Half an hour of daily sun exposure can cut MS risk


Children, adolescents, and young adults who spend 30 minutes outside in the sun daily may cut their risk of developing multiple sclerosis (MS) in half, new research suggests.

Investigators compared more than 300 children, teens, and young adults with MS aged 3-22 years with more than 500 matched participants without MS.

After adjusting for MS risk factors, participants who spent an average of 30 minutes to 1 hour outside daily during the previous summer had a 52% lower chance of developing MS, compared with those who spent less than 30 minutes outdoors daily. Additionally, those who spent 1-2 hours outdoors daily had an 81% lower risk for MS.

“We found that spending between 1 and 2 hours outdoors daily provided the most benefit but spending as little as 30 minutes outside daily may cut the risk of MS roughly in half,” coinvestigator Emmanuelle Waubant, MD, PhD, professor of neurology, Weill Institute for Neurosciences, at the University of California, San Francisco, said in a press release.

“The take-home message is that spending more time outdoors in the sun can be helpful to prevent [an] autoimmune disease like MS,” she said.

The findings were published online Dec. 8, 2021, in Neurology.

Dr. Emmanuelle Waubant
We found that spending between 1 and 2 hours outdoors daily provided the most benefit but spending as little as 30 minutes outside daily may cut the risk of MS roughly in half.

‘Meaningful’ research

Although MS onset typically occurs between the ages of 20 and 50 years, 3%-5% of individuals with MS begin experiencing symptoms before they reach 18 years, the researchers noted.

MS etiology is “understood to be a combination of genetic predisposition, infectious exposures, and other environmental and behavioral risk factors,” they wrote.

Particularly, low sun exposure, low ultraviolet radiation (UVR) exposure, and low vitamin D status are environmental risk factors for adult-onset MS, with increased risk associated with “insufficient sun exposure in childhood.”

Previous research has primarily focused primarily on adult populations, Dr. Waubant said.

Studying genetic and environmental aspects of MS in children in the current study was “very meaningful” because the investigators were able to get closer to time of exposure than in adult MS studies, allowing them to have more detailed information, she added.

The researchers analyzed data from a multicenter case-control study investigating environmental risk factors for pediatric MS.

Sun and UVR exposure

The researchers’ aim was to “examine the associations of sun exposure (measured as time spent outdoors) and UVR exposure (measured as UVR dose) with risk of pediatric MS.”

The 332 study participants with MS had a median disease duration of 7.3 years and a mean age of 15.9 years; 63.3% were female. They were required to have either MS or clinically isolated syndrome (CIS) onset before age 18 years and be within 4 years of symptom onset.

These participants were compared with 534 age- and sex-matched individuals without MS
(59% female; median age, 15.4 years).

The children with MS did not differ from the control group in race, birth season, or skin color. However, children with MS were more likely to have been exposed to tobacco smoke during their first year of life, and more likely to have ever been overweight.

Participants or their parents/guardians were asked how much time they spent outdoors daily at various ages, and how much time was spent during the previous year.

Serum levels of 25(OH)D and antibodies against Epstein-Barr virus viral capsid antigen (EBV VCA) were higher among the group with MS, compared with the control group.

Risks, benefits

During the summer prior to the study, 19% of those with MS reported spending less than 30 minutes outdoors versus 6% of those without the condition.

The researchers found significant correlations between development of MS and the various measures of time spent outdoors, with Pearson correlation coefficients ranging from 0.25 to 0.84 (P < .001) as well as ambient UVR measures (r = 0.76; P < .001).

On the other hand, time outdoors was inversely correlated with ambient UVR dose in the most recent summer (r = –0.15 and –0.17; P < .05).

Levels of antibodies against EBV VCA correlated with age (r = .23; P < .001), whereas being overweight inversely correlated with serum 25(OH)D concentration (r = –0.15; P = .001).

However, serum 25(OH)D concentration correlated with the mother’s education (P < .001), child’s skin color (P < .001), and time spend indoors in the most recent summer (P < .05).

In the fully adjusted model, compared with spending less than 30 minutes outdoors during the most recent summer, greater time spent outdoors was associated with a marked reduction in the odds of developing MS.

The researchers found a dose response, with 30 minutes to 1 hour having a 52% lower odds of MS development. Spending 1-2 hours outside reduced MS odds by 81%.

Spending more than 2 hours in the sun did not provide any additional benefit, the investigators reported.

Higher summer ambient UVR dose “was also protective for MS” (adjusted odds ratio, 0.76 per kJ/m2; 95% confidence interval, 0.62-0.94;
P = .01), the researchers wrote.

Notably, use of sun protection in the most recent summer was not significantly associated with odds of MS development.

Dr. Waubant suggested two possible reasons for these associations: the effect of sun exposure on vitamin D levels and the immunomodulating effect of ultraviolet light through the skin, which has an anti-inflammatory effect.

She noted that providing guidance regarding optimal amounts of sunlight while weighing the risks and benefits is “challenging,” since too much sun exposure without protection also has risks. Dr. Waubant added that spending more than 2 hours outdoors daily did not further reduce the risk for MS, compared with 1-2 hours of outdoors exposure.

Top image credit: Maskot/DigitalVision/Getty Images
Image credit: Maskot/Getty Images

A causal relationship?

Commenting on the study, Helen Tremlett, PhD, professor and Canada research chair in Neuroepidemiology and Multiple Sclerosis at the University of British Columbia, Vancouver, said she was “impressed with the investigators’ rigorous methods,” which were detailed and careful.

They also “thought through the implications,” said Dr. Tremlett, who was not involved with the research.

She noted that, if there “really is a causal relationship here, it does suggest that practicing safe sun exposure could reduce the risk of MS.”

Dr. Tremlett added that the investigators “acknowledge that practicing safe sun exposure can be challenging, but [they] walk the audience carefully through that – advising regular time in the sun, at least 30 minutes per day in summer.”

The researchers also noted the importance of using sun protection as needed, “which could be particularly advisable for people at high risk for developing MS; for example, those with a first-degree family member with MS,” Dr. Tremlett said.

The study was funded by the National Institutes of Health and the National MS Society.
Dr. Waubant reported having received personal fees outside the submitted work from MS@TheLimit, MS curriculum, PRIME, DBV, Emerald, Jazz Pharma, and The Corpus.
Dr. Tremlett has collaborated with several study authors on other research but not on this particular study. She disclosed no relevant financial relationships.