In a study of people with multiple sclerosis (MS), those who reported spending every day in the sun as teenagers developed the disease an average of 1.9 years later than those who did not spend days in the sun.

Researchers led by Julie Hejgaard Laursen, M.D., Ph.D., Copenhagen University Hospital in Denmark, studied 1,161 people in Denmark who had MS.  Participants filled out questionnaires, were asked about use of vitamin D supplements during teenage years and how much fatty fish they ate at age 20, and gave blood samples. This study was published  in Neurology.

“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,” Laursen said.  “This study suggests that sun exposure during the teenage years may even affect the age at onset of the disease.”

[pullquote]The study found that people of average weight or underweight at age 20 developed the disease later than those who were overweight. [/pullquote]

Of the participants, 88 percent were in the group that was in the sun every day of the summer as teens.  Those who were not exposed to sun daily developed the disease on average at age 31, compared to 32.9 for those with daily sun exposure.

The study also found that people of average weight or underweight at age 20 developed the disease later than those who were overweight.  Of the participants, eighteen percent were overweight and developed the disease 3.1 years earlier than those who were underweight, and 1.6 years earlier than people of average weight. 

This could point to a relationship with vitamin D deficiency and MS, as obese people are known to have lower blood levels of vitamin D, however there is not enough direct evidence to prove a link yet, Laursen said.

“It appears that both UVB rays from sunlight and vitamin D could be associated with a delayed onset of MS,” Laursen said. “However, it’s possible that other factors play a role, and these still have to be identified.”

Limitations of the study include the risk of recall bias, since some people may not accurately recall the amount of sun exposure, and the fact that only Danish patients were included in the study.  The results might not extend to people living in different geographic locations or different ethnic groups.

Funding for the study came from the Danish Multiple Sclerosis Society, Danish Council for Strategic Research and Brodrene Rønje Holding.