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One in 12 U.S. women of childbearing age have potentially hazardous levels of mercury in their blood as a result of consuming fish, according to government scientists.

The findings support previous recommendations that pregnant women limit their dietary intake of fish, as it is a leading source of mercury in people, and a fetus is highly vulnerable to mercury toxicity.

The U.S. Food and Drug Administration (FDA) recommends that pregnant women and those who may become pregnant avoid eating shark, swordfish, king mackerel, and tile fish known to contain elevated levels of methylmercury, an organic form of mercury.

Mercury exposure can also cause permanent damage to the brain and kidneys.

Nearly all fish contain some amount of methylmercury. Mercury accumulates in the system, so larger, longer-lived fish like shark or swordfish contain the highest amounts of mercury and pose the largest threat if eaten regularly.

Researchers assessed fish consumption and measured levels of mercury in the blood of 1,709 women between the ages of 16 and 49 years and 705 children between the ages of one and five years.

The U.S. Environmental Protection Agency’s recommended reference dose, or level below which exposures are considered harmless, of mercury in the blood is 5.8 micrograms per liter. The average level of mercury in the women's blood was about one microgram per liter, well below the reference dose.

However, about eight percent of the women had levels that above the reference dose. Further, women who ate at least three servings of fish during the 30 days prior to the study had mercury levels of close to two micrograms per liter--four times higher than those of women who did not eat fish.

Adult women had three times higher blood mercury levels than children, partly because adults tend to eat more fish than children, according to researchers.

Researchers noted that fish can be nutritious and that the American Heart Association recommends people eat two servings of fish per week.

Fish such as haddock, tilapia, salmon, cod, pollock and sole, as well as most shellfish tend to be relatively low in methylmercury, according to researchers.

Journal of the American Medical Association 

April 2, 2003;289:1667-1674

This is astounding news that requires us all to re-think our attachment to the idea that fish is a healthy food for humans.  This belief was true many decades ago when the oceans were not so polluted.  Unfortunately the contamination of fish with mercury, DDT/DDE by products and other heavy metals and toxins make wild fish a lot less appealing as a source of omega-3 fatty acids.  Some safer fishes are listed below.

Of course, despite the facts of this above article, it is NOT recommended to have mercury amalgam fillings put into cavities and I do recommend those of you who have mercury amalgam fillings to have them replaced soon or later, depending on your own mercury toxic load.  I've seem many patients who have very elevated mercury levels due to a diet high in fish and shellfish with the idea that these foods are health foods.  Increasingly now restaurants are purchasing farmed fish due to the lower cost (and greater profit for them) and serving them to their customers.  These fish are not fed their natural diet and are their color is derived from artificial coloring agents to make them seem appealing to consumers.  Also their beneficial omega-3 levels are significantly reduced due to their un-natural diet.  

A hair analysis for toxic elements will identify your own recent (past 3 months) exposure to mercury, arsenic, lead and many other toxic heavy metals.  The more consumed mercury, the higher levels of mercury in your hair.  Call our office for a test kit and instructions on how to do the test.  As always, I hope that in the future the oceans can recover from the toxic pollution that is so harmful to us and our aquatic friends.  Until then choose other sources of omega-3 rich foods such as grass fed beef, ostrich, grass fed bison or buffalo, amaranth greens, ground flax seeds (not flax oil), and some of the above fish.

Dr. Suzann Wang