By Pat Anson, Editor

Exposure to sunlight may elevate your risk of sunburn, skin cancer and other health problems, but it appears to have a beneficial effect in delaying the onset of multiple sclerosis (MS).

Danish researchers found that MS patients who spent time in the sun every day during the summer as teenagers developed the disease later in life than those who spent their summers indoors. Their study, which was published in the online issue of Neurology, also found that people who were overweight at age 20 developed MS earlier.

"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, MD, 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."

MS is a chronic and incurable disease which attacks the body’s central nervous system, causing numbness in the limbs, difficulty walking, paralysis, loss of vision, fatigue and pain.

Ultraviolet rays (UVB) in sunlight are a principal source of Vitamin D, which has a wide range of positive health effects, such as strengthening bones and inhibiting the growth of some cancers.

In the Danish study, over 1,100 people with MS 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. 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 nearly two years later than those who did not spend time in the sun. On average, they developed MS at age 33, compared to 31 for those who were not in the sun every day.

"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 outdoor factors play a role, and these still have to be identified."

Those who were overweight at age 20 developed MS about 1.6 years earlier than those of average weight and 3.1 years earlier than those who were underweight.

Previous studies have shown a relationship between MS and childhood obesity. Obese people are also known to have lower blood levels of vitamin D.

"The relationship between weight and MS might be explained by a vitamin D deficiency, but there's not enough direct evidence to establish this yet," Laursen said.

"A limitation of the study is the risk of recall bias because participants were asked to remember their sun, eating and supplement habits from years before," Laursen said. "In particular, someone with a long history of MS and onset of the disease at an early age, may wrongly recall a poor sun exposure. Additionally, 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."