Multiple Sclerosis May Start Later for Those Who Spend Teenage Summers in the Sun

A study of people with multiple sclerosis (MS) found that those who spent time in the sun every day during the summer as teens developed the disease later than those reporting not spending time in the sun every day. The study, published in the Oct. 7, 2015 online issue of Neurology^®, the medical journal of the American Academy of Neurology, also found that people who were overweight at age 20 developed the disease earlier than those who were average weight or underweight.

“The factors that lead to developing MS are complex, and we are still working to understand them all, but several studies have shown that vitamin D and sun exposure may have a protective effect on developing the disease,” said study author Julie Hejgaard Laursen, M.D., Ph.D., of Copenhagen University Hospital in Denmark. “This study suggests that sun exposure during the teenage years may even affect the age at onset of the disease.”

Given that MS is the leading cause of non-traumatic disability in young American adults, what does this mean for people’s health and MS risk factors now? Ben Thrower, M.D., medical director of the Andrew C. Carlos Multiple Sclerosis Institute at Shepherd Center in Atlanta advised: “I would not suggest excessive tanning due to the risk of skin cancers later in life. I would suggest that people have vitamin D levels checked periodically starting in childhood. Mega doses of vitamin D without periodic blood testing should also be avoided due to health risks associated with excessive vitamin D.”

For the current study, 1,161 people with MS in Denmark filled out questionnaires and gave blood samples. They were put into two groups based on their sun habits during their teenage years – those who spent time in the sun every day and those who did not spend time in the sun every day. They were also asked about their use of vitamin D supplements during their teenage years and how much fatty fish they ate at age 20.

The people who spent time in the sun every day had an average onset of MS that was 1.9 years later than those who did not spend time in the sun every day. A total of 88 percent of the participants were in the sun every day group. They developed MS at an average age of 32.9, compared to 31 for those who were not in the sun every day.

Those who were overweight at age 20 developed the disease an average of 1.6 years earlier than those who were average weight and 3.1 years earlier than those who were underweight. Eighteen percent of the participants were overweight; they developed the disease at an average age of 31.2.

“The story of what causes MS is complicated with both genetics and the environment playing a role,” Dr. Thrower said. “Studies have shown that low vitamin D levels may be associated with a higher risk of developing MS. Other studies have shown a lower risk of MS relapses and new lesions on MRI when low vitamin D levels are corrected.

“More than 60 genes have been identified that play a role in the risk of developing MS,” he added. “Some of these genes are associated with vitamin D metabolism. So, this current research adds to the already complex story of MS epidemiology.”

Previous studies have shown a relationship between MS risk and obesity in childhood and the teenage years. Obese people are known to have lower blood levels of vitamin D.

“More sunlight and lower body weights in the teen years seem to be associated with a delayed onset of MS in those who are diagnosed with the disease,” Dr. Thrower said. “The correlation between sun exposure and MS likely ties back in with vitamin D levels.”

The current study is limited by the risk of recall bias because study participants were asked to remember their sun, eating and supplement habits from years before, Dr. Laursen noted. Also, only Danish patients were included into the study, so there should be caution when extending the results to different ethnic groups living in different geographic locations, she added.

For more information on MS and the MS Institute at Shepherd Center, visit shepherd.org/ms.