Fish is brain food and good for your health. The evidence is overwhelming that eating ocean fish including tuna is part of a healthy diet and life-style despite the low levels of mercury present. While it is agreed that mercury at high concentrations is toxic, the toxicity of trace levels of
mercury found in open ocean fish like tuna remains undocumented and controversial.

There are 3 major long-term studies of the effects of mercury from seafood consumption on child development. No adverse health impacts were detected in children born to women that ate on average 12 meals of fish per week during pregnancy in the Seychelles Islands. In the UK, children’s testing scores improved with increasing fish consumption by their mothers during pregnancy. Limiting fish consumption (2 meals of fish or less per week) was associated with greater risk of lower developmental scores.

In contrast, a study in the Faroe Islands found diminished test scores in children whose mothers ate fish, but received 90% of their dietary mercury from eating pilot whale meat. The comparison of these 3 studies raises questions about the importance of the food source of mercury and the possibility of other nutritional factors that play a role in determining mercury health risk.

Selenium, an essential trace element may hold the answers. Selenium is vital to the body’s  antioxidant system, proper immune system function, has anticancer effects and is known to interact with metals including mercury. In the early 1970’s, Dr. Howard Ganther and others from the University of Wisconsin first discovered that adding yellowfin tuna to the diet of animals being fed artificially high levels of mercury, protected against, rather than contributed to mercury  toxicity. These results surprised the researchers and led them to conclude that other nutritional elements in tuna were responsible for the protective effects. The likely candidate was selenium. Tuna and other open ocean fish are now known to be rich sources of healthy selenium. But can this explain why mercury in tuna has not been a health problem? What additional research or understanding is needed now to convince a wider spectrum of scientists, medical and health professionals of yet another important health benefit from eating ocean fish, especially tuna? International Symposium on Selenium and Mercury Interaction.

The interactions between dietary selenium and mercury are now the topic of exciting new research. Some of those studies were presented at a recent scientific meeting dedicated to the subject. The First International Symposium on Selenium and Mercury Interactions, was held February 22-24, 2007 in La Jolla, California organized by Dr. Gerhardt Schrauzer of the University of California at San Diego and the International Association of Bioinorganic Scientists (IABS). The symposium assembled scientists from the US, Japan, Spain, Ireland, Slowenia, Denmark and elsewhere to share information on selenium and mercury interactions and health effects. Papers presented during this important symposium will be published in the journal, Biological Trace Element Research.

Of particular interest was a paper given by Dr. Nicholas Ralston of the Energy and Environmental Research Center in North Dakota on the biochemical basis of selenium’s protective effects on mercury toxicity. Selenium has an extremely high binding attraction and strength with mercury, forming a biologically inactive compound, mercury selenide. For this reason it is important to have an excess of selenium over mercury in the diet, or run the risk of selenium deficiency and the toxic effects of mercury.

Dr. Ralston and his colleagues suggest that selenium sequestration by mercury and the impacts on vital selenium-dependent functions may actually be the mechanism of mercury’s toxic effects. His studies demonstrated the protective effects of selenium at levels found ocean fish in mice fed diets laced with methylmercury at levels higher than normally found in ocean fish. The assessment of mercury health risks is incomplete without also considering mercury and selenium interactions and the ratios of available mercury and selenium in the diet.

But how much selenium is in tuna? Dr. John Kaneko of PacMar Inc. in Honolulu, Hawaii presented the results of a recent survey (supported by NOAA) of selenium to mercury molar ratios in pelagic fish caught in the Hawaii longline fishery operating in the central North Pacific Ocean. All tuna species sampled, including bigeye, yellowfin, albacore and skipjack contained a healthy excess of selenium over the mercury content. For this reason, eating tuna, an excellent source of selenium, is more likely to protect against mercury toxicity, than cause it.

By contrast, pilot whale meat from the Faroe Islands contains not only a higher mercury concentration than most ocean fish, but also contains a much greater amount of mercury than selenium. For this reason, pregnant women in the Faroe Islands are now advised to stop eating pilot whale meat during pregnancy to avoid net mercury intake, but to continue to eat fish to provide their children with the health benefits of omega 3 fatty acids and selenium. Tuna is a rich source of high quality protein, omega 3 fatty acids and selenium and should be considered part of a healthy diet. Tuna is health food, its good for your heart and there is growing evidence to support the long held belief that fish is also brain food for children, adults and seniors.

Published in: OPRT NEWSLETTER INTERNATIONAL, May 2007

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