, research shows. The use of sunscreen does not appear to affect the risk.
“This is the first study, as far as we are aware, to investigate the effect of sun exposure in pediatric MS,” first author Prince Sebastian, of the ANU Medical School, Australian National University, Canberra, said during a presentation at the meeting held by the Americas Committee for Treatment and Research in Multiple Sclerosis.
“In order to reduce the incidence of MS, parents should be encouraged to allow their children to spend at least 30 minutes outdoors in the sun every day, while using adequate sun protection,” Mr. Sebastian said.
“This is especially important for children with a family history of MS,” he said. As the findings show, “you can use adequate sun protection and still get the benefit of sun exposure in terms of MS risk reduction.”
Low sun exposure, exposure to ultraviolet light, and vitamin D have been well established as modifiable risk factors for MS in adults. However, research is lacking on the effect of these factors upon patients younger than 18 years who have pediatric MS, a less common form of the disease. Pediatric MS constitutes about 5% of all MS cases.
To investigate the issue, Mr. Sebastian and colleagues evaluated data on 332 patients with pediatric MS who were between the ages of 4 and 22 years. The patients were enrolled at 16 MS centers around the United States. They were compared by sex and age with 534 control persons aged 3-22 years who did not have MS.
For the patients with MS, the median disease duration was 7.3 months, and 63% were female. The median age of the patients was 15.9 years.
Compared with those who did not have MS, patients with MS were significantly less likely to have been exposed to cigarette smoke (17.8% vs. 14.2%). They were significantly more likely to be overweight (23.8% vs. 14.2%), and the median anti-VCA level was higher (3.7 vs. 2.2).
Those who were exposed to the sun during the most recent summer for a duration of 30 minutes to 1 hour daily, as determined on the basis of self-report or parent report, had a 2.6-fold reduced risk of having MS, compared with those who spent less than 30 minutes outdoors daily (odds ratio, 0.39; P < .05), after adjusting for age, sex, birth season, the child’s skin color, the mother’s education, smoke exposure, being overweight, and Epstein-Barr virus infection.
Sun exposure for 1-2 hours daily was associated with a 7.4-fold reduced risk for MS, compared with exposure of 30 minutes or less (OR, 0.13; P < .001).
The odds were similar for those with 2-3 hours of sun exposure (OR, 0.21; P < .001) and for those with more than 3 hours of daily exposure (OR, 0.14; P < .001), versus less than 30 minutes.
Mr. Sebastian and his team also assessed the role of summer ambient levels of UV light and whether such exposure conferred a similar degree of protection. The risk for MS was lower among those who were exposed to higher summer ambient UV levels than among those exposed to lower levels (OR, 0.80; P = .046).
He noted, “Based on the results, individuals residing in Florida (28° N) would have 20% lower odds of MS, compared with an individual residing in New York (40° N).”
Interestingly, median rates of the use of sun protection were similar for the participants with MS and those without MS (OR, 0.95), suggesting that the use of sunscreen did not reduce the protective effect of sun exposure.
“We predicted that greater use of protection would limit effective sun exposure and would therefore increase MS risk,” Mr. Sebastian said, “but we don’t see that, and it’s probably because someone who uses sun protection likely gets more sun exposure anyway.”
“Our results suggest that you can use adequate sun protection and still get most of the benefit in terms of MS prevention, which is quite encouraging,” he added.
For those with MS, median serum 25(OH)D levels were higher (27.7 ng/mL vs. 23.7 ng/mL; P < .001), but Mr. Sebastian noted that this difference was likely attributable to the use of vitamin D supplementation after an MS diagnosis. An important limitation of the study was a lack of data on supplementation.