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15th June 2022
A higher fish intake appears to be associated with a greater risk of developing both malignant and in situ melanoma according to the results of a prospective cohort study by a group of US researchers.
Melanoma of the skin is the 17th most common cancer worldwide and in 2020, there were an estimated 325 000 new cases and 57 000 deaths. Although a family history and sun exposure have become well recognised as risk factors for the development of a melanoma, dietary factors may also play an important role. For example, caffeine intake may have beneficial and protective effects against cutaneous malignant melanoma, while higher citrus fruit intake and alcohol consumption may have a detrimental effect. Furthermore, while some data point to a diet rich in omega-3 fatty acids as being protective against melanoma, other work has found no such beneficial effect. However, one study has suggested that a higher fish intake is associated with a higher risk of melanoma though the data supporting this was not provided in the paper.
For the present study, the US team used data generated by the US National Institute of Health (NIH)-AARP Diet and Health Study and sought to determine the relationship between a higher fish intake, as well as the type of fish and the risk of melanoma. The NIH-AARP cohort study collected data on fish intake as part of a food-frequency questionnaire and which was differentiated as fried fish, fish sticks, non-fried fish or sea-food and canned tuna. For the present study, the researchers determined the total fish intake as the sum of fried fish, non-fried fish and tuna intake. Using regression analysis, the researchers adjusted for several factors such as body mass index, age, gender, family history of cancer etc and categorised total fish into in quintiles, with the first quintile representing < 5.6 g/fish/day and the fifth > 28.3 g/fish/day.
Higher fish intake and the development of melanoma
A total of 491,367 individuals with a median baseline age of 62 years (59.6% male) were followed for a median of 15.5 years. During the period of follow-up, there were 5,034 cases of malignant melanoma and 3,284 melanoma in situ.
In fully adjusted models, when comparing the lowest to highest intake of fish, there was a significantly increased risk for malignant melanoma (Hazard ratio, HR = 1.22, 95% CI 1.11 – 1.35) and for melanoma in situ (HR = 1.28, 95% CI 1.13 – 1.44).
When analysing the type of fish, the risk of malignant melanoma was elevated for the highest intake of tuna (HR = 1.20) and non-fried fish (HR = 1.18) although there was significantly lower risk for the highest intake fried fish (HR = 0.90, 95% CI 0.83 – 0.98). This pattern was also true for melanoma in situ.
The authors suggested that these results could be explained by the contamination of fish by polychlorinated biphenyls, dioxins etc. While they could not offer any direct proof to support this hypothesis, there is some research which shows a direct association between dietary polychlorinated biphenyls and risk of melanoma.
They concluded that future studies were needed to replicate these findings and to identify the components of fish responsible for the observed associations.
Li Y et al. Fish intake and risk of melanoma in the NIH-AARP diet and health study Cancer Causes Control 2022