Should you still eat fish even if there’s a chance you could get mercury poisoning?

DEAR DOCTOR K:

I’ve been hearing for years that eating fish is healthy. But I also hear that mercury and other poisons can be in fish. I like the taste of fish, but should I seek it or avoid it?

DEAR READER:

Questions from readers so often ask about the benefits versus the risks of lifestyle practices, or medical tests and treatments. That’s because most things have both benefits and risks — and eating fish is no exception.

Fish ranks way up there on the list of healthful foods we should be eating. It’s an excellent source of protein, and its healthy oils protect against cardiovascular disease. A diet rich in seafood benefits the brain and the heart.

But depending on the species and the water it was harvested from, fish comes with a catch. Nearly all fish and shellfish do contain traces of mercury, and mercury is a toxic metal. If too much gets into your body, it can be damaging — particularly to the brain.

As small fish are eaten by larger fish up the food chain, concentrations of mercury increase. Thus large, predatory, deep-ocean fish tend to contain the highest levels. Examples include shark, swordfish, tilefish and king mackerel.

Please don’t misunderstand me: I’m not saying it’s unhealthy to eat a meal of these fish — I had a swordfish dinner just last week. But I’m careful about how often I eat these fish, in contrast to those with less mercury.

Most adults can safely eat about 12 ounces (two 6-ounce servings) of a variety of cooked seafood a week. This advice does not include the large, predatory ocean fish mentioned above, which should be enjoyed only occasionally. Also, pay attention to local seafood advisories about contamination.

Both the benefits and risks of eating fish may be higher in women who are pregnant or may become pregnant, nursing mothers and children ages 12 and younger. It is a paradox. On one hand, babies in the womb and young children with growing brains benefit from the omega-3 fatty acids in fish. On the other hand, mercury and other toxins probably have greater negative effects in those same growing brains.

For such women and children, 12 ounces a week of fish is considered safe if they:

  • Generally choose fish and shellfish that are lower in mercury, like shrimp, canned light tuna, salmon, pollock and catfish.
  • Eat no more than 6 ounces (one average meal) of albacore (white) tuna per week, because it has more mercury than canned light tuna.

Fish oil supplements, of course, contain the “good” omega-3 fatty acids but generally no mercury. (Caveat: Check with a reliable source such as Consumers Union about testing of fish oil supplements for mercury. The Food and Drug Administration does not check the quality with which supplements are manufactured.) So, fish oil supplements theoretically might be a good idea for pregnant women and young children. However, I’m not aware of any solid evidence that pregnant women or young children benefit from such supplements.

(This column is an update of one that ran originally in March 2012.)