With numerous studies showing the clear health benefits of eating fish, especially for omega-3 fatty oils and a wide range of minerals, it comes as shock that new research has suggested that eating more fish may be linked to a greater risk of malignant melanoma.

The results of the study, published on the 9th of June in Cancer Causes & Control, found that people who ate an amount of fish equivalent to about half a can of tuna a day had a risk of melanoma that was one fifth higher than people who ate the equivalent amount of tuna in a month.

Specifically, the risk of malignant melanoma was 22% higher among those whose median daily intake was 42.8 grams, compared to those whose median daily fish intake was 3.2 grams, and people consuming the higher quantity had a 28% increased risk of developing abnormal cells in the outer layer of the skin – melanoma in situ.

The team, from Brown University, also found a link to greater risk of melanoma in people who ate more non-fried fish and tuna – but not in those who ate more fried fish – yet were unable to show that eating fish in any way causes melanoma.

Lead author Eunyoung Cho said that their findings have identified an association that requires further investigation, suggesting that contaminants such as mercury in fish might explain the link.

“We speculate that our findings could possibly be attributed to contaminants in fish, such as polychlorinated biphenyls, dioxins, arsenic, and mercury,” Ms Cho said.

“Previous research has found that higher fish intake is associated with higher levels of these contaminants within the body and has identified associations between these contaminants and a higher risk of skin cancer.

“However, we note that our study did not investigate the concentrations of these contaminants in participants’ bodies and so further research is needed to confirm this relationship.”

Melanoma risk factors such as mole count, hair colour, history of severe sunburn and sun-related behaviours were also excluded from the analysis.

The authors investigated data from 491,367 adults, who had participated in the NIH-AARP Diet and Health Study between 1995 and 1996, accounting for sociodemographic factors, as well as participants’ BMI, physical activity levels, smoking history, daily intake of alcohol, caffeine and calories, family history of cancer, and the average UV radiation levels in their local area.

During the study period, 5,034 participants (1.0%) developed malignant melanoma and 3,284 (0.7%) developed melanoma in situ.