Women who are pregnant should avoid eating canned tuna; it may contain high levels of methyl mercury, which may harm the developing nervous system of unborn babies and young children.
Although most canned light tuna contains an average of 0.12 parts per million (ppm) of mercury -- and is touted as a safer, lower mercury seafood choice -- 6 percent of cans tested contained more than 0.35 ppm, and as much as 0.85 ppm. White or albacore canned tuna had an average of 0.35 ppm.
Because methyl mercury builds up in fish as they get older (and bigger), larger, older fish, such as albacore tuna, tend to have higher mercury levels than smaller, younger fish.
The Food and Drug Administration advises that, due to high mercury levels, pregnant women should never eat:
- King Mackerel
According to Consumer Reports, king mackerel contains an average of 0.73 ppm of mercury -- which is lower than some cans of tuna.
The FDA's current recommendations for pregnant women, women who may become pregnant and children is to eat no more than 12 ounces, or two meals, of canned tuna (one of which may be white or albacore tuna) each week. They have not made public warnings about the potentially high mercury levels in some canned tuna because they believe the levels, when consumed as a single serving, do not pose a significant threat.
Eating clean healthy fish during pregnancy is an outstanding idea, as animal-based omega-3 fats are necessary for the complete development of the human brain during pregnancy and the first two years of life.
Omega-3 fat , especially DHA (docosahexaenoic acid), is so essential to a child's development that if a mother and infant are deficient in it, the child's nervous system and immune system may never fully develop, and it can cause a lifetime of unexplained emotional, learning, and immune system disorders.
Deficiencies of omega-3 fats have also been associated with premature deliveries.
The problem arises when women consume fish that are contaminated with mercury, which can cause as much brain damage as omega-3 can cause brain benefits.
An alarming 40 tons of mercury are released into the <st1:place w:st="on"><st1:country-region w:st="on">United States</st1:country-region> alone every year due to burning coal to generate electricity. Mercury pollution from coal-fired power plants moves through the air, is deposited in water and finds its way into fish, accumulating especially in fish that are higher up the food chain.
Fish like tuna, sea bass, marlin and halibut show some of the worst contamination, but dozens of species and thousands of water bodies have been seriously polluted.
As a result, women who eat a lot of fish during pregnancy, or even as little as a single serving of a highly contaminated fish, can expose their developing child to excessive levels of mercury. The toxic metal can cross the placenta to harm the rapidly developing nervous system, including the brain.
Some fish are especially problematic so you will want to avoid these fish just as you would alcohol if you are pregnant:
You can review the comprehensive report I posted a few years ago for other fish recommendations.
Personally, I rarely eat fish. When I do, it is almost always at home and is Vital Choice Alaskan salmon, which I have had tested on numerous occasions and contains less than .1ppm mercury. But my primary source of omega-3 fats are supplements like krill oil or fish oil.