Multiple sclerosis patients who daily spent time in the summer sun as teens developed the disease later than patients who did not so diligently worship the sun, a new study finds. The Copenhagen University researchers also discovered people who were overweight at age 20 developed the disease earlier than those who were average weight or underweight.

Multiple sclerosis (MS) is an unpredictable disease of the central nervous system, a disorder that attacks nerve-insulating myelin, according to the American Academy of Neurology. A patient’s experience of this disease can range anywhere from relatively benign to devastating, as communication becomes disrupted between the brain and other parts of the body. Common symptoms include muscle weakness (in the extremities) and difficulty with coordination and balance.

Other complaints are numbness, pain, speech impediments, tremors, dizziness, and cognitive impairments, such as difficulties with concentration and memory. Worst case scenario for MS includes partial or complete paralysis. The cause is unknown, there is no cure, various treatments are available, though many have profound side effects. Most people experience their first symptoms — usually blurred or double vision, color distortion, or blindness in one eye — between the ages of 20 and 40.

This wide span has intrigued many a researcher. For the current study, Dr. Julie Hejgaard Laursen and her colleagues examined age of onset in a sample population of 1,161 MS patients living in Denmark.


Participants, 325 men and 836 women, gave blood samples for genotyping and also filled out questionnaires. Generally, they provided information about their use of vitamin D supplements while they were teens, along with details about their weight and how much fatty fish they ate at age 20. In particular, the researchers asked patients about their sun habits: Did they spend time in the sun every day while teens?

After collecting and analyzing the data, which included factoring out certain genetic risks to understand independent effects, the researchers discovered two strong associations.

A total of 88 percent of the participants said they’d spent time in the sun every day as teens and, on average, they developed MS at age 32.9. Analyzing the data, the researchers calculated these patients had an average onset that was 1.9 years later than the less sun-worshipping patients, who on average developed symptoms at age 31.

Further analysis indicated 18 percent of the participants had been overweight at age 20. They developed MS at an average age of 31.2, which was 1.6 years earlier than patients of average weight... and a full 3.1 years earlier than underweight participants.

“It appears that both UVB rays from sunlight and vitamin D could be associated with a delayed onset of MS,” Laursen said in a press release, further explaining how obese people are known to have lower blood levels of vitamin D. “However, it's possible that other outdoor factors play a role, and these still have to be identified.”

Source: Laursen JH, Sondergaard HB, Sorensen PS, Sellebjerg F, Oturai AB. Association between age at onset of multiple sclerosis and vitamin D level-related factors. Neurology. 2015.