Can eating fish increase the risk of cancer?

A study questions whether people who eat a lot of fish have a higher risk of the skin cancer melanoma.

If you’re trying to stick to a healthy diet, fish is a good choice, right? After all, fish is high in protein, low in saturated fat, and a good source of omega-3 fatty acids, vitamin D, and many other nutrients. Eating more fish can mean eating fewer foods with unhealthy fats and higher calorie counts. Indeed, nutritionists commonly recommend more seafood (and fewer cheeseburgers) to improve your diet, and nutrition guidelines promote fish as part of a healthy diet.

So it seems surprising that a new study in Cancer Causes and Control suggests a link between eating fish and skin cancer, especially since the biggest known risk factor for melanoma isn’t food — it’s sun exposure. Having five or more sunburns in your lifetime doubles your risk of developing melanoma.

A study links frequent fish eating to a higher risk of melanoma

Melanoma, the most serious type of skin cancer, is responsible for more than 7,500 deaths in the US each year. And the cases are increasing.

In the new study, researchers found a higher risk of melanoma in people who ate more fish. This study is among the largest and best-designed to examine this link. Nearly 500,000 people in six US states completed a dietary questionnaire in 1995 or 1996. The average age of the participants was 61 years and 60% were male. More than 90% were white, 4% were black, and 2% were Hispanic.

Over the next 15 years, researchers calculated how many people developed melanoma and found that:

  • Melanoma rates were 22% higher among people who reported eating the most fish (about 2.6 servings per week) compared with those who ate the least (0.2 servings per week, or about one serving every five weeks). Similar trends were observed for tuna intake.
  • The risk of precancerous skin changes (called melanoma in situ) was similarly increased among those in the group that ate the most fish.
  • Interestingly, the researchers found no increased risk of melanoma in those who ate the most fried fish. This is surprising because, if eating fish increases the risk of melanoma as the study suggests, it is not clear why frying the fish would eliminate the risk.

Does this mean that eating fish causes melanoma?

No, there isn’t. It is too early to draw definitive conclusions about the relationship between fish in our diet and melanoma. The study had important limitations, including

  • Type of study. Observational studies like this one can reveal a possible link between diet and cancer, but they can’t prove it.
  • Reliance on self-reported survey data. People self-reported how many servings of fish they ate each week, which may not be accurate. Also, the researchers assumed that the fish consumption reported in the original study continued for 15 years, which may not have been the case.
  • Accounting for other factors. Many factors influence the risk of melanoma, such as different sun exposure depending on where the participants lived. The analysis accounted for several key factors, however the study did not gather information about sun exposure, previous sunburns or sunscreen use – all important in melanoma risk. Nor did the researchers ask about skin type or the number of moles; Fair skin or a greater number of moles increase the risk of melanoma.
  • Pollutants. Mercury or arsenic in fish may be to blame for its association with melanoma. This study did not record pollutants, but previous studies have linked mercury exposure to the risk of skin cancer, including melanoma.
  • Lack of diversity. It’s not clear whether the findings apply broadly to people in different racial and ethnic groups, because nine out of 10 study participants were white.

Are some fish safer to eat than others?

The study did not investigate this question. However, if contaminants such as mercury in fish are responsible for the increased risk of melanoma, the FDA offers advice on which fish are safest to eat, especially for children and those who are pregnant or breastfeeding.

However, even if fish is confirmed as a contributor to melanoma risk, other positive effects of fish consumption (such as cardiovascular benefits) may outweigh this risk.

After all

The researchers responsible for this study do not recommend a change in the amount of fish people eat. More study is needed to confirm the findings, to investigate which types of fish affect melanoma risk, and to determine whether certain pollutants in fish are responsible for any increased risk.

Meanwhile, fish with lower levels of mercury (such as salmon and shellfish) remain better dietary choices than the high-fat, highly processed foods typical of many Western diets.

If you plan to spend a lot of time outside this summer, limiting your sun exposure and using sunscreen will likely have a bigger impact on your skin health and overall health than avoiding seafood.

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