Study sheds light on link between sun exposure and multiple sclerosis

A new study suggests that children, teens and young adults who spend more time outdoors during the summer months and live in areas of the country that expose them to greater amounts of ultraviolet light have a lower risk of developing multiple sclerosis as children. While rare, multiple sclerosis can develop in children, although most people start to get symptoms of the disease between the ages of 20 and 50. The research is published in the December 8, 2021, online issue of Neurology®, the medical journal of the American Academy of Neurology. The study also found that those who had more sun exposure during their first year of life also had lower odds of multiple sclerosis.

“Providing guidance on the best amounts of sunlight exposure to get while weighing the benefits against the risks is challenging,” said study author Emmanuelle Waubant MD PhD, of the University of California San Francisco and a Fellow of the American Academy of Neurology. “We found that spending between one and two hours outdoors daily provided the most benefit, but spending as little as 30 minutes outside daily may cut risk of multiple sclerosis roughly in half.”

The study involved 332 people with multiple sclerosis who had the disease for an average of seven months. They were matched with 534 people of similar age and sex who did not have multiple sclerosis. Participants ranged in age from 3 to 22 years.

Sun exposure was measured as time spent outdoors, use of sun protection like a hat, clothing and sunscreen, plus the amount of ultraviolet light exposure based on where participants lived at birth and at the time of the study. The children or their parents or guardians answered a questionnaire about how much time they spent outdoors daily at various ages and in the past year.

In the summer before the study, 19% of the participants with multiple sclerosis said they spent less than 30 minutes outdoors, compared to 6% of those who did not have multiple sclerosis. And 18% of the participants with multiple sclerosis spent one to two hours outdoors, compared to 25% of those without multiple sclerosis.

After adjusting for smoke exposure, sex and other factors that could affect multiple sclerosis risk, researchers found that people who spent an average of 30 minutes to an hour outside daily in the summer before the study had a 52% lower chance of multiple sclerosis compared to those who spent an average of less than 30 minutes outdoors daily. Those who averaged even more time outside daily, between one and two hours, had an 81% lower chance of multiple sclerosis than those who spent an average of less than 30 minutes outdoors daily.

“It’s important to note that too much sun exposure without protection also has risks, and our study found that spending two hours or more outside daily did not further reduce the risk of multiple sclerosis compared to one to two hours,” Waubant said.

Greater time spent outdoors in the first year of life was associated with lower odds of multiple sclerosis. Researchers found location also mattered. More intense sunlight where a participant lives was associated with lower odds of multiple sclerosis. For example, researchers estimate that someone living in Florida is 21% less likely to have multiple sclerosis compared to someone living in New York.

The study does not prove that sun exposure prevents multiple sclerosis, but it shows an association.

A limitation of the study is that children and their parents or guardians had to recall sun exposure and use of sun protection from years earlier and that recall may not be accurate.

The study was supported by the National Institutes of Health and the National Multiple Sclerosis Society.

Source: News Release
American Academy of Neurology
December 8, 2021