Sun Exposure Linked to Reduced Pediatric MS Risk

Nancy A. Melville

March 05, 2021

Children who have higher levels of sun exposure appear to have a substantially lower risk of developing pediatric multiple sclerosis (MS) than children who are less exposed to the sun, new 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, Australia, said during a presentation of the research at the Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) 2021.

"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," Sebastian told Medscape Medical News.

"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 (UV) 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, Sebastian and his 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 to 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 [OR], 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 to 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 to 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), vs less than 30 minutes.

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 a 20% lower odds of MS compared to 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," 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," Sebastian 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 Sebastian noted that this difference was likely due to the use of vitamin D supplementation after an MS diagnosis. An important limitation of the study was a lack of data on supplementation.

Stronger Effect of Frequent Sun Protection

Previous studies have shown a link between sun exposure and MS. A study published in 2018 compared 2251 patients with MS with 4028 control persons who did not have MS. The participants were in Canada, Italy, and Norway.

In that study, for most of the patients with MS, the age of onset was >18 years. In that study, there was a nearly 50% increased risk among those with the lowest degree of summer sun exposure in comparison with those who had the highest level of exposure (risk ratio [RR], 1.47).

Contrary to the current study, that study did show an effect of the use of sun protection ― those with the lowest degree of sun exposure during summer and winter and the highest use of sun protection had the highest risk for MS. They had a 76% increased risk compared with those who had the highest degree of sun exposure and the least use of sun protection (RR, 1.76).

Sandra Magalhaes, PhD, of the University of New Brunswick, Fredericton, Canada, who was first author on that study, noted that the new study of pediatric MS adds valuable evidence on the issue.

"This study is important, as it adds to the etiological literature on MS implicating relevance of sun exposure," Magalhaes told Medscape Medical News.

"We have a number of studies that have demonstrated an important effect of reduced levels of sun exposure and increased risk of MS. However, these studies focus on adult-onset MS populations; rather, the new study adds to the existing literature, as it also implicates sun exposure in etiology of pediatric-onset MS," she said.

Notably, their previous work, unlike the current study, showed that among those who experienced low levels of sun exposure, the risk for MS was higher for those who used sunscreen frequently.

"Overall, in their limited time outdoors, use of sunscreen may further increase risk of MS, which makes sense, since limited time outdoors in less sun, adding sun protection means [exposure to] even less sun."

The findings of both studies support the bulk of research indicating that sun exposure is beneficial with regard to MS.

"There is a need for promoting balanced safe sun practices to reduce disease burden, especially in countries and cultures where children spend a lot of time indoors," Magalhaes said. "Sun exposure has a number of important physiological roles, including vitamin D synthesis but also immune system functioning."

Sebastian and Magalhaes have disclosed no relevant financial relationships.

Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) 2021: Abstract S1.3. Presented February 25, 2021.

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