Background and objectives

This study aims to determine the contributions of sun exposure and ultraviolet radiation (UVR) exposure to risk of pediatric-onset multiple sclerosis (MS).

Methods

Children with MS and controls recruited from multiple centers in the United States were matched on sex and age. Multivariable conditional logistic regression was used to investigate the association of time spent outdoors daily in summer, use of sun protection, and ambient summer UVR dose in the year before birth and the year before diagnosis with MS risk, with adjustment for sex, age, race, birth season, child's skin color, mother's education, tobacco smoke exposure, being overweight, and Epstein-Barr virus infection.

Results

Three hundred thirty-two children with MS (median disease duration 7.3 months) and 534 controls were included after matching on sex and age. In a fully adjusted model, compared to spending <30 minutes outdoors daily during the most recent summer, greater time spent outdoors was associated with a marked reduction in the odds of developing MS, with evidence of dose-response (30 minutes-1 hour: adjusted odds ratio [AOR] 0.48, 95% confidence interval [CI] 0.23-0.99, p = 0.05; 1-2 hours: AOR 0.19, 95% CI 0.09-0.40, p < 0.001). Higher summer ambient UVR dose was also protective for MS (AOR 0.76 per 1 kJ/m², 95% CI 0.62-0.94, p = 0.01).

Discussion

If this is a causal association, spending more time in the sun during summer may be strongly protective against developing pediatric MS, as well as residing in a sunnier location.

The objective of this study was to determine whether family members of patients with pediatric multiple sclerosis (MS) have an increased prevalence of autoimmune conditions compared with controls. Data collected during a pediatric MS case-control study of risk factors included information about various autoimmune diseases in family members. The frequency of these disorders was compared between cases and controls. There was an increased rate of autoimmune diseases among family members of pediatric MS cases compared with controls with first-degree history of MS excluded (OR = 2.27, 95% CI 1.71-3.01, p < 0.001). There was an increased rate of MS among second-degree relatives of pediatric MS cases compared with controls (OR = 3.47, 95% CI 1.36-8.86, p = 0.009). The OR for MS was 2.64 when restricted to maternal relatives and 6.37 when restricted to paternal relatives. The increased rates of autoimmune disorders, including thyroid disorders and MS among families of patients with pediatric MS, suggest shared genetic factors among families with children diagnosed with pediatric MS.