Exposure to sunlight may reduce the risk of advanced breast
cancer in women with light skin pigmentation, according to the
results of a population-based study appearing in the American
Journal of Epidemiology.
"We believe that sunlight helps reduce women's risk of breast
cancer because the body manufactures the active form of vitamin D
from exposure to sunlight," lead author Dr. Esther M John, from the
Northern California Cancer Center in Fremont, said in a
statement.
"It is possible that these effects were observed only among
light-skinned women because sun exposure produces less vitamin D
among women with naturally darker pigmentation."
The study is not the first to link sun exposure with a reduced risk
of breast cancer, but the way that sun exposure was measured was
new, according to John.
"We measured women's skin pigmentation on the forehead (usually
exposed to the sun) and on the upper inner arm (usually not exposed
to the sun) and used the difference between the two measurements as
a measure of past sun exposure. Other studies have usually relied
on self-reported sun exposure," she said.
The study included 1788 women with breast cancer and a comparison
group of 2129 controls - women without breast cancer, living the
San Francisco Bay Area of California (1995-2003).
In addition to the sun exposure test mentioned, skin specimens
were obtained and analyzed in a subgroup of subjects in each
group.
High levels of sun exposure were associated with a 47% reduced risk
of advanced breast cancer in light-skinned women, the results
show.
Mutations of the vitamin D receptor gene did not affect the
association.
However, this association was not seen in women with medium or dark
skin and was only apparent for advanced disease, not localized
breast cancer.
The results could have important public health implications, but
they will require confirmation in other studies, the authors
conclude.
"While the public needs to be advised to avoid excessive sun
exposure and sun burns in particular because of the known risk of
skin cancer and melanoma, never getting any sun exposure leads to
vitamin D deficiency," John said.
The evidence is increasing that vitamin D may decrease the risk of
certain cancers, such as breast, prostate and colon cancers.
A safe way to get vitamin D is from supplements.
