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Mercury in Seafood

Health professionals and researchers know that seafood is good for your health and encourage a diet high in these important foods. However, at the same time, government agencies have issued advisories urging caution about eating certain species of seafood from specific waters. Understandably, this can cause confusion or misperceptions about these food sources, as this mixed message distorts the real risks while concealing the many benefits of a diet high in seafood.

Selenium: Mercury Neutralizer

The best science indicates that trace amounts of mercury in the fish Americans eat simply aren't high enough to pose a health risk. But measuring only mercury further exaggerates this hypothetical risk. There's another scientific wrinkle that few environmental groups are talking about – largely because it doesn't help to promote their scare campaigns. An accurate picture of the health consequences of eating fish must include other substances that affect the way mercury interacts with the human body.

Selenium is plentiful in fish, but the public hasn't heard much about its role in the mercury puzzle. As biochemists, pharmacologists, and neurologists study this nutrient, we're gaining a better understanding of its importance.

In scientific jargon, selenium has an unusually high "binding affinity" for mercury. In layman's terms, this means that when the two elements are found together, they tend to connect, forming a new substance. This makes it difficult for the human body to absorb the mercury separately. So when mercury "binds" to selenium, it's no longer free to "bind" to anything else – like brain tissue.

The research world is still developing explanations for exactly how selenium cancels out mercury's potentially toxic effects, but most scientists accept one of two competing theories.

The conventional idea describes selenium as a sort of "mercury magnet." Under this theory, once selenium is digested it can locate and neutralize mercury molecules. In one study, Japanese researchers found that adding selenium to the diets of birds "gave complete protection" from large amounts of mercury. Research carried out by scientists in Scotland and the Philippines has concluded that the relationship between mercury and selenium is one of "toxicological antagonism." And in the United States, the Environmental Protection Agency describes selenium as an element that is "antagonistic to the toxic effects of mercury."

The more recent selenium hypothesis holds that mercury takes a more active role in the relationship. Under this theory, when mercury enters the body it seeks out selenium and takes it out of circulation, preventing the body from creating enzymes that depend on selenium to perform their functions. Enzymes are special proteins that control the various steps in chemical reactions that make life possible. Without enough selenium-based enzymes, the functions of the brain and other organs can be affected.

While this might sound scary, problems can only occur if we don't get enough selenium to counteract the trace amounts of mercury in the fish we eat. And fish are so rich in selenium that this is not likely to happen. The U.S. Department of Agriculture has measured selenium levels in more than 1,000 commonly consumed foods, and 16 of the 25 best sources of dietary selenium are ocean fish. University of North Dakota environmental scientist Dr. Nicholas Ralston is an expert on the relationship between selenium and mercury. Here's how he describes it:

Think of dietary selenium as if it were your income and dietary mercury as if it were a bill that you need to pay. Just as we all need a certain amount of money to cover living expenses such as food and rent, we all need a certain amount of selenium ... Only one major study has shown negative effects from exposure to mercury from seafood, and that seafood was pilot whale meat. Pilot whale meat is unusual in that it contains more mercury than selenium. When you eat pilot whale meat, it's like getting a bill for $400 and a check for less than $100. If that happens too much, you go bankrupt. On the other hand, if you eat ocean fish, it's like getting a check in the mail for $500 and getting a bill for $25. The more that happens, the happier you are.

Dr. Ralston is right. Researchers at the National Oceanic and Atmospheric Administration found that most of the fish we eat contains significantly more selenium than mercury. Seafood that contains more mercury (Hg) than selenium (Se) includes pilot whale, tarpon, marlin, and some shark. Fish we most commonly consume, including all forms of tuna and swordfish, are rich in selenium.

Selenium Relative to Mercury

On the other end of the scale, pilot whale is by far the worst offender. This may help explain why researchers in the Faroe Islands insist that dietary mercury is harmful to island residents. (Unlike the vast majority of people, the Faroese eat lots of pilot whale meat.) By contrast, a similar study in the Seychelles Islands – where people eat lots of selenium-rich fish but no whale meat – found no negative health effects from the tiny amounts of mercury in fish.

