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Tuesday, November 13, 2012

Age and Sun Exposure Related in Risk for MS

 A study in Norway and Italy has found that the patterns of sun exposure is more complicated than earlier research had indicated, in relationship to the risk of multiple sclerosis.

According to Kjetil Bjernevik of the University of Bergen in Norway, Individuals, in both countries, with little sun exposure during childhood and adolescence were at increased risk for developing MS later in life. This is in line with previous studies around the world.

After examination of sun exposure at certain ages during winter versus summer it was learned that the relationship to subsequent MS differed substantially between the two countries, and in ways that did not appear to reflect merely the difference in latitude. Bjernevik announced this in a platform presentation at an annual meeting of the European Committee for Treatment and Research in MS.

He suggested that genetics, sunscreen use, and cultural factors most likely played roles in shaping participants risk for MS.

Bjernevik reported from an analysis of data from an ongoing five-country study called EnvIMS. The data was compiled from completed detailed questionnaires filled out by some 5,700 individuals, including 1,980 with MS, on previous sun exposure, infections, diet, and smoking history.

The current analysis focused on 85% of the participants that are from Norway and Italy.

Because of clothing worn in cold climates and because the amount of ultraviolet radiation reaching the ground is weaker with increasing latitude, previous studies had suggested that MS risk increased in individuals growing up in extreme latitudes where sun exposure is presumably lower than nearer the equator.

Vitamin D is believed to be involved in the mechanism by which sun exposure would influence the risk of MS. Endogenous vitamin D production is driven by sunlight and UV radiation, which in turn appears to correlate with the risk of MS and a number of other diseases.

Participants were asked to rate their sun exposure for different age ranges in the questionnaire from the EnvIMS. The age ranges were – up to 6, 7to 12, 13 to 15, 16 to 18, 19 to 24, and 25 to 30 – separately for summer and winter. For their habits in early childhood participants were encouraged to ask their parents.
Surprisingly, it was learned that during both summer and winter, during early childhood, the Norwegian participants reported substantially more sun exposure than their Italian counterparts.

Before the age of 13 almost none of the Norwegians reported little or no sun exposure either in winter or summer.

On the other hand nearly 40% of the Italians said they received little or no sun exposure in winter when they were 6 or younger, similarly for about 20% between the ages of 7 to 12.

Bjernevik reported that the disparity was smaller in summer between the two countries, but still apparent.

When these age-based patterns of earlier sun exposure in MS patients versus controls were analyzed by Bjernevik and his colleagues, they found the associations differed between the two countries.

The only significant increase in MS risk to the Norwegians came with little summertime sun exposure during the teen years (OR 1.6 to 1.8, P<0.05, after adjusting for gender, compared with participants reporting that they spent substantial time outdoors)

However for the Italians the significant (P<0.05) risks were associated with little sun exposure in summer at age 6 and younger and at ages 25 to 30 (OR 1.5 to 1.6), and in winter only at ages 7 to 12 (OR 1.5).

In Norway, age-specific sun exposure in winter was not a factor in subsequent MS risk.

Bjernevik explained that in earlier research it was indicated that when sunscreens were applied, as recommended, they blocked enough UV radiation to essentially abolish endogenous vitamin D production. So the questionnaires ask about past sunscreen use during the same age ranges.

Bjernevik reported that a “high” use of sunscreen in childhood prior to age 13, but not after, was significantly associated with increased MS risk at odds ratios of 1.4 to 1.5 (P<0.05) after adjusting for age, sun exposure, and physical activity. Self-reported high use at ages 25 to 30, in fact, was associated with a 20% decrease in risk that just missed statistical significance.

Corresponding data was not reported for Italy.

George Ebers, MD. Of the University of Oxford in England, session co-moderator, commented that the findings of this study, as well as others linking decreased sun and UV exposure to MS risk, have implications for public health.

He noted that because of skin cancer risks many countries have instituted policies to discourage sun exposure, especially in children and teens.

Yet this relationship, too, is more complicated than is usually portrayed” Ebers said. He cited research showing that people with outdoor jobs, such as utility workers, have a lower incidence of skin cancers than the general population.

He suggested that other health risks that may stem from insufficient sun exposure have been neglected due to the zeal to prevent skin cancer.

Policies of many countries....may have unexpected biological effects” Ebers said.

The study was funded by the Western Norway Regional Health Authority and multiple sclerosis associations in Italy, Norway, and Canada.

Study authors and Ebers reported no relevant financial interests. 
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Primary source: European Committee for Treatment and Research in Multiple Sclerosis
Source reference: Bjørnevik K, et al "An age at exposure effect in the association between sun exposure and the risk of MS in Norway and Italy. The EnvIMS study" ECTRIMS 2012.

Source: MedPage Today © 2012 MedPage Today, LLC. (11/10/12)

Original story: Sun exposure, age related in MS risk
Source: Multiple Sclerosis Resource Centre