Study links increased risk of skin cancer to fish consumption

A large study published June 8 found a surprising link between eating fish and developing melanoma, the most serious type of skin cancer.

The finding raises questions about possible links between diet and melanoma, but the study’s lead author and other experts cautioned that this should not be a reason to avoid fish. The results also don’t change the most important advice for reducing melanoma risk: limiting exposure to ultraviolet (UV) rays from the sun or tanning beds.

The new study, published in the journal Cancer Causes & Control, evaluated data from more than 490,000 adults in the United States between the ages of 50 and 71 who were enrolled in the NIH-AARP Diet and Health Study. American Association of Retired Persons).

At the start of the study, participants filled out detailed questionnaires, including information on fish intake. They were followed for approximately 15 years to screen for cancer diagnoses among the group. Compared with people who ate almost no fish, the group that ate the most — an average of 287 grams, or about three servings, a week — had 22% more cases of malignant melanoma, the researchers found.

It’s unclear why eating fish can affect a person’s risk of developing melanoma, said Eunyoung Cho, an associate professor of dermatology at Brown University and the study’s lead author. “We believe it’s not the fish itself, but probably some contaminant that’s in the fish,” she said.

Other studies have found that people who eat more fish have higher levels of heavy metals, such as mercury and arsenic, in their bodies. These same contamination factors are associated with an increased risk of skin cancer, Cho noted. However, her study did not measure levels of contamination in participants, and more research is needed to explore this link, she said.

“I wouldn’t discourage people from eating fish just because of our discovery,” Cho said. Eating fish is associated with a lower risk of cardiovascular disease and perhaps even other cancers, she pointed out.​

The American Cancer Society recommends eating fish, poultry, and beans more often than red meat, and the AHA (American Heart Association) advises eating two servings of fish a week for heart health. (One serving equals 86 grams of cooked fish, according to the AHA, or about three-quarters of a cup of flaked fish.)

Other experts were similarly cautious in interpreting the study’s findings. “It does not alter dietary recommendations for eating fish as part of a heart-healthy, anti-inflammatory, or general cancer prevention diet,” Carrie Daniel-MacDougall, associate professor of epidemiology at the MD Cancer Center, wrote in an email in an email. Anderson at the University of Texas.

Dr. Daniel-MacDougall led an earlier analysis, with a shorter follow-up period and fewer variables, of the same NIH-AARP group included in the most recent study.

Her work, published in 2011, also found a correlation between fish intake and melanoma risk. However, the NIH-AARP study was originally designed to screen for multiple types of cancer, and did not measure important and known risk factors for melanoma, such as a history of sunburn or increased lifetime UV exposure, Daniel wrote. -MacDougall.

People with these risk factors may have spent more time in the sun — perhaps at the beach or fishing — and may also be more likely to consume seafood, she pointed out. Without more information, it’s impossible to determine whether it’s fish, time in the sun, or some other factor that increases your risk of melanoma.

Sancy Leachman, director of the Melanoma Research Program at the Oregon Health and Science University, said the new study was well designed and called the findings “intriguing.” But when “processing large datasets like this,” she said, what you find are correlations between factors, not evidence that one causes the other.

These types of studies are good for developing new hypotheses — that contaminants found in fish can increase the risk of melanoma, for example — but they need much more research to see if they hold up.

“Science evolves, and you can’t do everything overnight. That’s just part of the process,” said Dr. Leachman.

Many studies have identified correlations between certain foods and types of cancer, but in general, when more studies are carried out and the results are viewed as a whole, the effects become smaller or disappear altogether.

For melanoma in particular, limited studies have revealed some strange and surprising correlations with certain foods. Eating more citrus fruits has been linked to a higher risk of melanoma in some but not all studies, for example. And red and processed meat have been linked to a lower risk of melanoma, but a higher risk of other cancers.

When it comes to correlations between cancer risk and specific foods, “don’t be scared off by incomplete data that still needs to be proven,” Leachman said. “Stick to the tried and true things: eat well, sleep well, exercise, all in moderation,” she said. “This gives you the greatest resilience you can have against any type of disease, including cancer.”

And for melanoma specifically, “the most effective prevention practices we have are limiting sun exposure – throughout life, starting in childhood – and screening for skin cancer,” wrote Dr. Daniel-MacDougall.

Compared with the limited data on fish and other dietary factors, there is much more evidence to support this advice, agreed Dr. Leachman. Having five or more sunburns in a lifetime doubles your risk of melanoma, and using a tanning bed can increase your risk by 75%, according to the Skin Cancer Foundation.

Check your skin regularly for any blemishes that appear to be new, changing or unusual, and see a doctor if you find anything concerning, Leachman said. “If you see something that looks different, don’t throw it away,” she said. “The sooner you are examined, the better.”

Translated by Luiz Roberto M. Gonçalves