However, other than industrial accidents, the only instances in which humans have been harmed by mercury had nothing to do with eating normal ocean fish:
- Consumption of grains coated with mercury-laced fungicides (Iraq).
- Consumption of fresh water fish contaminated by mercury-laced coal emissions (selected locations worldwide).
- Consumption of fish very heavily contaminated by localized mercury pollution (the famous Minimata Bay incident in Japan).
Mercury, fish, and the fetus
The mercury found in fish comes from natural sources such as volcanoes and from coal-fired power plants.
Much of it ends up in oceans, lakes, and rivers, where it works its way up the food chain into fish and marine mammals.
Ocean fish contain low levels of a well-absorbed form called methyl mercury, which can transfer from pregnant women to their fetus.
The risks of mercury to babies' fast-growing brains stems from the metal's strong chemical attraction to selenium.
Selenium is an essential part of the body's key antioxidant enzymes, and mercury-bound selenium isn't available to create these critical compounds.
Bodies low in selenium cannot control the normal metabolic agents called free radicals … which, if left uncontrolled, will harm your cells … with brain and nerve cells hit first and hardest.
Yet, there are very few documented cases of mercury toxicity from eating ocean fish.
Why are ocean fish so clearly safe and beneficial, despite the fact that they contain low levels of mercury?
Selenium is the key to seafood safety
Almost all ocean fish contain more selenium than mercury, so the body actually gains selenium when you eat these fish.
In contrast, fresh water fish from lakes and rivers lacking selenium and/or polluted by mercury-laced coal emissions can contain more mercury than selenium.
The “selenium hypothesis of seafood safety” is supported by extensive lab research, several clinical studies ... and all of the epidemiological studies that compared the fish intake and mercury levels of mothers, infants, and kids to brain health in childhood and adolescence.
You'll find our many reports on this subject in the Mercury Issues
section of our news archive, and links to relevant websites on the Purity Story page
of our website.
The case for seafood safety just got more support from a study that draws upon more than 30 years of research.
30-year study finds no link between autism and mercury from fish
The Seychelles study is a project of the University of Rochester Medical Center (URMC).
The Republic of Seychelles proved the ideal place to examine the potential health impact of persistent low level mercury exposure.
With a population of 87,000 people spread across an archipelago of islands in the Indian Ocean, fishing is a major industry and seafood is a primary food source.
And it's essential to note that the nation's residents consume 10 times fish than people in the U.S. and Europe.
The Seychelles Child Development Study – a partnership between URMC, the Seychelles government, and Ireland's University of Ulster – was started in the mid-1980s to study the impact of fish consumption and mercury exposure on child development.
URMC-led researchers have now followed mothers and children eating fish-heavy diets in the Republic of Seychelles for 30 years.
Their autism study involved data collected from and about 1,784 children, adolescents, and young adults, and their mothers in the Seychelles.
The researchers gauged the children's prenatal mercury exposure by analyzing hair samples collected from the mothers around the time of birth … which revealed the mercury levels in each woman's body, and in her growing fetus.
The researchers gave parents and teachers standard surveys designed to see how many of the participating children exhibited autism spectrum-like behaviors.
(Although they don't provide a definitive diagnosis, both tests are widely used in the U.S. as an initial screening tool.)
The URMC team compared the mercury levels of the mothers with the test scores of their children.
That comparison detected no link between the extent of a child's prenatal mercury exposure and later evidence of autism.
Importantly, the mercury in the mothers came almost entirely from the copious amounts of selenium-rich ocean fish they ate.
This reassuring result is similar to those of previous studies … which also have not found any adverse developmental effects from the low levels of mercury found in American and other mothers.
“This study shows no evidence of a correlation between low level mercury exposure and autism spectrum-like behaviors among children whose mothers ate, on average, up to 12 meals of fish each week during pregnancy,” said study lead author Edwin van Wijngaarden, Ph.D. (URMC 2013)
Principal investigator Philip Davidson, Ph.D., noted that the outcomes suggest it's safe for mothers to eat ample of amounts of seafood:
“This study shows no consistent association in children with mothers with mercury levels that were six to 10 times higher than those found in the U.S. and Europe. This is a sentinel population and if it does not exist here than it probably does not exist.” (URMC 2013)
Cindy Lawler, Ph.D., of the National Institutes of Health said the results support the safety of eating ocean fish during pregnancy: “Although more research is needed, this study does present some good news for parents.”
Selected fish are best avoided by children and expectant mothers
The only documented and plausible risks to children relate to aquatic creatures that have less selenium than mercury:
- Whales and seals
- Fresh water fish from lakes and rivers polluted by coal plants
- The few ocean fish that deliver more mercury than selenium (shark, swordfish, tilefish, and king mackerel) … which the FDA and EPA advise children and pregnant/nursing mothers to avoid.
The new analysis of data from the Seychelles study affirms the highly credible hypothesis that the high levels of selenium found in almost all ocean fish prevents any brain and nerve damage from ingesting the mercury in them.
- 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.
- University of Rochester Medical Center (URMC). Study: No Link Between Mercury Exposure and Autism-like Behaviors. July 23, 2013. Accessed at http://www.urmc.rochester.edu/news/story/index.cfm?id=3893
- Ralston NV. Selenium health benefit values as seafood safety criteria. Ecohealth. 2008 Dec;5(4):442-55. Epub 2009 Apr 14.