A new study warns consuming higher amounts of tuna and non-fried fish appears to be associated with a greater likelihood of malignant melanoma and state 0 melanoma, according to a recent report published in the journal Cancer Causes and Control.
“This study is important because it’s very large and it’s prospective by design, meaning that fish intake was assessed before the development of cancer,” said author Eunyoung Cho, an associate professor of dermatology and epidemiology at Brown University.
“Although fish intake has increased in the US and Europe in recent decades, the results of previous studies investigating associations between fish intake and melanoma risk have been inconsistent — our findings have identified an association that requires further investigation.”
The Brown University researchers found a median daily fish intake of 42.8 grams (1.5 ounces) compared to a median daily fish intake of 3.2 grams (.11 ounces) had a 22% higher risk of malignant melanoma and a 28% increased risk of developing stage 0 cancer, otherwise known as melanoma in situ, where abnormal cells are only in the outer layer of the skin, the study’s release noted.
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The American Cancer Society says melanoma is the fifth most common cancer in the US, with a lifetime risk of 2.6% for White people, 0.1% for Black people and 0.6% for Hispanic people.
“A serving size of cooked fish is approximately 140-170 grams (5-6 ounces); a can of tuna is 142 grams (5 ounces),” the release said.
The study recruited 491,367 adults from across the US to the National Cancer Institute’s NIH-AARP Diet and Health Study between 1995 and 1996, with an average age of 62 among the participants.
The study analyzed the portion size and how frequently the participants ate three types of fish: 1) fried fish, 2) non-fried fish and 3) tuna during the previous year.
Using cancer registries, the researchers tracked the incidence of new melanomas over a median period of 15 years, while accounting for other factors that could influence the result, such as sociodemographic factors, smoking history, family history of cancer, daily intake of alcohol, daily intake of caffeine and calories, and the average ultraviolet radiation levels in each participant’s local area, per the release.
5,034 participants (1%) developed malignant melanoma while 3,284 (0.7%) developed stage 0 melanoma, per the release.
Although the study didn’t show significant associations between eating fried fish and the risk of malignant melanoma or stage 0 melanoma, the researchers found higher intake of non-fried fish and tuna was associated with an increased risk of malignant melanoma and stage 0 melanoma.
But the authors note the study has some limitations, including the analyzes did not account for certain risk factors for melanoma, including mole count, hair color or history of sun-related behaviors.
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Another limitation was the study may not have had a complete representation of the participants’ lifetime diet because their average daily fish intake was calculated only at the beginning of the study.
And because it’s an observational study, it could not conclude a causal link between fish intake and melanoma risk.
“We speculate that our findings could possibly be attributed to contaminants in fish, such as polychlorinated biphenyls, dioxins, arsenic and mercury,” Cho said.
“Previous research has found that higher fish intake is associated with higher levels of these contaminants within the body and has identified associations between these contaminants and a higher risk of skin cancer. However, we note that our study did not investigate the concentrations of these contaminants in participants’ bodies and so further research is needed to confirm this relationship.”
The researchers don’t recommend any changes to fish consumption, but suggest more research is needed to determine if certain components of fish, particularly the contaminants like mercury, are contributing to the association between fish consumption and melanoma risk.