Lifetime Sun Exposure May Reduce Multiple Sclerosis Risk

While many organizations recommend individuals limit their sun exposure due to the risk of skin cancer, those who live in areas in which they are exposed to more UV-B rays may be less likely to develop multiple sclerosis (MS), according to a new study published by Neurology.

The study authors indicate that exposure to UV-B rays during childhood and young adulthood may also reduce the risk of MS.

The link is likely due to the fact that sun exposure helps the body produce vitamin D, of which low levels have been associated with MS development.

Related Coverage: High Dose Vitamin D May Benefit Multiple Sclerosis Patients

“While previous studies have shown that more sun exposure may contribute to a lower risk of MS, our study went further, looking at exposure over a person’s life span,” said study author Helen Tremlett, PhD. “We found that where a person lives and the ages at which they are exposed to the sun’s UV-B rays may play important roles in reducing the risk of MS.”

Included in the study were 151 women with MS and control group of 235 women who were included in the Nurses’ Health Study. Approximately all women were white and had fair to medium skin tone. The participants lived in various climates and locations across the United States.

Participants answered a questionnaire about sun exposure in the summer, winter, and during their lifetime.

The researchers split the patients into cohorts that represented low, moderate, and high UV-B exposure based on latitude, altitude, and average cloud cover for their locations. High summer sun exposure was characterized as more than 10 hours per week and in the winter was characterized as more than 4 hours per week, according to the authors.

In total, 22% of women with MS had high exposure at ages 5 to 15 years, while 41% had low exposure.

The authors discovered that women who lived in sunnier climates who had the highest exposure to UV-B rays had a 45% lower risk of MS compared with those living in areas with the lowest exposure, according to the study.

For specific age groups, participants aged 5 to 15 years who lived in areas with high levels of UV-B rays had a 51% reduced risk of MS compared with the lowest group.

Additionally, participants who spent more time outside between ages 5 to 15 years in high UV-B regions were 55% less likely to develop MS compared with those in the lowest-exposure group, according to the study.

These results suggest that sun exposure may reduce the risk of MS; however, this should be interpreted cautiously since it can cause skin cancer, according to the authors.

“Our findings suggest that a higher exposure to the sun’s UV-B rays, higher summer outdoor exposure and lower risk of MS can occur not just in childhood, but into early adulthood as well. The methods we applied to measure sun exposure could also be used in future studies.” Dr Tremlett said. “In addition, our research showed that those who did develop MS also had reduced sun or outdoor exposure later in life, in both summer and winter which may have health consequences.”