Environmental Protection

Study: Selenium Protects Body from Mercury Toxicity

After years of extensive research, the Energy & Environmental Research Center at the University of North Dakota announced that results of environmental, laboratory, and human studies show that mercury levels in freshwater and ocean fish are not as harmful as previously thought.

Current fish advisories may be misleading and should be revised, taking the benefits of selenium into account.

The findings come from two major reports released in the journals Environmental Science & Technology and EcoHealth, both indicating that failure to consider selenium in relation to mercury levels in freshwater and ocean fish will result in critical mistakes in interpretation that generate unreliable and potentially inaccurate advice regarding fish consumption and is deterring people from eating a nutritious product. Both reports state that the effects of mercury exposure are entirely dependent on the amount of selenium present in the diet.

“Selenium is an essential nutrient in healthy brain development and protects the brain from oxidative damage,” said Nick Ralston, an EERC research scientist involved with the studies. “More importantly, selenium protects the body from mercury’s negative effects. The more selenium in the tissue, the less mercury toxicity occurs. Since fish in some areas have much higher levels of selenium than mercury, the consumer receives the healthy benefits of selenium and a natural defense against mercury,” he said.

Results from the first study, conducted jointly by the EERC, the U.S. Environmental Protection Agency Western Ecology Division, and the University of Missouri’s Nuclear Reactor Center, show that an estimated 97 percent of the freshwater fish from lakes and rivers in the western United States are safe to eat. Conducted in 12 states in the western United States, it is the only study of this magnitude that has measured both mercury and selenium in fish tissue.

“The study examined 468 freshwater fish representing 40 species and found that fish from most regions of the country contained more selenium than mercury and so consumers are protected against mercury toxicity,” said Ralston.

The study also discovered that a very small fraction of fish contained more mercury than selenium and might pose a greater mercury toxicity threat than otherwise expected. Human and wildlife populations with poor dietary selenium intake will be especially vulnerable to mercury exposure from eating fish from bodies of water with inadequate selenium resources.

The second major study conducted, funded by the National Oceanic and Atmospheric Administration and EPA, examined a new seafood safety criteria known as the Selenium-Health Benefit Value (Se-HBV), which is specifically designed to be the first step in accurately predicting both the risks and benefits of eating various forms of seafood. Foods that contain large amounts of mercury relative to selenium have negative Se-HBVs, and foods rich in selenium have positive Se-HBVs.

Human studies consistently show that mercury’s toxic effects are directly proportional to mercury–selenium ratios in the foods consumed. Since studies have found that foods with negative Se-HBVs are very dangerous during pregnancy, these foods should be avoided.

“Most varieties of ocean fish have highly positive Se-HBVs between 20 and 200, and recent studies show that mothers who eat these types of ocean fish improve their children’s IQ by up to 10 points,” Ralston said.

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