PROVIDENCE, R.I. — Fish tends to have a reputation for being one of the healthier foods you can eat, but a new study finds too much can actually increase your risk of developing skin cancer. Researchers from Brown University discovered that consuming more fish significantly raises a person’s chances for malignant melanoma — the deadliest form of skin cancer.
Concerningly, the team found fried fish wasn’t the biggest culprit here. In fact, eating more tuna and non-fried fish contributed to higher cancer odds.
“Melanoma is the fifth most common cancer in the USA and the risk of developing melanoma over a lifetime is one in 38 for white people, one in 1,000 for Black people and one in 167 for Hispanic people. Although fish intake has increased in the USA 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,” says corresponding author Eunyoung Cho in a media release.
Less than one fish a day increases cancer risk
Researchers examined the fish intake and melanoma risk of more than 490,000 adults across the United States, with an average age of 62. These individuals all participated in the NIH-AARP Diet and Health Study between 1995 and 1996, reporting on how frequently they ate fried fish, non-fried fish, tuna, and their portion sizes over the previous year. The study then followed these adults for another 15 years, keeping track of how many developed skin cancer.
Over the course of the study, 5,034 participants (1.0%) developed malignant melanoma and 3,284 (0.7%) developed “stage 0 melanoma” — abnormal cells on the outer layer of their skin only.
Compared to adults eating about three grams of fish each day, people consuming over 42 grams daily had a 22-percent higher risk of developing malignant melanoma. Participants consuming an average of 42.8 grams of fish per day also had a 28-percent higher risk of developing stage 0 melanoma.
For reference, a standard portion of fish is roughly 140 grams of cooked fish — meaning that eating just one-third of a fish dinner each day may significantly increase melanoma risk.
Fish doesn’t have to be fried to increase cancer risk
Specifically, the team found people averaging about 14 grams of tuna each day had a 20-percent higher risk for malignant melanoma than those averaging just 0.3 grams per day. Similarly, those eating 17.8 grams of non-fried fish per day had an 18-percent higher risk of developing melanoma and a 25-percent higher risk for stage 0 melanoma.
Interestingly, researchers did not find a strong link between fried fish consumption and higher cancer risks. So, what’s causing this potential link to cancer?
“We speculate that our findings could possibly be attributed to contaminants in fish, such as polychlorinated biphenyls, dioxins, arsenic and mercury. 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,” Cho says.
Study authors note that their findings are only observational, meaning they can’t definitively link eating more fish to more cases of skin cancer. The study also did not account for other factors which contribute to melanoma, including mole count, hair color, sunburn history, and other sun-related habits.
However, they did account for each participants’ body mass index (BMI), physical activity, smoking history, alcohol intake, and their family’s history of cancer.
The study is published in the journal Cancer Causes & Control.