Mercury levels not increasing

One popular myth is that the amount of mercury in our environment (and in the fish we eat) is dangerously increasing. However, the truth is that there is considerable evidence that the amount of mercury in fish has remained the same (or even decreased) during the past 100 years.

One team of researchers from Duke University and the Los Angeles County Natural History Museum compared 21 specimens of Atlantic Ocean blue hake preserved during the 1880s with 66 similar fish caught in the 1970s. They found no change at all in the concentration of mercury.

In another study, Princeton scientists compared samples of yellowfin tuna from 1971 with samples caught in 1998. They expected to find a mercury increase of between 9 and 26 percent, but they found a small decline instead.

And in a unique experiment, curators of the Smithsonian Institution tested tuna samples that were archived between 1878 and 1909, and compared them with similar fish tissue from 1971 and 1993. They found significantly less mercury in the more recently caught fish. In some cases, the difference was more than 50 percent.

There's even some evidence that human beings are exposed to less mercury today than in the past. Alaska's Public Health Department, for example, reports that when the hair of eight 550-year-old Alaskan mummies was tested for mercury, the results showed levels averaging twice the blood-mercury concentration of today's Alaskans.

Trace amounts

Another popular myth is that mercury in fish presents a serious health risk to Americans. Actually, the truth is that the best science suggests that the tiny amounts of mercury in fish aren't harmful at all.

A recent twelve-year study conducted in the Seychelles Islands (in the Indian Ocean) found no negative health effects from dietary exposure to mercury through heavy fish consumption. On average, people in the Seychelles Islands eat between 12 and 14 fish meals every week, and the mercury levels measured from the island natives are approximately ten times higher than those measured in the United States. Yet none of the studied Seychelles natives suffered any ill effects from mercury in fish, and they received the significant health benefits of fish consumption.

In November 2005, The American Journal of Preventive Medicine published new research from Harvard University that put the risk from fish-borne mercury in its proper context. Dr. Joshua Cohen, the study's lead author, summed up the issue for MedScape Medical News: "[W]e're talking about a very subtle effect of mercury … changes that would be too small to measure in individuals."

Benefits outweigh the risk

Finally, consumers are falsely led to believe that the health risk from mercury outweighs the health benefits of eating fish. On the contrary, the opposite is true.

Omega-3 fatty acids found in fish can decrease the risk of heart attacks, strokes, kidney disorders, Alzheimer's disease, breast cancer, prostate cancer, uterine cancer, rheumatoid arthritis, type-2 diabetes, low birth-weight, post-partum depression, and pre-term delivery. Partially because of the health scares surrounding mercury, Americans' intake of Omega-3 acids is 3 to 6 times lower than the levels recommended by the National Institutes of Health and the American Heart Association.

Harvard's Dr. Eric Rimm told The New York Times in 2004: "The message of fish being good has been lost, and people are learning more about the hypothetical scare of a contaminant than they are of the well-documented benefits."

A 2005 study published in Archives of Neurology showed that elderly people who eat fish at least once a week can slow their rate of mental decline by between 10 and 13 percent. Research published in the same journal in 2003 found that adults who consume fish once or more each week have a 60 percent lower risk of developing Alzheimer's disease. A 2004 study of children in Bristol, England showed that the children of pregnant women who consumed high amounts of fish scored higher on mental development tests. That same study found "no adverse developmental effects associated with mercury."

And studies published in the November 2005 American Journal of Preventive Medicine found that even eating small amounts of fish each week can result in a 17 percent lower risk of heart disease, a 12 percent lower risk of stroke, and (when eaten by pregnant women) a modest 1 to 8-point increase in children's IQ.


mercuryfacts.org The Center for Consumer Freedom has created an informative website to help navigate the confusion surrounding the truth about mercury in seafood. They have a detailed website called mercuryfacts.org that can be visited by clicking here.  To read their fact sheet entitled “10 Essential Mercury Facts”, click here.


Source: Center for Consumer Freedom

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