THURSDAY, June 9, 2022 (HealthDay News) — You’ve been adding fish to your diet for a healthy diet, but now a new study delivers bad news: Fish lovers may have a slightly increased risk of melanoma.
Researchers followed more than 490,000 older Americans and found that the 20% with the highest intake had about a quarter higher risk of developing the disease over 15 years, compared with the 20% with the lowest fish consumption.
Still, experts emphasized that the findings merely correlate and cannot blame seafood.
An oncology dietitian who was not involved in the study emphasized the “bigger picture.”
In general, fish is a healthy source of protein, often rich in anti-inflammatory omega-3 fatty acids, said Amy Bragagnini of Mercy Health Lacks Cancer Center in Grand Rapids, Michigan.
Because of its benefits — including links to better heart and brain health — experts generally recommend that people aim for two 4-ounce servings of fish per week, noted Bragagnini, who is also a spokesperson for the Academy of Nutrition. and Dietetics.
Fish could be a “great alternative,” she said, for people who want to limit red and processed meats — which are linked to higher risks of certain cancers, including colon and rectal cancers.
So why would fish be associated with melanoma, a disease most closely linked to risk factors such as sunburn and family history?
It’s not clear, said lead researcher Eunyoung Cho. But one hypothesis is that not the fish, but contaminants — such as mercury and PCBs — may be in relatively high levels in some fish.
Previous research has linked mercury exposure to a higher risk of melanoma and other skin cancers, noted Cho, an associate professor at Brown University’s Warren Alpert Medical School, in Providence, RI.
But, she said, the pollution theory is just that. “This is the first study to show this association,” Cho said. “We need more research to replicate these findings before we can make dietary recommendations.”
The findings, published June 9 in the journal Cancer Causes and Control, are based on 491,000 Americans ages 50 to 71 who were followed for 15 years. Initially, they completed questionnaires about diet, exercise, and smoking and drinking habits.
During the study period, just over 5,000 participants were diagnosed with malignant melanoma, while nearly 3,300 developed melanoma in situ — where “precancerous” melanoma cells reside on the top layer of skin but have not penetrated the deeper layers.
Cho’s team found that people in the top 20% for fish intake had a 22% greater risk of malignant melanoma and a 28% higher risk of melanoma in situ, compared with participants who ate the least fish. That top group usually swallowed almost 43 grams of fish a day.
Those higher risks existed when the researchers took into account other lifestyle habits, race, education level and where people lived.
However, the study lacked details about people’s personal sun habits, said Dr. William Dahut, chief scientific director of the American Cancer Society. It’s not clear, he noted, whether fishing enthusiasts were more likely to own a “beach house” or otherwise spend time outdoors.
Dahut, who was not involved in the study, called it “interesting” and worth delving deeper into.
“But I wouldn’t tell people not to eat fish because of the risk of melanoma,” he said.
Dahut also pointed to a puzzling finding: People who reported eating more uncooked fish or canned tuna had an increased risk of malignant melanoma. But those who ate a lot of fried fish actually had a reduced risk.
Both Cho and Bragagnini agreed that the finding is difficult to explain. It’s possible, Cho speculated, that the type of fish matters; she said future studies could look at whether certain fish species are linked to a higher melanoma risk.
For now, Bragagnini recommended focusing on the general diet, including getting plenty of plant foods like vegetables, fruits, beans, nuts, and high-fiber grains. As for fish, she recommended baking or steaming it rather than frying it, which can deplete the “good” fats.
When it comes to malignant melanoma, Dahut said the primary prevention tactics remain the same: limiting exposure to ultraviolet rays — from the sun or tanning beds — and checking the skin for new growths or changes to existing moles.
The American Cancer Society has advice on diet and lifestyle.
SOURCES: Eunyoung Cho, ScD, associate professor, dermatology, Warren Alpert Medical School of Brown University, Providence, RI; Amy Bragagnini, MS, RD, oncology dietitian, Mercy Health Saint Mary’s Campus, Lacks Cancer Center, Grand Rapids, Michigan, and spokesperson, Academy of Nutrition and Dietetics, Chicago; William L. Dahut, MD, scientific director, American Cancer Society, Atlanta; Cancer Causes and ControlJune 9, 2022