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:
- Shark
- Swordfish
- King Mackerel
- Tilefish
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.