Researchers recommend revisions to current fish consumption advisories, to account for the protective power of the selenium abundant in most seafood and many freshwater fish 07/23/2009
But we've stepped into the fray because there's been way too much heat... and not enough light... surrounding the emotionally fraught subject of fish and mercury.
Too often, both sides cherry-pick and mischaracterize the evidence... though eco and consumer advocates have typically done the worst distorting.
In fact, the evidence shows that virtually all seafood delivers big health rewards at every age... and poses virtually no risks at any age (see the joint EPA-FDA guidance for the few exceptions).
We're dismayed when these folks raise wildly exaggerated mercury alarms and fail to mention the well-documented need for healthier protein sources in people's diets: primarily fish, plant foods, and high-omega-3 eggs (plus a bit of grass-fed meat or poultry).
Now, leading researchers in the field have published two separate studies... funded by the U.S. EPA and other federal agencies... in which they propose a new, scientifically sounder measure of seafood safety, called the Selenium-Health Benefit Value or Se-HBV.
And with very few exceptions, the studies show that almost all of the ocean fish commonly sold in stores contain enough selenium to neutralize the mercury they contain.
Click here to view a selenium-mercury chart (scroll down to page 6) from the Western Pacific Regional Fishery Management Council, which includes 15 Pacific species (all caught near Hawaii), including four major tuna types, swordfish, mako shark, wahoo, and some uncommon Pacific species.
As you'll see, all but mako shark are higher in selenium than mercury, with swordfish having equivalent selenium and mercury levels.
These rankings make it clearer than ever that ocean fish are substantially safer than their mercury content implies .. especially since the authors of previous human studies found safe, protective selenium-mercury ratios in almost all ocean fish that people ate.
The list of 15 recently tested fish includes yellowfin, skipjack, bigeye, and albacore tuna. In addition to having a very safe selenium-mercury ratio, our troll-caught albacore is unusually low in mercury, due to its age and size. Skipjack is very commonly used in national brands of canned "light" tuna.
Despite the new findings, it still makes sense for younger children and pregnant/nursing women to follow the joint EPA-FDA guidance on consuming the few species relatively high in mercury... some of whose safety ratings could change under the new standard (e.g., swordfish has a high selenium-mercury ratio).
Nuanced new selenium-focused standard fits the evidence
The authors' proposed Selenium-Health Benefit Value safety standard incorporates both the absolute and relative amounts of selenium (chemical symbol Se) and elemental mercury (chemical symbol Hg) in fish or shellfish.
Rodents metabolize selenium and mercury exactly as humans do, and in them, selenium is proven to protect against mercury very effectively.
And the selenium-mercury ratios of the fish and marine mammals eaten by people in the major human population studies predicted their outcomes perfectly.
Children participating in the only studies showing (slight) evidence of possible harm from seafood-heavy diets... which were conducted in New Zealand the Faroe islands... ate lots of shark and pilot whale, which have high mercury-selenium ratios (See our "New paper refutes..." sidebar).
No doubt, it will take time for folks to relinquish the current, scientifically dubious view of seafood safety with regard to mercury... but the human and animal evidence now weighs quite heavily on the side of the proposed change to the proposed Selenium-Health Benefit Value safety standard.
Here's the relevant press release issued by the Energy & Environmental Research Center (EERC) at the University of North Dakota (EERC 2009):
University of North Dakota Press Release, June 22, 2009
EERC Research Finds Mercury Levels in Freshwater and Ocean Fish Not as Harmful as Previously Thought
GRAND FORKS—The Energy & Environmental Research Center (EERC) at the University of North Dakota announced today that after years of extensive research, 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 Dr. 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 (EPA) Western Ecology Division, and the University of Missouri's Nuclear Reactor Center, show that an estimated 97% 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.
Similarly, fear about the potential health risks associated with consuming mercury from ocean fish and shellfish has prompted advisories intended to limit the amount of fish that women eat during pregnancy.
The second major study conducted, funded by the National Oceanic and Atmospheric Administration (NOAA) 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.
Very few seafoods have negative Se-HBVs, but current policies and regulations are based on studies that involved rare types of seafoods, tracking mothers who either ate pilot whales or large sharks, both of which have negative Se-HBVs ranging from 10 to 100.
“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.
Therefore, seafood safety criteria based on Se-HBV will improve public health by properly restricting consumption of hazardous seafoods such as pilot whale and shark, while at the same time encouraging mothers to eat the right types of fish that optimize their nutrition and enhance the IQs of their children.
"The EERC is recognized as the worldwide leader in research on the impacts of mercury on the environment," said EERC Director Gerald Groenewold. “The findings from both of these studies are phenomenal. These findings are critical to developing accurate advisories for fish consumption so that people continue to receive the practical health benefits of eating fish.”
We hope this new evidence and proposal help bring sanity back to the debate over seafood risks and rewards!
- Choi AL, Budtz-Jørgensen E, Jørgensen PJ, Steuerwald U, Debes F, Weihe P, Grandjean P. Selenium as a potential protective factor against mercury developmental neurotoxicity. Environ Res. 2008 May;107(1):45-52. Epub 2007 Sep 12.
- Energy & Environmental Research Center, University of North Dakota (EERC). EERC Research Finds Mercury Levels in Freshwater and Ocean Fish Not as Harmful as Previously Thought. June 22, 2009. Accessed at http://www.undeerc.org/news/newsitem.aspx?id=343
- Peterson SA, Ralston NV, Peck DV, Van Sickle J, Robertson JD, Spate VL, Morris JS. How might selenium moderate the toxic effects of mercury in stream fish of the western U.S.? Environ Sci Technol. 2009 May 15;43(10):3919-25.
- Ralston NV, Blackwell JL 3rd, Raymond LJ. Importance of molar ratios in selenium-dependent protection against methylmercury toxicity. Biol Trace Elem Res. 2007 Dec;119(3):255-68.
- Ralston NV, Ralston CR, Blackwell JL 3rd, Raymond LJ. Dietary and tissue selenium in relation to methylmercury toxicity. Neurotoxicology. 2008 Sep;29(5):802-11. Epub 2008 Aug 9.
- Ralston NV. Selenium health benefit values as seafood safety criteria. Ecohealth. 2008 Dec;5(4):442-55. Epub 2009 Apr 14.