Sun and UVR exposure The researchers’ aim was to “examine the associations of sun exposure (measured as time spent outdoors) and UVR exposure (measured as UVR dose) with risk of pediatric MS.”
The 332 study participants with MS had a median disease duration of 7.3 years and a mean age of 15.9 years; 63.3% were female. They were required to have either MS or clinically isolated syndrome (CIS) onset before age 18 years and be within 4 years of symptom onset.
These participants were compared with 534 age- and sex-matched individuals without MS
(59% female; median age, 15.4 years).
The children with MS did not differ from the control group in race, birth season, or skin color. However, children with MS were more likely to have been exposed to tobacco smoke during their first year of life, and more likely to have ever been overweight.
Participants or their parents/guardians were asked how much time they spent outdoors daily at various ages, and how much time was spent during the previous year.
Serum levels of 25(OH)D and antibodies against Epstein-Barr virus viral capsid antigen (EBV VCA) were higher among the group with MS, compared with the control group.
Risks, benefits During the summer prior to the study, 19% of those with MS reported spending less than 30 minutes outdoors versus 6% of those without the condition.
The researchers found significant correlations between development of MS and the various measures of time spent outdoors, with Pearson correlation coefficients ranging from 0.25 to 0.84 (P < .001) as well as ambient UVR measures (r = 0.76; P < .001).
On the other hand, time outdoors was inversely correlated with ambient UVR dose in the most recent summer (r = –0.15 and –0.17; P < .05).
Levels of antibodies against EBV VCA correlated with age (r = .23; P < .001), whereas being overweight inversely correlated with serum 25(OH)D concentration (r = –0.15; P = .001).
However, serum 25(OH)D concentration correlated with the mother’s education (P < .001), child’s skin color (P < .001), and time spend indoors in the most recent summer (P < .05).
In the fully adjusted model, compared with spending less than 30 minutes outdoors during the most recent summer, greater time spent outdoors was associated with a marked reduction in the odds of developing MS.
The researchers found a dose response, with 30 minutes to 1 hour having a 52% lower odds of MS development. Spending 1-2 hours outside reduced MS odds by 81%.
Spending more than 2 hours in the sun did not provide any additional benefit, the investigators reported.
Higher summer ambient UVR dose “was also protective for MS” (adjusted odds ratio, 0.76 per kJ/m2; 95% confidence interval, 0.62-0.94;
P = .01), the researchers wrote.
Notably, use of sun protection in the most recent summer was not significantly associated with odds of MS development.
Dr. Waubant suggested two possible reasons for these associations: the effect of sun exposure on vitamin D levels and the immunomodulating effect of ultraviolet light through the skin, which has an anti-inflammatory effect.
She noted that providing guidance regarding optimal amounts of sunlight while weighing the risks and benefits is “challenging,” since too much sun exposure without protection also has risks. Dr. Waubant added that spending more than 2 hours outdoors daily did not further reduce the risk for MS, compared with 1-2 hours of outdoors exposure.
Top image credit: Maskot/DigitalVision/Getty Images
Image credit: Maskot/Getty Images