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Nora Saul, MS, RD, LDN, CDE

Manager, Nutrition Services
Joslin Diabetes Center
Boston, MA

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Mercury and Fish Oil Supplements

Ask the Expert


I take a daily supplement of Omega-3 fish oil. I recently saw an advertisement for "mercury free" fish oil. Mine does not say mercury free. Are most supplements mercury free or is this something I should search for?


The oils found in cold-water fatty fish are prized for their beneficial effects on the heart and circulatory systems. Research indicates that marine-derived omega-3 fatty acids have the ability to reduce cardiac arrhythmias and triglyceride levels and decrease the risk of cells sticking together and forming a clot. Experts recommend the general public consume between .3 to .5 grams per day of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). This means you should eat two servings of fatty fish per week.

If you do not like fish or cannot eat it or you have a need for higher levels of omega-3s to treat a specific condition, fish oil capsules are a practical alternative. In addition, as our oceans become more and more polluted with the byproducts of our industry, heavy metal contamination of marine life is a real threat to certain populations, such as children and pregnant women.

Fish oil supplements do not appear to have the same contamination problems as fish. A study in the January 2005 issue of the Archives of Pathology and Laboratory Medicine found that fish oil supplements contained very few contaminants. That study tested the brands Omega Brite, Nordic Ultimate, Sundown, Kirkland and CVS. has also tested a variety of fish oil supplements and found that they met safe levels for mercury and PCS.

Most fish oil in supplements has been purified using methods such as molecular distillation to ensure that the oil products do not contain significant levels of environmental toxins. When buying a supplement, look for a product's verification that it meets the environmental protection agency's (EPA's) allowable limits for contaminants.

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