Increased fish consumption may be associated with skin cancer risk, study finds

22 Jun 2022 --- A study led by the US-based Brown University School of Public Health has revealed increasing overall fish consumption is associated with a higher risk of melanoma development – an aggressive form of skin cancer. However, the European Food Information Council (EUFIC) addresses the study’s limitations, stating that the investigation is observational and cannot prove a direct cause and effect.

The current study examined data from the NIH-AARP Diet and Health Study to better understand the connection between nutrition and health. The researchers looked at the associations between intake of total fish and specific types of fish and the risk of melanoma among 491,367 participants in this study.

The analysis revealed that a greater intake of total fish, tuna and non-fried fish was positively correlated with the risk of both malignant and in situ melanoma – when the cancer cells are in the epidermis.

“The study doesn’t impact nutritional guidelines for fish intake,” Laura Bosman, content production at EUFIC, tells NutritionInsight.

“The authors hypothesize that contaminants in fish (such as mercury, polychlorinated biphenyls, dioxins and arsenic) may explain their results, yet the amounts of these contaminants in the participants’ bodies were not assessed, and therefore this hypothesis cannot be validated by the data.”

The researchers note that future research is required to learn more about potential biological pathways that may underlie these correlations.

Analyzing fish intake and melanoma correlation
The study followed the participants’ food intake for approximately 15 years. During this period, 5,034 cases of malignant melanoma and 3,284 cases of melanoma in situ were identified.

The researchers observed a positive association between higher total fish intake and risk of malignant melanoma and melanoma in situ.

Consuming two servings of fish each week may raise the danger of developing malignant melanoma.Additionally, 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 the risk of malignant melanoma and melanoma in situ.

However, fried fish intake was inversely associated with the risk of malignant melanoma, not melanoma in situ.

Study limitations
According to EUFIC, the study cannot prove that increased fish intake causes melanoma as observational studies can’t prove direct cause and effect.

The study has taken into account multiple health and lifestyle factors such as age, ethnicity, family history of cancer, physical activity, smoking, alcohol and ultraviolet (UV) exposure from the sun, which could potentially influence the melanoma outcome.

Additionally, EUFIC adds that the estimates of fish intake may be inaccurate as food frequency questionnaires have limitations. Typical intake, portion size and preparation may be difficult to estimate accurately and include subjective interpretations that vary between individuals. 

Neither does the food frequency questionnaire represent lifetime dietary patterns. Also, the analysis didn’t assess relevant nutritional details such as how fish was prepared – if it was battered or deep-fried – nor made a distinction between oily and non-oily fish categories.

Fishy risks
The baseline risk of melanoma remains relatively low. EUFIC adds that this is the case as the study communicates relative risks, not absolute ones.

The relative risk displays the increased risk of melanoma in the high fish eaters group compared to the low fish eaters’ group. However, the estimated lifetime risk of developing malignant melanoma (the absolute risk) is around 1% to 2% of the total participants in the study. 

The cells (known as melanocytes) that regulate the skin’s pigment give rise to malignant melanoma. With the added 22% relative risk increase in the high fish-eating group, this would mean that the absolute risk would increase to 1.2-2.4%, thus remaining reasonably small.

EUFIC stresses that any risk from a high fish consumption remains smaller than the leading risk factors for melanoma, mainly excessive sun exposure.

Contaminants’ role
EUFIC adds that the link between two portions of fish per week is the recommended consumption amount by the National Health Service of England (NHS).

The recommended consumption is at least two portions of fish per week (including one of oily fish), with a portion weighing around 140 g. The observed 22% increased risk among participants with the highest daily fish intake equal to just over two portions per week.

However, fish, particularly oily fish, has been associated with many health benefits, including cardiovascular benefits. These benefits may outweigh any small risk increase.

Lastly, the EUFIC adds that contaminants may explain increased melanoma risk in fish. The study authors caution that contaminants in fish, such as mercury, and not the fish itself, likely play a role in the cancer association.

“We need further research to clarify the relationship between the contaminants in fish that could contribute to the observed association between fish intake and melanoma risk and any underlying biological mechanisms,” says Bosman.

Attempts to tackle skin cancer
Separate research presented at the European Academy of Dermatology and Venereology unveiled that vitamin B3 consumption may help shield skin cells from the effects of UV radiation, potentially preventing skin cancer.

Additionally, according to a UK-based University of Leeds study, vitamin D helps decrease the growth and spread of melanoma.

By Nicole Kerr