Sun Exposure in Teen Years May Delay Onset of MS
But researchers only found a connection, not cause-and-effect link
The precise cause of MS is unknown, but research suggests it arises from a combination of genetic vulnerability and certain environmental triggers. Inadequate vitamin D -- a nutrient needed for normal immune function -- is considered one of the suspects.
The new findings support the theory that "avoiding sunlight" could be one of the triggers for MS, said study lead researcher Dr. Julie Laursen, of the Danish Multiple Sclerosis Center, in Copenhagen, Denmark.
Since sun exposure is closely connected to people's vitamin D levels, it's possible that the vitamin explains the later MS onset, Laursen said. However, she stressed, the findings do not "directly" support that.
The researchers found no relationship between MS onset and patients' reported use of multivitamins or vitamin D as teenagers.
According to Laursen, it's possible that sunlight, like vitamin D, has its own beneficial effects on the immune system.
In the study, adults with multiple sclerosis were asked about their "summer sun" habits and supplement use during their teens. They were also asked to recall their weight at age 20.
It turned out that MS arose later -- at the average age of 33 -- among people who'd gotten some sun every day as teenagers. Among people who'd gotten less sun, MS developed at age 31, on average.
People's weight at age 20 also seemed to matter: Those who'd been overweight developed MS almost two years earlier, on average, than those who'd been at normal weight at 20.
Body fat, Laursen explained, also happens to be related to vitamin D: People who are overweight tend to have lower blood levels of the vitamin.
Again, though, it's not clear that vitamin D explains the connection between weight and multiple sclerosis, Laursen said.
The study does, however, support the theory that adolescence is a critical time in MS development, according to Laursen. She said more research is needed to see whether there are roles for sun exposure, body weight, vitamin D, or all three.
LaRocca agreed. "It's a complex picture," he said.
In the meantime, LaRocca said, people can talk to their doctors about whether a vitamin D supplement is a good idea. They can also get the vitamin through certain foods, he added -- including fatty fish, and cereals and dairy products fortified with vitamin D.
The study findings were published online Oct. 7 in the journal Neurology.