09-0.40, P<0.001).
Higher ambient ultraviolet radiation (UVR) exposure also reduced the odds of being in the MS group (adjusted OR 0.76 per kJ/m2, 95% CI 0.62-0.94, P=0.01), the researchers wrote in Neurology.
Overall, the findings were consistent with earlier data about relationships between adult-onset MS and low sun exposure.
“Providing guidance on the best amounts of sunlight exposure to get while weighing the benefits against the risks is challenging,” Waubant said in a statement. “We found that spending between one and two hours outdoors daily provided the most benefit, but spending as little as 30 minutes outside daily may cut risk of MS roughly in half.”
“It’s important to note that too much sun exposure without protection also has risks, and our study found that spending two hours or more outside daily did not further reduce the risk of MS compared to one to two hours,” she added.
Waubant and colleagues studied 332 patients from 16 pediatric MS centers in the U.S. ages 4 to 22 who had MS or clinically isolated syndrome diagnosed before age 18, and 534 age- and sex-matched controls. Median disease duration for MS patients was 7.3 months.
Participants or their parents answered questionnaires about residence, medical history, and environmental exposures. Participants also provided a blood sample for serum vitamin D, measured as 25(OH)D, and serum IgG for Epstein-Barr virus (EBV) viral capsid antigen (VCA).
“As serum 25(OH)D levels were post-diagnostic, limiting any conclusions about their association with MS risk, we did not include 25(OH)D in the main analyses,” the authors noted.
Sun exposure was assessed with estimates of time spent outdoors daily during weekends and holidays. Use of sun protection (hats, sunglasses, clothing, and sunscreen) was estimated on a 4-point scale ranging from never to always, while average daily ambient UVR dose by residence location was available from monitoring instruments for the period of 2000 to 2018.
Children with MS spent less time outdoors during summer and were less likely to use sun protection than controls but were exposed to similar ambient UVR doses. Serum levels of 25(OH)D and antibodies against EBV VCA were higher among children with MS compared to controls.
Although use of sun protection was not associated with odds of having MS, the authors noted that “including all three sun-related predictors in the same model improved model fit compared to models including any one of them alone (P<0.01).”
Other findings included:
- Greater time outdoors during the first year of life was also associated with reduced MS risk, though with lower effect size than that for the most recent summer.
- Higher levels of antibodies against EBV VCA conferred greater odds of MS (adjusted OR=1.45 per unit, 95% CI 1.30-1.62; P<0.001).
- Higher serum 25(OH)D concentration was associated with greater odds of MS (adjusted OR=1.07 per ng/mL, 95% CI 1.05-1.09; P<0.001) in a model including sun protection, ambient summer UVR dose, and serum 25(OH)D concentration, with no interactions with time outdoors, use of sun protection, and ambient UVR levels.
Post-hoc analysis restricted to children with MS onset <4 months prior to enrollment also found higher serum 25(OH)D levels still associated with greater odds of MS, though not statistically significant. Post-hoc analysis restricted to children diagnosed <2 months prior to enrollment found higher serum 25(OH)D concentration were associated with lower odds of MS, “although the effect was not statistically significant, likely due to the reduced sample size,” the authors noted.
About 3% to 10% of MS patients experience symptoms before age 18, with longer progression to irreversible disability though occurring at an earlier patient age compared with adult-onset MS.
“To our knowledge, this is the first study to investigate the effect of sun exposure in pediatric MS, a form of the disease that occurs on average 20-30 years earlier than in adults,” Waubant and colleagues wrote.
“Clarifying the causal effect of modifiable risk factors, such as sun exposure and vitamin D status, could reduce the disease burden associated with MS,” they noted. “Our findings suggest that advising regular time in the sun of at least 30 minutes daily 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 pediatric MS.”
Limitations of the study include possible recall error in data about sun exposure and use of sun protection, since questionnaires were completed retrospectively.
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Spending 30 minutes outside daily cut risk of pediatric-onset MS roughly in half, a case-control study showed. Spending between 1 to 2 hours outdoors daily provided the most benefit.
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Findings were consistent with the large body of work on relationships between low sun/ultraviolet radiation exposure and adult-onset MS.
Paul Smyth, MD, Contributing Writer, BreakingMED™
The study was supported by the National Institutes of Health and the National MS Society.
Waubant reported personal fees from MS@TheLimit, MS curriculum, PRIME, DBV, Emerald, Jazz Pharma, and The Corpus.
Cat ID: 36
Topic ID: 82,36,730,36,138,192,925
