Can your diet really affect your risk of skin cancer?

NEW YORK – A large study published this month found a surprising link between fish consumption and the development of melanoma, the most serious type of skin cancer. But although the finding raises questions about possible links between diet and melanoma, the study’s lead author and other experts cautioned that this is no reason to avoid eating fish. It also doesn’t change the most important tip for reducing the risk of melanoma: Limit your exposure to UV rays from the sun or tanning booths.

The new study, published in the journal Cancer Causes & Control, assessed data from more than 490,000 adults in the United States aged 50 to 71 who were enrolled in the National Institutes Diet and Health Study. of Health-AARP. At the start of the study, participants completed detailed questionnaires, including information about their fish consumption, and then were followed for about 15 years to track cancer diagnoses within the group. Compared to those who ate virtually no fish, the group that ate the most — an average of 10 ounces, or about three servings, per week — had 22% more cases of malignant melanoma, the researchers found.

It’s unclear why eating fish might affect the risk of developing melanoma, said Dr. Eunyoung Cho, associate professor of dermatology at Brown University and lead author of the study. “We think it’s not fish per se, but probably a contaminant in the fish,” she said. Other studies have shown that people who eat more fish have higher levels of heavy metals such as mercury and arsenic in the body. These same contaminants are also associated with a higher risk of skin cancer, she noted. However, her study did not measure contaminant levels in participants, and more research is needed to explore this link, she said.

“I wouldn’t discourage people from having fish just because of our discovery,” Dr Cho said. Fish consumption is associated with a lower risk of cardiovascular disease and possibly even certain other cancers, she said. The American Cancer Society recommends choosing fish, poultry, and beans more often than red meat, and the American Heart Association (AHA) advises eating two servings of fish per week for heart health. (One serving is 3 ounces of cooked fish, according to the AHA, or about three-quarters of a cup of flaked fish.)

Other experts have been equally cautious in their interpretation of the study results. “This does not change dietary recommendations for eating fish as part of a heart-healthy, anti-inflammatory or broad cancer prevention diet,” wrote Dr. Carrie Daniel-MacDougall, associate professor of epidemiology. at the University of Texas MD Anderson Cancer Center. in an email.

Dr. Daniel-MacDougall conducted an earlier analysis, with shorter follow-up time and fewer variables, of the same NIH-AARP cohort included in the most recent study. His paper, published in 2011, also found a correlation between fish consumption and melanoma risk. However, the NIH-AARP study was originally designed to follow many types of cancers, and it did not measure important and well-known melanoma risk factors, such as a history of sunburn or greater lifetime UV exposure, wrote Dr. Daniel-MacDougall. People with these risk factors may have spent more time in the sun — perhaps at the beach or fishing — and may also have been more likely to enjoy seafood, he said. she declared. Without more information, it is impossible to determine if it is the fish, the time spent in the sun, or another factor that increases the risk of melanoma.

Dr Sancy Leachman, director of the melanoma research program at Oregon Health & Science University, said the new study was well designed and called the results “intriguing”. But, she said, when “you deal with large data sets like this,” you find correlations between factors, not evidence that one causes another. This type of study is good for developing new hypotheses — that contaminants found in fish might increase the risk of melanoma, for example — but they need a lot more research to see if they hold up.

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

Many studies have identified correlations between certain foods and certain types of cancer, but in general, when more studies are conducted and the results are looked at as a whole, the effects often diminish or completely disappear. For melanoma in particular, limited studies have found strange and surprising correlations with certain foods. Eating more citrus fruits has been associated with a greater risk of melanoma in some studies, but not all, for example; and red and processed meat has been associated with 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 get overwhelmed by this incomplete data that has yet to be proven,” Dr. Leachman said. “Stick to the things that work: eat well, sleep well, exercise well, all in moderation,” she said. “It gives you the most resilience possible against any type of disease, including cancer.”

And for melanoma in particular, “the most effective practices we have for preventing melanoma are limiting sun exposure – lifelong, starting in childhood – and screening for skin cancer,” said writes Dr. Daniel-MacDougall.

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

Check your skin regularly for spots that seem new, changing, or unusual, and see a doctor if you find anything concerning, Dr. Leachman said. “If you see something that looks funny, don’t blow it up,” she said. “The sooner you can get it checked out, the better off you’ll be.”

This article originally appeared in The New York Times.

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