Living in sunnier climes when young might help shield you from multiple sclerosis decades later, new research suggests.
The main factor may be the sun's ultraviolet B (UV-B) rays, which help the body produce vitamin D, according to a Canadian team. They noted that lower levels of vitamin D have been associated with a rise in risk for multiple sclerosis (MS).
The finding isn't entirely new -- other studies have shown lower MS rates in sunnier regions. But, "our study went further, looking at exposure over a person's life span," explained lead study author Helen Tremlett, of the University of British Columbia in Vancouver.
Tremlett's team tracked the histories of 151 women with MS who were diagnosed at an average age of 40, and 235 women of similar age without MS. The women lived across the United States and nearly all were white.
Women who lived in sunnier regions and had the highest exposure to UV-B rays were 45 percent less likely to develop MS than those who lived in regions with the lowest UV-B exposure, the study found.
Sun exposure in youth was key: Women who lived in regions with the highest levels of UV-B exposure between the ages of 5 and 15 were 51 percent less likely to develop MS than those with the lowest UV-B exposure between ages 5 and 15, Tremlett's group found.
More time spent outdoors in summer in youth was similarly tied to lower MS rates decades later, the researchers reported March 7 in Neurology.
"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," Tremlett said in a journal news release.
Still, exposure to the sun's UV rays has a big down side, too: skin cancer. The American Cancer Society has long warned that tanning and burning, especially, are a prime cause of potentially deadly forms of the disease, such as melanoma.
Regarding the MS study, one expert said its findings are in tune with prior research.
"While geographic location during adolescence was previously known to be associated with MS risk, the current study demonstrates that sun exposure even later in life affects MS risk," said Dr. Asaff Harel, a neurologist at Lenox Hill Hospital in New York City.
Harel noted, however, that almost all of the study group was white, so, "it will be interesting to determine whether the same relationship applies in a more multi-ethnic study."
The U.S. National Institute of Neurological Disorders and Stroke has more on multiple sclerosis.
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