Selenium counteracts mercury, studies say

19 October 2007

SFB Staff (Oct. 19) — Two recent studies by Dr. Nicholas Ralston, Ph.D., provide further evidence that selenium effectively negates the toxic effects of methylmercury in seafood. Ralston, who heads the Energy and Environmental Research Center at the University of North Dakota in Grand Forks, N.D., told SeaFood Business yesterday that marine fish species, with the exception of shark, are rich in selenium.

"The public needs to know that selenium-dependent enzymes protect the brain against oxidative damage," says Ralston. "All creatures that have nervous systems have selenium-dependent enzymes that protect them. If you have a brain you have selenium-dependent enzymes."

Ralston's work will be published in the December issue of the scientific journal Biological Trace Element Research, which is available online now. The print version will be available soon.

In the study, "Selenium and Mercury in Pelagic Fish in the Central North Pacific Near Hawaii," Ralston and co-author Dr. J. John Kaneko of PacMar in Honolulu found that amounts of selenium exceeded mercury in almost all of the 420 fish they examined, representing 15 pelagic fish species.

"A selenium health-benefit value based on the absolute amounts and relative proportions of selenium and mercury in seafood is proposed as a more comprehensive seafood safety criterion," the study concludes. In other words, the federal seafood mercury advisory should also factor in the powerful counteractive effects of selenium.

In another study published in the same issue, "Importance of Molar Ratios in Selenium-Dependent Protection Against Methylmercury Toxicity," Ralston and his colleagues at EERC discovered that "mercury-to-selenium molar ratios provide a more reliable and comprehensive criteria" for evaluating risks associated with methylmercury exposure.

Ralston, commenting on the controversy surrounding the Oct. 4 recommendation by the National Healthy Mothers, Healthy Babies Coalition that urged pregnant women and nursing mothers to consume at least 12 ounces of seafood per week, says increased fish consumption can only benefit developing fetuses and newborn babies.

"Really, if we spend more time looking at the full spectrum of questions, ocean fish are selenium-rich and are loaded with omega-3 fatty acids. Those two nutrients coming from fish will benefit children," says Ralston. "All ocean fish are rich in selenium, with the exception of shark. Yet most mercury studies have focused on whale or shark [meat] consumption. Shark is not what I consider a typical variety of seafood."

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