Fish has given fish oil a bad name.

Because questions have been raised over mercury and pesticide residues in fish when eaten, some people have been reluctant to add fish oil supplements to their health regimen.

But they shouldn't be.   

There is no question that some types of fish, particularly large predatory fish like swordifish, shark, and king mackerel, contain higher quantities of methylmercury, the absorbable form of mercury that, if sufficient exposure develops, results in nervous system damage and increased heart attack risk.

(The U.S. Environmental Protection Agency (EPA) and the FDA  provide some guidance on mercury and pesticide content of fish: Draft Summary of Published Research
Section A - Cardiovascular Disease at http://www.cfsan.fda.gov/~dms/mehgova.html.)

This leads to the logical question of whether fish oil from fish might also pose risk for mercury and pesticide exposure.

Are there mercury and pesticides in fish oil?

First of all, most fish oil is not obtained from large carnivorous fish, but from menhaden, salmon, and sardines, lower down on the food chain and not themselves exposed to much mercury. The low mercury and pesticide content of these types of fish have been verified in several analyses.

Nonetheless, do some mercury and pesticide residues make their way to our fish oil capsules?

We turn to several sources of information outside of the fish and fish oil industry:

A 2003 Consumer Reports test of 16 different off-the-shelf brands of fish oil revealed virtually no mercury, dioxin, or polychlorinated biphenyls (PCBs) in any of the tested samples.

A testing survey conducted by Consumer Labs (www.consumerlab.com) of 41 different brands passed 39 brands, including Carlson, Coromega, and Puritan's Pride; one brand failed because it contained less than the stated quantity of EPA, and another failed because it was spoiled. None failed because of increased levels of mercury, dioxin, or PCB's.

Consumer Labs recently expanded their analysis to a total of 59 brands; all preparations passed except one because of faster-than-expected dissolution of an enteric-coated capsule, but not for mercury or pesticide contamination. The required levels for passing included a strict mercury content of < 0.1 part-per-million (ppm) of mercury, with similar strict criteria for polychlorinated biphenyls (PCBs) and dioxin.  

Though not perfect, that's a darn good track record. This doesn't prove, of course, that every brand among the hundreds available are reliable and safe, but it's a pretty good indication that, if you purchase from a reputable source, you're likely to get high-quality fish oil free of dangerous contaminants.

What are the other unwanted effects of fish oil?

The most common is fishy belching-harmless though annoying. Minimize this effect by shopping around for different preparations. (They can vary dramatically in this effect.) Costco and Sam's Club both carry excellent preparations that cause minimal fishy belching; both also sell enteric-coated versions that delay dissolution past the stomach and thereby reduce fishy belching. You might search for some new liquid fish oil preparations (non-encapsulated; we've had good results with Carlson's lemon flavored preparation) that tend to be high quality and therefore less fishy.