Could eating more fish raise your melanoma risk? – Expert Reaction

People who ate higher amounts of fish – similar to half a can of tuna a day – had a 22% higher risk of melanoma than people who ate much less fish, in a surprise result from a large US study.

The research team speculates that contaminants in fish – like mercury – could possibly explain the link, but they don’t examine that in the study. The authors don’t recommend eating less fish based on this study alone, as they did not take into account some key risk factors for melanoma, including sun-related behaviours.

The SMC asked experts to comment on the recommendations. 

Amanda Oakley, Adjunct Associate Professor, Department of Medicine, University of Auckland; and Dermatologist, Waikato District Health Board, comments:

“This American study of fish intake and risk of melanoma suggests a slightly higher risk of melanoma in patients that consume a lot of fish compared those that don’t. The findings are preliminary and should not influence fish consumption habits in New Zealand.

“Nearly all cases of melanoma in New Zealand can be attributed to exposure to solar ultraviolet radiation. Primary prevention of melanoma must emphasise protection from sunburn and tanning, and minimising time outdoors for people with white skin.

“Early detection of melanoma requires self-skin examination and regular skin checks of those at high risk of melanoma (older people, males, people who have had a previous melanoma or other skin cancer). See your doctor if you find any unusual or changing skin lesions.”

Conflict of interest statement: “I am on MelNet’s board (the Melanoma Network of New Zealand). I am a diagnosing consultant for MoleMap New Zealand.”

Dr Louise Reiche, vocationally registered dermatologist, member and immediate past president of the New Zealand Dermatological Society, comments:

“Melanoma is well recognised to more commonly arise in those who have had high levels of episodic or cumulative occupational or recreational sun (significant carcinogen) exposure, several sunburns, have fair skin, large numbers of moles (particularly irregular moles), positive family history of melanoma, blue eyes, and red or lighter hair colour.

“Cumulative exposure to heavy metals, such as arsenic which was used in many medicinal products last century, is long recognised to increase skin and other cancers later in life.  Habitual holistic sun-protection measures reduce melanoma risk, and healthy lifestyles including low fat and Mediterranean- style seasonal, locally-grown plant-rich diets have also been found to offer some protection.

“This observational NIH-AARP diet and health study showing a statistical association between increasing fish intake and risk of melanoma raised concerns that contaminants in fish, such as polychlorinated biphenyls, dioxins, arsenic and mercury may be contributory, and warrants further investigation in other parts of the world. Polychlorinated Biphenyls (PCBs) were used in a wide range of products such as hydraulic fluids, brake lining components, as ‘plasticisers’, in the production of marine antifouling paints, adhesives, sealants, varnishes, and printing inks.  PCBs are banned in New Zealand under the Hazardous Substances and New Organisms (HSNO) Act.

“The study omitted analysis of many established melanoma risk factors but highlights the need for ongoing research and measures to restore and protect healthy environments – including our oceans and drinking water – to minimise additional carcinogenic exposure risks.

“Meanwhile, New Zealanders are encouraged to sun-protect their skin, and to follow a well-balanced, varied nutritious diet while caring for our environment.”

Conflict of interest statement: “I have represented Melnet, for the Australian /NZ Sunscreen standards 2021, am an executive member for the NZ Dermatological Society (NZDSI), and have worked with the Cancer Society NZ to ban commercial sunbed use in the under-18s, all supporting ways to reduce melanoma risk for NZers.  I am also interested in nutrition and the skin, and ways we can all better care for our environment.”

Note: See also expert comments from Science Media Centres in Australia and the UK.