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: msrc.co.uk Multiple Sclerosis Resource Centre |
