Can Show a Cancer Benefit
In a perplexing finding, a new study
suggests that exposure to sunlight may help people with melanoma
And a second study found sunshine
confers yet another cancer benefit: It may reduce the risk of
developing non-Hodgkins lymphoma.
The results of both pieces of
research raise obvious questions.
"Sunlight is one of only 60 agents
designated by the World Health Organization as an established
human carcinogen," said Kathleen Egan, an associate professor
of medicine at Vanderbilt University School of Medicine and
lead author of an editorial accompanying the studies in the
Feb. 2 issue of the Journal of the National Cancer Institute.
"How is it that this human carcinogen can be associated with
a beneficial impact with regards to cancer?"
The answer is that it might not
be the sunlight per se that is responsible, but some other capacity
of sunlight, specifically its role in vitamin D synthesis, Egan
Scientists have long noted that
while the incidence of melanoma has been rising in developed
nations, so, too, has survival.
To try to understand this apparent
anomaly, the authors of the first study followed 528 individuals
with melanoma for five years. People who scored high on three
measures of sun exposure -- sunburn, high intermittent sun exposure
and solar elastosis (a measure of skin damage due to the sun)
-- and had high skin awareness were less likely to die.
It's not clear what biological
mechanisms are at work, said study author Marianne Berwick,
a professor of internal medicine at the University of New Mexico
Health Sciences Center, but she also pointed to vitamin D as
the logical path of investigation. "We're realizing more and
more that vitamin D controls cell proliferation," she said.
"It's possible that people who
have genetic factors in the vitamin D receptor gene or other
genes in that pathway are less able to metabolize vitamin D
through sunlight or milk, and therefore have a much higher susceptibility
to developing melanoma under low levels of sun exposure," she
Another explanation may be that
sun exposure is linked with less aggressive cancers because
it increases the ability of DNA to repair itself.
Or it may be that there are differences
"There may be a variant of melanoma
that is not linked to sun exposure that tends to be more lethal
than the normal variety," said Dr. Sumayah Jamal, an assistant
professor of dermatology and microbiology at New York University
School of Medicine.
Another expert seemed equally
puzzled by the findings.
"These studies are interesting,
and raise many questions that have to be answered by further
study," said Dr. Martin Weinstock, chairman of the Advisory
Committee on Skin Cancer for the American Cancer Society.
"In the melanoma study, sun exposure
caused more melanomas but there were indications that people
with higher sun exposure had a slightly better prognosis. It
is not clear whether that was the result of sun exposure before
or after the melanoma was diagnosed," He said. "It may be that
the type of melanomas that develop in people who have lots of
sun exposure are not as aggressive as those that arise in people
with less sun exposure."
"Alternately, it might be that
something about sun exposure affects the prognosis of melanoma,"
Weinstock said, "and the researchers suggest vitamin D may act
as a protective factor, but at this point it is too early to
Regardless, the findings should
not be seen as an invitation to bake in the sun. "It's clear
and undeniable that the incidence of melanoma overall is higher
in those with a history of childhood sunburn, of intermittent
sun exposure, and of sun damage," Jamal said.
The second study found that exposure
to ultraviolet (UV) radiation reduced risk for non-Hodgkins
lymphoma. Like melanoma, this type of cancer has also been increasing
The study authors, based in Sweden,
looked at the history of UV exposure and other risk factors
for lymphoma in 3,000 lymphoma patients and a similar number
People with a higher exposure
to UV radiation through sunbathing and sunburns had a decreased
risk of developing non-Hodgkins lymphoma. Specifically, a lot
of sunbathing and sunburns at around the age of 20, and five
to 10 years before the interview for the study, were associated
with a 30 percent to 40 percent reduced risk.
It's too early, however, to determine
if the link is a causal one, the study authors cautioned.
While the link between sunlight
and vitamin D is an established one, the idea of a connection
between vitamin D and cancer is relatively new, Egan said.
And there are other ways to boost
vitamin D. "If people are concerned about their vitamin D production,
the answer is to supplement their diets with vitamin D [fortified
milk] as opposed to going out and getting more sun," Jamal said.