With Mercury and Pesticides, Is Fish Oil Safe?

Health Professional

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.

People are sometimes fearful of the blood-thinning effects of fish oil. Fish oil does indeed inhibit platelets (a blood-clotting cell) and reduce blood clotting factors like fibrinogen. However, bleeding problems from fish oil are exceptionally rare. I have never witnessed an adverse bleeding effect from fish oil in thousands of patients. Fish oil remains very safe even if taken with aspirin. In fact, the modest blood thinning effects of fish oil are desirable, since the majority of heart attacks and strokes are based on an increased tendency to form blood clots (on ruptured atherosclerotic plaques).

The only time there may be some concern over excessive blood thinning is if you take warfarin (CoumadinTM), a full-strength blood thinner, or if you have an abnormal bleeding tendency like sickle cell anemia or other clotting factor deficiency. In these instances, discuss the use of fish oil with your doctor. But in the huge majority, fish oil is safe and does not expose you to excessive risk of bleeding.

All in all, in my view, the benefits of fish oil far, far outweigh the risks─if any. The omega-3 fatty acids are a critical ingredient in any heart disease prevention program. Judging from the best information we have from unbiased sources, there is no reason to deprive ourselves of this wonderful health tool.