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Dangers of Fish Oil Supplements

By Clay McNight

Although fish oil supplements are touted for their health benefits, related to their rich concentration of omega-3 fatty acids, many people wonder if those benefits are being canceled out by dangerous contaminants, most notably mercury and PCBs, making their way into the supplements.


Mercury is a heavy metal that exists in various forms. According to the Environmental Protection Agency (EPA), the most common way Americans are exposed to mercury is through consuming fish containing a form of mercury known as methylmercury. For babies, fetuses and children the most noted health consequence associated with methylmercury exposure is diminished brain development. Other health effects can include a lack of muscle coordination, impaired speech and hearing, muscle weakness and impaired peripheral vision. Fish high in mercury include shark, swordfish, tilefish and king mackerel and fish lower in mercury include shrimp, tuna, catfish, salmon and pollock.


PCBs or Polychlorinated Biphenyl are a class of organic, man-made chemicals that were manufactured in the past for a variety of commercial uses including plastics, caulking, floor finishes, carbonless copy paper, transformers, capacitors and cable insulation. PCBs were banned in 1979 but they still exist in the environment today. According to the EPA, these chemicals break down slowly and can be carried long distances, cycling between air, water and soil. PCBs are known to cause cancer, as well as other negative health effects on the reproductive system, immune system and nervous system. PCBs can accumulate in the bodies of small fish, which puts those who consume fish at risk for PCB contamination.

Fish Oil Tests

In 2012, Consumer Lab tested a variety of fish oils for mercury and PCBs. The tests revealed only trace levels of PCBs in most brands and none of the brands were found to contain mercury. According to Consumer Lab, a serving of fish meat is more likely to be contaminated than a fish oil supplement. A 2009 study published in "Nuero Endocrinology Letters" also tested fish oil capsules and cod liver oil for mercury and PCBs. The test revealed that all samples were below the detection limit for mercury and some PCBs were found in low concentrations. The study concluded that fish oil capsules and cod liver oil are safe and healthy.

Drug Interactions and Side Effects

Medline Plus notes that fish oil supplements are "likely safe" as long as they are consumed in doses of 3 grams or less per day. Higher doses may reduce immune activity and slow blood clotting, which increases the risk of bleeding. Fish oil supplements can also lower vitamin E levels. Side effects can including fishy burps, rash, nosebleeds, heartburn, nausea and loose stools. If you have any health conditions, particularly liver disease, seafood allergies, bipolar disorder, depression, diabetes, high blood pressure or HIV/AIDS, do not use fish oil unless you are under the supervision of a healthcare professional. Fish oil may react with some medications, including drugs for high blood pressure, contraceptive drugs, orlistat and medications that slow blood clotting.

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