Data from 29,000 adults showed those with the highest mercury levels in their blood were 79% more likely to report having had a non-melanoma skin cancer than those with the lowest levels.
“People are generally exposed to mercury by consuming fish contaminated with methylmercury,” said study coauthor Eunyoung Cho of the Warren Alpert Medical School of Brown University in Providence, Rhode Island.
“Scientists haven’t really thought about mercury causing skin cancer,” Cho said by email.
The current study doesn’t prove that mercury does cause skin cancer, but the research team hopes the findings will stimulate more research, Cho said.
Methylmercury is a form of the pollutant that was commonly released from factories into waterways before environmental regulations in many parts of the world cracked down on the practice due to health concerns.
Mercury levels vary in different types of seafood, leading regulators to advise against eating lots of swordfish, for example, but not to limit salmon.
Pregnant women are advised to eat much less seafood due to potential developmental risks to babies posed by mercury exposure.
Skin cancer, however, isn’t among the many risks of mercury-contaminated fish that are widely recognized, the study team notes in the British Journal of Dermatology.
Researchers analyzed data from annual health surveys of nationally-representative samples of adults between 2003 and 2016 that included blood tests. In the current study, survey participants were 49 years old, on average, and 468 of them, or about 1.6%, reported ever having had a non-melanoma skin cancer.
Risks were higher for non-Hispanic white participants, but were similar for men and women.
One limitation of the study is that researchers lacked data from medical records to verify skin cancer diagnoses. They also lacked data on many other skin cancer risks, including hair color and skin pigmentation, number of moles and any history of indoor tanning or severe sunburns.
“Although this study reveals an association between excess mercury exposure and non-melanoma skin cancer, causation is not well understood,” said Dr. Aaron Farberg of the Icahn School of Medicine at Mount Sinai in New York City.
While people should be aware of the potential skin cancer risk associated with mercury in fish, it’s not the main cause of these malignancies and the exact skin cancer risk associated with mercury exposure isn’t yet clear, Farberg, who wasn’t involved in the study, said by email.
“It is well established that exposure to solar UV is the greatest risk factor for skin cancer,” Farberg said.