Study suggests sun exposure during first year of life may reduce MS relapses

Getting at least 30 minutes of daily summer sun in the first year of life may mean a lower relapse risk for children who are diagnosed with multiple sclerosis (MS) later, according to a study published on February 12, 2025, online in Neurology® Neuroimmunology & Neuroinflammation, an official journal of the American Academy of Neurology. The study also found if a child's biological mother had at least 30 minutes of daily sun during the second trimester of pregnancy, the child had a lower risk of MS relapses. The study does not prove that sun lowers relapse risk for children with MS, it only shows an association.

"It is important not to spend too much time in the sun without sun protection, however greater exposure to sun has been tied in previous research to a lower risk of developing MS in childhood," said Gina Chang, MD, MPH, of The Children's Hospital of Philadelphia and member of the American Academy of Neurology.

It's encouraging that our study found that greater sun exposure during early development may also be beneficial in helping to reduce disease activity in children who are later diagnosed with MS."

Gina Chang, The Children's Hospital of Philadelphia

For the study, researchers looked at health records from 18 MS clinics across the United States to identify 334 children and young people with childhood-onset MS age four to 21. Participants were within four years of experiencing their first symptoms. The median follow-up time was 3.3 years.

To determine sun exposure, participants' parents or guardians completed questionnaires that asked how much time the participant and their biological mother had spent in the sun at various periods of life, what kind of clothing they typically wore and how often they used sunscreen.

Of the total group, 206, or 62%, experienced at least one relapse during the study. Relapses were defined as new or returning symptoms lasting for at least 24 hours and separated by at least 30 days from the last MS attack, without a fever or infection.

They found that of 75 participants who had 30 minutes to an hour of daily summer sun during their first year of life, 34 children, or 45%, had a relapse. Of the 182 participants who had less than 30 minutes of daily summer sun during their first year of life, 118 children, or 65%, had a relapse.

After adjusting for factors such as tobacco exposure in the first year of life, season of birth, the type of MS medication taken and use of sun protection such as sunscreen, hats and clothing, researchers found that 30 or more minutes of daily summer sun during the first year of life was associated with a 33% lower risk of relapse compared to less than 30 minutes of daily summer sun.

Researchers also looked at sun exposure for the biological mothers of the children.

They found that 30 minutes or more of daily sun during the second trimester of pregnancy was associated with a 32% reduced risk of relapse for their child with MS.

"Our findings suggest that sun exposure in early childhood may have long-lasting benefits on the progression of childhood-onset MS," said Chang. "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."

A limitation of the study was that it relied on participants' parents or guardians reporting their sun exposure and use of sun protection, which they may not have remembered accurately.

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