A study asks whether people who eat a lot of fish have a higher risk for 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 less of foods with harmful 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, particularly since the biggest known risk factor for melanoma is not dietary –– it’s sun exposure. Having five or more sunburns in your life doubles your risk of developing melanoma.
A study links eating fish often with 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 cases are on the rise.
In the new study, researchers found a higher risk of melanoma among people who ate the most fish. This study is among the largest and most well-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 participants was 61 and 60% were male. More than 90% were white, 4% were Black, and 2% were Hispanic.
Over the following 15 years, the researchers tallied how many people developed melanoma, and found that:
- The rate of melanoma was 22% higher among people reporting eating the most fish (about 2.6 servings per week) compared with those who ate the least (0.2 servings a week, or about one serving every five weeks). Similar trends were noted for intake of tuna.
- The risk of precancerous skin changes (called melanoma in situ) rose similarly among those in the group that ate the most fish.
- Interestingly, researchers found no increased risk of melanoma among those eating the most fried fish. This is surprising because, if eating fish increases the risk of melanoma as the study suggests, it’s not clear why frying the fish would eliminate the risk.
Does this mean eating fish causes melanoma?
No, it doesn’t. It’s too soon to make definitive conclusions about the relationship between fish in our diets and melanoma. The study had important limitations, including
- Type of study. Observational studies like this one can detect a possible link between diet and cancer but cannot 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, researchers assumed that fish consumption reported on the initial survey persisted for 15 years, which may not have been the case.
- Accounting for other factors. Many factors affect risk for melanoma, such as varied sun exposure depending on where participants lived. The analysis did account for some key factors, yet the study didn’t collect information about sun exposure, past sunburns, or use of sunscreen — all important in melanoma risk. Nor did researchers ask about skin type or number of moles; fair skin or higher numbers of moles raise risk for melanoma.
- Contaminants. Mercury or arsenic in fish may be to blame for its link to melanoma. This study did not record contaminants, but previous studies link mercury exposure with the risk of skin cancers, including melanoma.
- Lack of diversity. It’s not clear if the findings apply broadly to people in different racial and ethnic groups, because nine in 10 study participants were white.
Are some fish safer to eat than others?
The study did not explore this question. However, if contaminants like mercury in fish are responsible for increasing the risk of melanoma, the FDA offers advice on which fish are safer to eat, particularly for children and those who are pregnant or breastfeeding.
Yet even if fish is confirmed as a contributor to the risk of melanoma, other positive effects of fish consumption (such as cardiovascular benefit) may far outweigh this risk.
The bottom line
The researchers responsible for this study are not recommending a change in how much fish people eat. More study is required to confirm the findings, investigate which types of fish affect melanoma risk, and determine whether certain contaminants in fish are responsible for any added risk.
In the meantime, fish with lower mercury levels (such as salmon and clams) remain better dietary choices than the high-fat, highly processed foods typical of many Western diets.
If you’re planning to spend a lot of time outside this summer, limiting sun exposure and using sunscreen will likely have a bigger impact on skin health and your overall health than avoiding seafood.
About the Author
Robert H. Shmerling, MD, Senior Faculty Editor, Harvard Health Publishing
Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School. … See Full Bio View all posts by Robert H. Shmerling, MD