Other experts were similarly cautious in their interpretation of the study’s findings. “This does not change dietary recommendations for fish intake as part of a heart-healthy, anti-inflammatory or broad cancer prevention diet,” Carrie Daniel-MacDougall, an associate professor of epidemiology at the University of Texas MD Anderson Cancer Center, wrote in an email.
Dr. Daniel-MacDougall led an earlier analysis, with a shorter follow-up time and fewer variables, of the same N.I.H.-A.A.R.P. cohort included in the most recent study. Her paper, published in 2011, also found a correlation between fish intake and melanoma risk. However, the N.I.H.-A.A.R.P. study was originally designed to track many types of cancers, and it didn’t measure important and well-known melanoma risk factors, like a history of sunburns or greater lifetime UV exposure, Dr. Daniel-MacDougall wrote. People with these risk factors may have spent more time in the sun — perhaps at the beach or fishing — and may have also been more likely to enjoy seafood, she pointed out. Without more information, it’s impossible to determine if it’s the fish, time in the sun or some other factor driving the greater melanoma risk.
Dr. Sancy Leachman, director of the Melanoma Research Program at Oregon Health & Science University, said the new study was well-designed and called the findings “intriguing.” But, she said, when “you crunch large data sets like this,” what you find are 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 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,” Dr. Leachman said.
Many studies have identified correlations between certain foods and types of cancer, but in general, when more studies are conducted and the results are looked at as a whole, the effects often become smaller or disappear altogether. For melanoma specifically, limited studies have turned up some strange and surprising correlations with certain foods. Eating more citrus fruit has been associated with a greater melanoma risk in some, but not all, studies, for example; and red and processed meat has been associated with lower risk of melanoma but a higher risk of other cancers.
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