Heavier consumption of fish, including tuna and other non-fried fish, has been associated with a higher risk of melanoma, findings from a large prospective cohort study have found.
Fried fish, meanwhile, which has never been accused of being healthy, was associated with a small though non-significant lower risk for malignant melanoma (HR 0.90, P=0.06 for trend).
The researchers believe the findings could be related to contaminants in the fish, including mercury and arsenic.
MedPage Today reports that examining data on nearly half a million participants from the NIH-AARP Diet and Health Study revealed that people in the highest quintile of total fish intake had a 22% higher risk for malignant melanoma compared with those in the bottom quintile, after multi-variable adjustment that included melanoma-specific risk factors (HR 1.22, 95% CI 1.11-1.34, P=0.001 for trend).
A similarly higher risk was also seen for melanoma in situ (HR 1.28, 95% CI 1.13-1.44, P=0.002 for trend), according to the study from Eunyoung Cho, ScD, of Brown University School of Public Health in Providence, Rhode Island, and colleagues.
“Our findings may be explained by contaminants in fish, such as polychlorinated biphenyls, dioxins, arsenic and mercury,” the group wrote in Cancer Causes & Control. “Higher fish intake is associated with higher level of body burden of each of these contaminants, which are associated with higher risk of skin cancer.”
The associations were consistent across several demographic and lifestyle factors and for both tuna and non-fried fish:
• Tuna, malignant melanoma: HR 1.20 (95% CI 1.09-1.31)
• Tuna, melanoma in situ: HR 1.17 (95 CI 1.05-1.31)
• Non-fried fish, malignant melanoma: HR 1.18 (95% CI 1.07-1.30)
• Non-fried fish, melanoma in situ: HR 1.25 (95% CI 1.11-1.42)
The authors did their best to control for confounding factors, but “technically, it is just rather difficult to adequately control for the most important one – lifetime sun exposure”, Teresa Fung, ScD, RD, Harvard T. H. Chan School of Public Health, told MedPage Today.
Fung said the researchers used geographical ultraviolet radiation (UVR) quantity to approximate sun exposure, and also controlled for physical activity, as people tend to exercise outdoors. “Those were helpful and important, but sun exposure remained inadequately controlled for,” she said.
“I am not alarmed by the results of this study, and there is no need to reduce fish intake. However, for general good nutrition practice, fried fish in the form of fish sandwich (white bread) is generally not a healthy food.”
For their study, Cho’s group examined data from 491,367 participants (ages 50-71) from the NIH-AARP Diet and Health Study, which in 1995-1996 mailed questionnaires to AARP members in six states (California, Florida, Louisiana, New Jersey, North Carolina, Pennsylvania) and two metropolitan areas (Detroit, Atlanta).
People with a history of cancer, who had died, moved out of the study area, or who had an extreme caloric intake (less than 426 kcal or above 6,760 kcal) were excluded from the study. About 90% of the study population were non-Hispanic white.
At baseline, people who consumed higher quantities of fish were more likely to be younger men, with higher education levels, physical activity levels, body mass index, daily caloric intake, and alcohol intake.
Individuals were followed for a median 15.5 years, for a total of more than 6.6m person-years of follow-up. By the end of the study period, there were 5,034 total cases of malignant melanoma and 3,234 cases of melanoma in situ. Median age at diagnosis was 70.8 years.
Other covariates for the multi-variable analysis included age, sex, education, family history of cancer, alcohol intake, smoking history, and daily caloric intake. Fish types included canned tuna, fried fish or fish sticks, or non-fried fish (cod, clams, shrimp, flounder, crabs, etc.).
A limitation of the study included the assumption that dietary and lifestyle habits did not change from participants’ baseline questionnaire, the authors noted. Furthermore, UVR exposure was not estimated based on people’s behaviour. Researchers also lacked data on melanoma risk factors such as mole count, hair colour and history of sunburn.
Fish intake and risk of melanoma in the NIH-AARP diet and health study
Yufei Li, Linda M. Liao, Rashmi Sinha, Tongzhang Zheng, Terrence M. Vance, Abrar A. Qureshi & Eunyoung Cho
Published in Cancer Causes & Control on 9 June 2022
Prior epidemiological studies evaluating the association between fish intake and melanoma risk have been few and inconsistent. Few studies distinguished different types of fish intake with risk of melanoma.
We examined the associations between intake of total fish and specific types of fish and risk of melanoma among 491,367 participants in the NIH-AARP Diet and Health Study. We used multivariable-adjusted Cox proportional hazards regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).
During 6,611,941 person-years of follow-up with a median of 15.5 years, 5,034 cases of malignant melanoma and 3,284 cases of melanoma in situ were identified. There was a positive association between higher total fish intake and risk of malignant melanoma (HR = 1.22, 95% CI = 1.11–1.34 for top vs. bottom quintiles, ptrend = 0.001) and melanoma in situ (HR = 1.28, CI = 1.13–1.44 for top vs. bottom quintiles, ptrend = 0.002). The positive associations were consistent across several demographic and lifestyle factors. There were also positive associations between tuna intake and non-fried fish intake, and risk of malignant melanoma and melanoma in situ. However, fried fish intake was inversely associated with risk of malignant melanoma, but not melanoma in situ.
We found that higher total fish intake, tuna intake, and non-fried fish intake were positively associated with risk of both malignant melanoma and melanoma in situ. Future studies are needed to investigate the potential biological mechanisms underlying these associations.
See more from MedicalBrief archives: