A novel study hints at a surprising link between eating fish and skin cancer

Eating fish has long been considered a healthy thing to do but a new study is causing people to reconsider this long-held belief. Research has found that eating more fish may be linked to higher skin cancer risks, according to a media release published on Thursday.

An association that requires further investigation

"Melanoma is the fifth most common cancer in the U.S.A., 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 people1. Although fish intake has increased in the U.S.A. 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," said in the statement Eunyoung Cho, the study's corresponding author.

Researchers from Brown University and the National Cancer Institute followed the eating habits of 491, 367 older Americans aged 50-71 over 15 years to evaluate how many of them developed melanoma, an aggressive form of skin cancer in response to high fish consumption. The findings indicated that participants who ate about two servings of fish per week, on average, had a 22 percent higher risk of developing melanoma and a 28 percent higher risk of developing abnormal skin cells that could be a precursor to cancer than people who ate less than half a serving.  

Contaminants in fish

"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," added Cho.

The researchers warn that they did not take into account some risk factors for melanoma, such as mole count, hair color, history of severe sunburn, and sun-related behaviors in their study. In addition, the participants' daily fish intake was calculated at the beginning of the research and could have evolved to change over the 15 years that the subjects were followed and evaluated.

All of these elements could result in inaccurate or faulty results so the researchers made a note that they do not recommend any changes to fish consumption at the moment and that the sun remains the dominant cause of skin cancer.

"It is quite well established that sun exposure increases the risk of skin cancer including melanoma. My paper on fish intake and melanoma is one of the first studies which report that higher fish intake is associated with increased melanoma risk. There should be more studies from different populations to support similar findings.  Until then, I wouldn't make any dietary recommendations," Cho told IE.

Still, the work is a first step to understanding the link between fish consumption and skin cancer, one that further studies down the line may prove to be indisputable. 

The results of the study were published in the journal Cancer Causes & Control.

Abstract:
Prior epidemiological studies evaluating the association between fish intake and melanoma risk have been few and inconsistent. Few studies distinguished different types of fish intake with risk of melanoma. We examined the associations between intake of total fish and specific types of fish and risk of melanoma among 491,367 participants in the NIH-AARP Diet and Health Study. We used multivariable-adjusted Cox proportional hazards regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). During 6,611,941 person-years of follow-up with a median of 15.5 years, 5,034 cases of malignant melanoma and 3,284 cases of melanoma in situ were identified. There was a positive association between higher total fish intake and risk of malignant melanoma (HR = 1.22, 95% CI = 1.11–1.34 for top vs. bottom quintiles, ptrend = 0.001) and melanoma in situ (HR = 1.28, CI = 1.13–1.44 for top vs. bottom quintiles, ptrend = 0.002). The positive associations were consistent across several demographic and lifestyle factors. There were also positive associations between tuna intake and non-fried fish intake, and risk of malignant melanoma and melanoma in situ. However, fried fish intake was inversely associated with risk of malignant melanoma, but not melanoma in situ. We found that higher total fish intake, tuna intake, and non-fried fish intake were positively associated with risk of both malignant melanoma and melanoma in situ. Future studies are needed to investigate the potential biological mechanisms underlying these associations.