New Canadian research has found that those who grow up in sunnier parts of the world may be less likely to develop multiple sclerosis later in life.
Researchers at the University of British Columbia looked at 151 women with MS and 235 women without MS who lived in various locations across the United States and in a variety of climates.
All of the women were a similar age, 98 per cent of the women were white, and 94 per cent reported that they had fair to medium skin. Of those with MS, the average age at onset was 40.
The women were asked to complete questionnaires about their sun exposure in summer, winter and across their lifetime including childhood and adolescence.High sun exposure during summer was defined as more than 10 hours per week, and more than four hours per week in the winter.
The researchers then divided the participants into one of three groups, either low, moderate or high UVB ray exposure based on where they lived.
They found that women who lived in sunnier climates with the highest exposure to the sun's UVB rays had a 45 percent reduced risk of developing MS, compared to those living in areas with the lowest UVB ray exposure.
Although UVB rays can cause sunburn and increase the risk skin cancer, they are also important for helping the body produce vitamin D. Low levels of the vitamin have previously been linked to an increased risk of MS.
When looking at specific age groups, the team found those who lived in areas with the highest levels of UV-B rays during childhood, between ages 5 to 15, had a 51 percent reduced risk of MS later in life compared to the group with the lowest level of exposure to UVB rays.
In addition, those who spent more time outdoors in the summer between the ages 5 to 15, in locations where exposure to UVB rays was the highest, had a 55 percent reduced risk of developing the disease compared to those in the group with the lowest level of exposure.
"While previous studies have shown that more sun exposure may contribute to a lower risk of MS, our study went further, looking at exposure over a person's life span," said study author Helen Tremlett,.
"Our findings suggest that a higher exposure to the sun's UV-B rays, higher summer outdoor exposure and lower risk of MS can occur not just in childhood, but into early adulthood as well."
Tremlett continued, "In addition, our research showed that those who did develop MS also had reduced sun or outdoor exposure later in life, in both summer and winter which may have health consequences."
The findings can be found published online in Neurology, the medical journal of the American Academy of Neurology.