Too much mercury or too little selenium? Fishing for answers.

Sep 19, 2008

Ralston VC, CR Ralston, JL Blackwell III and LJ Raymond.2008. Dietary and tissue selenium in relation to methylmercury toxicity. NeuroToxicology online Aug 9, 2008.

Synopsis by Niladri Basu

Scientists show that comparing mercury and selenium levels in fish provides a more accurate way to assess mercury's toxic effects than reporting mercury alone, highlighting the need to consider both when eating fish. Mercury and selenium, an essential nutrient, act against each other.

New research suggests that the presence of mercury in fish should worry us less than the absence of selenium. Mercury is a potent neurotoxin. Selenium is an essential nutrient with many beneficial properties. The scientific establishment has long believed that selenium counteracts mercury neurotoxicity. But a growing number of scientists are considering the alternate scenario – that mercury counteracts selenium’s benefits. In this unique study on laboratory rats, researchers assessed the health effects of selenium (low, medium, high levels) in the absence and presence of mercury (low and toxic levels). They tried to mimic a typical human exposure scenario. The researchers found that comparing the selenium-mercury ratio is a better predictor of neurotoxicity than mercury alone. This finding sheds new and important information on the true health benefits and risks of fish consumption. Future studies should report selenium values alongside mercury levels.