Mercury Toxicity: Do You Need To Worry About Eating Fish?

Mercury Toxicity Do You Need To Worry About Eating Fish
Mercury Toxicity Do You Need To Worry About Eating Fish

There’s no shortage of fear-mongering around the evils of mercury. We hear about its use in vaccines and dental amalgams but where we hear it the most is in any discussion about eating fish. To be clear, I’m referring to methyl-mercury not ethyl-mercury; there is a difference and they are metabolized differently.

The focus of this post is to see whether or not there are any grounds for the broad stroke recommendation for everyone to minimize how much fish and seafood they eat in the name of reducing mercury exposure and whether there’s a downside of such generalized advice?


Governmental Advice On Fish Consumption

Health Canada, like most health branches of governments, recognize the many health benefits of omega-3 fats which is why they recommend 2 servings of fish per week. The bulk of the evidence shows that getting more omega-3 fats improves overall health, there’s no denying this but there’s also a general sense of concern among the public about eating fish and seafood due to mercury content.

Apart fromHealth Canada, other agencies around the globe, including the EPA and FDA in the US, has also issued recommendations on fish and seafood consumption as it relates to mercury. In 2008, Health Canada updated its 2002 dietary advice about mercury in fish. In a nutshell, they suggest that most Canadians shouldn’t be concerned about the amount of mercury in fish and that most of the species of fish that are consumed in Canada have low levels of mercury.


They do state that there are a few species that have unacceptable amounts and should, therefore, be avoided or at least their consumption very restricted. These include:

o fresh/frozen tuna
o shark
o swordfish
o marlin
o orange roughy
o escolar
o tilefish


Because canned albacore tuna is higher in mercury than canned light/skipjack/tongol/yellowfin tuna, Health Canada cautions that there is a potential for exposure to higher levels of mercury and, therefore, puts limits for specific groups; children and women who are, or may become, pregnant or are breastfeeding. They recommend limiting albacore tuna to 75 g or 2.5 ounces, or 125 ml or 1/2 cup which is equal to about 1/2 a 170 g can, per week.

While these recommendations were and still are intended for women during pregnancy, breastfeeding women and children, they’ve been erroneously extrapolated to all members of the public. The general word on the street when it comes to eating fish and seafood when it comes to mercury? —Proceed with extreme caution.


Is The Concern About The Mercury In Fish Exaggerated?

As stated above, people don’t need to worry about the trace amounts of mercury in the vast majority of fish Canadians eat; the levels just aren’t high enough to pose a health risk. But regardless, to only hear about the mercury content of fish means the public is only getting half the story which is that selenium plays a huge role in preventing mercury toxicity and the GOOD NEWS is that many of the fish that people routinely eat are high in selenium. The SAD NEWS is that this fact has been known about for decades with some of the earliest research as far back as the late 1960s yet the public remains unaware.

Selenium Protects Against Mercury Toxicity

Mercury loves selenium, so much so, that it preferentially binds to it interfering with selenium’s well-known role as the critical mineral in an enzymatic antioxidant. So long as there’s plenty of selenium in one’s diet, mercury toxicity is prevented in one of two ways:


1] There’s enough selenium to bind to mercury to sequester it

2] the extra selenium maintains the antioxidant glutathione peroxidase whose job it is to protect vital tissues from oxidation and inflammation, not the least of which is the brain.


Dietary and tissue selenium in relation to methylmercury toxicity

Studies that have found negative health effects of mercury-containing fish were those species that were also low in selenium. With depleted bodily selenium stores, methyl-mercury is indeed potentially toxic. Simply looking at the mercury content of any given fish misses the mark – big time – when it comes to advising people on fish consumption. This is evident in the guidelines put out by most governments which, in turn, influences the advice from doctors and nutrition professionals. This misinformed viewpoint is further distorted in the media.


Fortunately, most of the fish found in the food supply have a lot more protective selenium than mercury as evidenced in the diagram below.

Mercury Toxicity Do You Need To Worry About Eating Fish
Mercury Toxicity Do You Need To Worry About Eating Fish

The benefits of eating fish far outweigh any theoretical risks.

The bulk of the evidence is clear: regular fish consumption, [ideally from sustainable stocks], benefits overall health.

Fish Intake, Contaminants, and Human Health. Evaluating the Risks and the Benefits

This is still true for pregnant women and their developing child. One study found that women who ate more seafood did have higher levels of mercury in their umbilical cord blood, but that did not result in poorer health in children, in fact quite the opposite, the children of the fish and seafood eaters had better motor development and higher verbal and total IQ.

Relation between Cord Blood Mercury Levels and Early Development in A World Trade Center Cohort

This study is consistent with other studies that looked at omega-3 fats & fish consumption and fetal and child development.

Bottom line

Advising pregnant women, children and adults of any age to reduce their fish consumption as a way to avoid mercury is ill-informed. In fact, pregnant women should be eating more oily fish than most currently are. While it’s true that some species of fish such as swordfish, shark, tilefish, marlin and others already mentioned, should be limited because they lack selenium, the vast majority of fish are safe to eat by all groups of people.

As a general rule, if a fish species contains more selenium than mercury, it’s safe to eat. You can also protect yourself from mercury but ensuring you include other selenium-rich foods in your diet.

On a completely different side note, I was curious to know what my blood mercury level was so my doctor tested it. I occasionally eat sashimi but do eat canned salmon about twice a month, and canned skipjack tuna about 6 or 7 times a month. My mercury was 5.8 nmol and according to the lab reference range, it should be less than 18 nmol.

My MD said he has seen 80-100 nmol in those who eat a lot of sushi and sashimi [higher mercury containing fish] (several times a week). Those consuming high mercury-containing fish almost daily can have levels as high as 998 nmol/L, with 500 nmol/L being the cut off for acute toxicity.

To learn more about which fish stocks are a better choice with respect to the environment and sustainability, check out Sea Choice for more information.