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Prenatal and early life sun exposure was associated with lower risk for relapse in children with pediatric-onset multiple sclerosis (MS), a new prospective cohort study showed.

At least 30 minutes of daily summer sun in the first year of life was associated with a lower risk for relapse in children who later developed MS than less exposure, investigators found. The same was true with daily prenatal exposure of at least 30 minutes during the second trimester.

“These novel findings suggest that sun exposure in early development may have long-lasting benefits on subsequent MS course, possibly through modulation of the immune response,” lead author Gina Chang, MD, MPH, of the Children’s Hospital of Philadelphia, Philadelphia, and colleagues wrote.

The findings were published online on February 12 in Neurology.

Exploring Sun Exposure and Risk

While symptoms of adult MS typically strike between ages 20 and 50 years, 3%-5% of individuals with MS experience symptoms before age 18 years.

Identifying potential risk factors for relapse is important in individuals with pediatric MS, who have higher relapse rates and reach irreversible disability a median 10 years earlier than those with adult-onset MS, investigators noted. 

A lack of sunlight, low exposure to ultraviolet radiation (UVR), and low levels of vitamin D have been associated with increased MS risk in adults and children, past studies have shown. However, the link between sun exposure and MS remains poorly understood, especially in children.

The new study included 334 patients at 18 pediatric MS clinics around the United States. Participants were between ages 4 and 21 years at baseline, and recruitment took place from 2011 to 2017.

Participants had onset of MS or clinically isolated syndrome before reaching age 18 years and were 4 years from symptom onset.

Information on demographics, medical history, and behaviors related to sun exposure (eg, use of sunscreen or clothing to block the sun) prenatally and during childhood was collected from participants or their legal guardian.

Data on participants was entered prospectively from the time of their first clinic visit, which could have taken place at the time of or before study enrollment, and subsequent clinic visits, which occurred one to two times per year, on average.

Investigators captured information on participants’ use of disease-modifying treatment (DMT) and data on disease relapse, defined as new or recurrent symptoms lasting for at least 24 hours after a 30-day remission without fever or infection. 

From children with MS, the researchers gathered detailed information on time spent in the sun during infancy and during weekends and holidays in the summer preceding study enrollment. Biological mothers provided information on sun exposure during pregnancy. Information on ambient UVR dose during these time periods was also collected.

Benefit of Sun Exposure?

By the end of study follow-up (median, 3.3 years), 62% of participants had relapsed at least once.

Relapses were less common among children who spent 30 minutes to an hour in the sun every day during the summer of their first year of life than those with less sun exposure (45% vs 65%).

After adjusting for type of MS medication taken, season of birth, tobacco exposure in the first year of life, and sun protection used, investigators found that childhood sun exposure before age 1 year was associated with a 33% lower risk for relapse than less time in the sun (adjusted hazard ratio [aHR], 0.67; P = .01). 

In a seemingly contradictory finding, investigators found that children born in the summer had a 37% higher risk for symptom relapse (aHR, 1.63; P = .02) than those born in winter. 

“We hypothesize that this may be partly due to patients born in the summer having less overall sun exposure in their first year of life because they may have been intentionally sheltered from direct sunlight because of being a newborn,” investigators wrote.

Although not statistically significant, investigators did find that use of mid-efficacy DMT and treatment with high-efficacy DMT were associated with increased relapse risk vs no DMT use (both P = .08). This may be due to reverse-causality, as high- and mid-efficacy treatments are often reserved for patients with a more aggressive disease form of MS, researchers wrote.

When examining prenatal sun exposure, researchers found that ≥ 30 minutes of daily sun exposure during the second trimester and greater prenatal UVR dose in the 6 months before birth were associated with lower relapse risk in offspring with pediatric MS (aHR, 0.68; P = .04 and HR, 0.69; P = .03, respectively). 

“Future studies should look at how time in the sun at other time periods before and after MS diagnosis affects disease course to better guide sun exposure recommendations for children with MS and to help design potential clinical trials,” Chang said in a press release.

One study limitation involved possible recall error from questionnaires on sun exposure and use of sun protection. It is also possible that participants changed sun-exposure–related behaviors after enrollment in the study, the report stated.

The study was funded by the National Multiple Sclerosis Society, Biogen, EMD Serono, and Novartis. Chang reported no relevant financial relationships.