The American Heart Association as well as the National Health Service advises eating two servings of fish weekly to reduce the risk of heart disease. Most people recognize fish as a nutritious food. However, new research suggests this amount could be raising the risk of malignant melanoma, the deadliest form of skin cancer. Research done at Brown University discovered that people whose regular daily fish intake was 42.8 grams, which equates to roughly 300 grams per week, had a 22% higher risk of malignant melanoma compared to those whose fish intake was only 3.2 grams. Individuals consuming more fish also had a 28% higher risk of developing abnormal cells in the outer skin layer -- considered stage 0 melanoma or melanoma in situ. These cells are also called pre-cancer.The results published in the Journal of Cancer Causes and Control, were based on a study of 491,367 US adults.Subjects in the study were age 62 (on average) and stated how often they consumed fried fish, non-fried fish, and tuna over the previous year including the serving sizes.Scientists then calculated the frequency of new melanoma cases that cropped up over 15 years utilizing data from cancer registries.Researchers considered other factors that could impact the results, including the subject’s weight, smoking status, alcohol consumption, diet, family history of cancer, and average UV radiation levels in their community, which is considered sun exposure, a known risk factor for skin cancer.Overall, 5,034 people (1% of study participants) developed malignant melanoma during the study period and 3,284 (0.7%) developed stage 0 melanoma.When looking at the results, total fish intake was associated with higher cancer risks. In people who typically consumed tuna, 14.2 grams was linked with a 20% higher risk of malignant melanoma versus those who ate 0.3 grams of tuna. Non-fried fish intake of 17.8 grams per day was linked with an 18% higher risk of malignant melanoma and a 25% higher risk of stage 0 melanoma compared to consumption of only 0.3 grams.Ironically, no significant link was discovered between fried fish intake and skin cancer risk.Prior research had been inconsistent, according to author Eunyoung Cho. "Our findings have identified an association that requires further investigation.”Cho believes their results could be related to contaminants in fish including 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.He notes that his study didn’t evaluate the concentrations of the mentioned contaminants in the subjects’ bodies, so more research is necessary to confirm the connection. Limitations of the study include that the researchers hadn’t accounted for other risk factors for melanoma including mole count, hair color, history of severe sunburn, use of sunscreen, and sunbathing habits.In addition, average daily fish consumption was calculated at the start of the study and may not reflect how much individuals ate over their lifetime. Dr Michael Jones, senior staff scientist in genetics and epidemiology at the Institute of Cancer Research in London said: "The authors found a higher intake of non-fried fish and tuna was associated with melanoma. These results were statistically significant and therefore unlikely due to chance."He notes that it’s possible that individuals who consume more non-fried fish or tuna may have other health habits that raise their risk of melanoma. Confounding factors were considered and adjusted for in the study.As this is an observational study and not a randomized control trial, there may be other factors that researchers had not adjusted for or didn’t adjust for well enough. More research is needed to see if the results of this study can be repeated in other populations and countries where contaminant levels may be different.The results of this study should not change the recommendation to include fish as part of a healthy balanced diet. The authors note that while the contaminants in fish could raise skin cancer risk, they’re likely to raise the risk of other cancers as well. A clear reason why fish intake raises the risk of skin cancer was not discovered and there isn’t clear evidence that consuming fish can lead to a higher risk of skin cancer development.Researchers remind us that, “Eating two portions of fish per week... can be a way of including important nutrients such as omega-3 fatty acids as part of a healthy diet and this study should not discourage people from including fish as part of a healthy diet."What should you tell your clients?

1. Take a look at overall lifestyle habits and risk for skin cancer. Get moles checked, don’t smoke, and wear sunscreen. 
2. Keep servings of fish consumed within reason. The AHA suggests 6 ounces of fish per week (two servings).
3. Choose small, less predatory fish. These include cod, haddock, tilapia, flounder, and trout. 
4. Consume other lean proteins such as skinless poultry or low-fat cuts of pork.
5. Go meatless! Include more beans, lentils, and legumes in your diet instead of animal-based protein.
6. Include more fruits and vegetables to lower the risk of various cancers.
7. Obtain omega-3-fatty acids through chia seeds, ground flaxseed, and walnuts.
8. Obtain adequate vitamin D in food or supplements.

By Lisa Andrews, MEd, RD, LDReference:Li, Y., Liao, L.M., Sinha, R. et al. Fish intake and risk of melanoma in the NIH-AARP diet and health study. Cancer Causes Control 33, 921–928 (2022). https://doi.org/10.1007/s10552-022-01588-5