ISLAMABAD, (ONLINE): Greater consumption of tuna and other non-fried fish was associated with an increased risk of melanoma, the most serious type of skin cancer, according to a new study.
Researchers suspect this link may be due to toxins rather than the fish itself.
“We speculate that our findings could possibly be attributed to contaminants in fish, such as polychlorinated biphenyls, dioxins, arsenic and mercury,” study author Eunyoung Cho, ScD, an associate professor of dermatology and epidemiology at Brown University, said in a news release.
However, the researchers caution against making any changes to your fish consumption, saying more research is needed to better understand the link seen in the study.
Certain fish linked to higher melanoma risk
Although melanoma accounts for only a small fraction of skin cancers, it causes the vast majority of skin cancer deaths, according to the American Cancer SocietyTrusted Source (ACS).
The see if there was a link between melanoma risk and fish consumption, the authors of the new paper analyzed data from over 490,000 adults who took part in the National Cancer Institute’s NIH-AARP Diet and Health Study between 1995 and 1996.
Participants reported how often and how much fish they ate, including fried fish, non-fried fish such as flounder and cod, and canned tuna.
Researchers obtained data from cancer registries to determine how many participants developed melanoma over the next 13 to 16 years.
They also tried to consider other factors that might affect a person’s risk of melanoma, such as body mass index, physical activity level, smoking, family history of cancer, alcohol and calorie intake, and participants’ average local ultraviolet (UV) radiation levels.
Researchers found that people who ate the highest amount of fish per day on average (42.8 grams) had a 22 percent higher risk of malignant melanoma compared to those with the lowest average daily intake (3.2 grams).
They also had a 28 percent higher risk of developing abnormal cells only in the outer layer of the skin; this is known as melanoma in situ.
A serving size of cooked fishTrusted Source is approximately 85 grams, although this varies based on your weight. A standard can of tuna is 142 grams.
In addition, people in the study who ate 14.2 grams of tuna per day on average had a 20 percent higher risk of malignant melanoma and a 17 percent higher risk of melanoma in situ compared to those who ate 0.3 grams per day on average.
For those who ate an average of 17.8 grams per day of non-fried fish, the risk of malignant melanoma was 18 percent higher than those who ate 0.3 grams per day. Their risk of in situ melanoma was also 25 percent higher.
Researchers found no link between fried fish consumption and the risk of either types of melanoma. However, even people who ate the most fried fish had, on average, only 7.1 grams per day.
More research is needed
Previous research looking at the link between fish consumption and melanoma risk has had mixed results, wrote the researchers. Some of these studies, though, were not as rigorous as the current one.
“This [new] study is important because it’s very large and it’s prospective by design, meaning that fish intake was assessed before the development of cancer,” Dr. Cho said.
However, there are several limitations of the new study, which would need to be addressed with future research.
For example, researchers estimated people’s UV exposure based on the average UV radiation levels where they lived. This doesn’t consider how much time they spent in the sun or whether they had additional sun exposure from their job.
Researchers also didn’t have information about other melanoma risk factorsTrusted Source such as how many moles people have, their hair and skin color, or history of severe sunburns.
They also only measured dietary intake, physical activity, and other behaviors at the beginning of the study, but these could have changed over time.
In addition, this is an observational study, so it can’t prove that eating fish causes melanoma, only that there is a link between the two.
This doesn’t mean the results should be ignored.
Fish tissue can contain contaminants such as mercury and polychlorinated biphenyls (PCBs). The levels vary from location to location but can increase in concentration as you move up the food chain, and larger predators tend to have higher levels.
Mercury, PCBsTrusted Source and other toxins are also a potential health hazard for people who consume them.
Don’t pass on the fish
A previous study of more than 20,000 Swedish women found that exposure to PCBs in the diet was associated with a four-fold increased risk of malignant melanoma compared to women who ate the lowest amount of fish.
Researchers in this study also estimated women’s intake of omega-3 fatty acidsTrusted Source. Women with the highest intake of these healthy fats had an 80 percent lower risk of melanoma, even after researchers considered their dietary PCBs exposure.
This fits with another study, which found that people who ate higher amounts of fish had a lower risk of melanoma, and greater fruit and vegetable intake was also linked to a lower risk.
However, neither of these earlier studies or the new study measured the level of mercury, PCBs or other contaminants in participants’ blood.
This step would be needed to tease apart the benefits of fish consumption from the harmful effects of toxins in the fish tissue.
“Our study did not investigate the concentrations of these contaminants in participants’ bodies, and so further research is needed to confirm this relationship,” Cho said.
It’s too soon to change your fish consumption based on this study, especially since fish and other seafood are an excellent source of protein, healthy fats, calcium and vitamin D.
But you can take steps to minimize your exposure to toxins.
“The good news is there are an abundance of low-mercury seafood options to choose,” said Whitney Linsenmeyer, PhD, RD, spokesperson for the Academy of Nutrition and Dietetics and assistant professor of nutrition at Saint Louis University.
These includeTrusted Source anchovy, black sea bass, catfish, cod, flounder, herring, lobster, salmon, sardines, freshwater trout and whiting.
Certain groups are more vulnerable to mercury, which has other better-studied health risks.
“The groups that should be most concerned about mercury levels in fish are people who are pregnant or lactating, those who may become pregnant and young children,” Dr. Linsenmeyer said.
She recommends that these people choose seafood with higher levels of essential fatty acids yet lower mercury levels, such as salmon, anchovies, sardines, Pacific oysters and freshwater trout.