DEAR DOCTOR K:

I enjoy eating fish, and I know that doing so can keep me healthier. But how worried should I be about mercury and other pollutants in fish?

DEAR READER:

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. In other words, like a lot of things in life, fish is a mixed blessing. You get some bad with the good, but you can minimize the bad and maximize the good. Here's how.

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 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.

In my judgment, this advice does not apply to women who are pregnant or may become pregnant, nursing mothers and children ages 12 and younger. That's because more caution is needed to avoid potential harm from mercury to a fetus's or a young child's developing nervous system. 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.

-- Albacore ("white") tuna has more mercury than canned light tuna. Eat no more than 6 ounces (one average meal) of albacore tuna per week.

Follow these recommendations when feeding fish and shellfish to your young child, but even so, you may want to serve smaller portions.

And it may be that a few sips of tea or coffee with your fish could lower the likelihood that any mercury you consume will harm you. Canadian researchers have shown that the combined effect of eating cooked fish and drinking tea or black coffee makes your body far less likely to take in mercury. It's an intriguing idea. But before I believe it, I'd need to see other studies that come to the same conclusion.

To sum up, if you're smart about how you eat fish, the good effects on your health far outweigh the bad.

(Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.)

** ** **

COPYRIGHT 2012 THE PRESIDENT AND FELLOWS OF HARVARD COLLEGE

DISTRIBUTED BY UNIVERSAL UCLICK FOR UFS