Individuals' Risk of Melanoma Increases with Time Outdoors, Especially in High-Sunlight Areas

woman sitting outside( — Researchers have shown for the first time that
individual risk of melanoma, the most serious form of skin cancer, is associated
with the intensity of sunlight that a person receives over a lifetime. Published
in the journal Cancer Research*, the study also indicates that the risk of
melanoma for non-Hispanic whites increases with increased time outdoors – even
for men and women who can develop a deep tan.

Scientists have long recognized that rates of melanoma are higher in areas
that are closer to the equator or receive more sunlight, and that ultraviolet-B
rays are the primary cause of sunburn and skin cancer. In this study, the
authors developed a novel approach to measure an individual’s sun exposure over
a lifetime, taking into account where an individual has lived throughout his or
her life. This information determines average annual UVB intensity – the average
amount of ultraviolet-B rays that a person could be exposed to per year over his
or her lifetime. The data led the researchers to conclude that a 10 percent
increase in the average annual intensity was associated with a 19 percent
increase in the individual’s risk for melanoma in men and a 16 percent increase
in women, at any age.

“We’re learning more about the kinds of exposures that cause melanoma,” said
Thomas Fears, Ph.D., the first author of the paper and a scientist at the
National Cancer Institute in Bethesda, Md. “The risk of melanoma is greatest for
people who develop little or no tan. However, we’ve learned that where people
live as both kids and adults and how much UVB shines in those places are
important factors – regardless of tanning ability.”

According to Fears, it is not unusual to see at least a 10 percent difference
in intensity between two locations. New Orleans, for example, receives 20
percent more UVB each year than Atlanta.

In addition to estimating individual risk, the authors analyzed the number of
hours that study participants spent outdoors. They found that the number of
summer hours spent outside prior to age 20 was much larger than after age 20. In
light of this distinction, the researchers hypothesized that differences in
melanoma risk previously attributed to the “critical period” of childhood may,
in fact, be due to the larger number of hours that children typically spend
outdoors compared to adults.