Infrequent outdoor activity and sunscreen use are risk factors for multiple sclerosis, according to a new study.
Multiple sclerosis (MS) is an autoimmune disease where the body’s own immune system attacks nerves in the brain and spinal cord. Researchers believe vitamin D plays a role in MS through its ability to smarten and help control the immune system. Research to date suggests that getting good amounts of sun exposure throughout life (which leads to better vitamin D levels) may prevent MS. We’ve covered MS in great detail on our site, and more information can be found here.
Researchers in the present study wanted to hone in on the relationship between sun exposure and MS in the countries of Italy and Norway.
They used data from the International multicenter case-control study of Environmental Factors in Multiple Sclerosis (EnvIMS study). This was a large study which sent questionnaires to populations across countries in both Europe and North America collecting data on potential risk factors of MS.
The researchers were interested in the countries of Norway and Italy because Norway receives little sunlight and sits at a northerly latitude, while Italy is a Mediterranean country that sits closer to the equator and gets more sunlight compared to Norway. Despite Italy’s proximity to the equator, they still have a high prevalence of MS, with 116 MS cases per 100,000 persons (as of 2013). Norway has a prevalence of 160 cases per 100,000 persons (as of 2013).
The researchers looked at 953 cases of people with MS and 1,717 controls in Norway and 707 cases of people with MS and 1,333 controls in Italy. They asked them questions based on amount of outdoor activity, amount of sun exposure during vacation, the use of sunscreen, and other factors relating to sun exposure such as skin color and hair color.
They wanted to know if people with MS in Italy had different personal sun exposure histories verse Norway and vice-versa. They also wanted to know if the healthy controls had different personal sun exposure histories verse those with MS.
And indeed, the researchers found differences.
In general, they found that infrequent outdoor activity led to an increased risk of MS in both countries. For Norway, infrequent outdoor activity between the ages of 13 and 18 years most increased risk of MS, while in Italy, infrequent outdoor activity between the ages of birth and 5 years most increased risk of MS.
When the researchers looked at sunscreen use, they found that frequent use of sunscreen between the ages of birth to 12 years in Norway led to an increased risk of MS. They found no relationship in Italy at any age interval.
“In this large case-control study, both frequency of outdoor activity and sunscreen use early in life were associated with subsequent MS risk,” the researchers concluded. “Thus, converging evidence from different measures suggest that low sun exposure in early life increases MS risk.”
Since this was a case-control study asking participants to remember information from their childhood, there is always the risk of what is called recall bias. Recall bias is a limitation where participants may not remember their answers accurately. Additionally, the researchers noted that the small sample size could be a limitation.
The researchers call for further studies to better understand relationship between sun exposure, vitamin D and MS.