from MedScape
(Skip to "Studies of five fish oil supplements" near the end of this for the specific information about toxins in some common fish oil supplements)
Jan. 28, 2005 Fish oil supplements may be safer than eating fish, at least from the standpoint of toxic impurities, according to the results of a study published in the January issue of the Archives of Pathology and Laboratory Medicine.
"The consumption of fish high in omega-3 fatty acids is advocated by the American Heart Association to decrease the risk of coronary artery disease," write Stacy Foran Melanson, MD, PhD, from the Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts, and colleagues. "However, fish contain environmental toxins such as mercury, polychlorinated biphenyls, and organochlorine [OC] pesticides, which may negate the beneficial cardiovascular effects of fish meals."
OC analysis of the contents of five commercial fish oil brands revealed that the levels of polychlorinated biphenyls (PCBs) and OCs were all below the detectable limit.
"Fish oil supplements are more healthful than the consumption of fish high in organochlorines," the authors write. "Fish oils provide the benefits of omega-3 fatty acids without the risk of toxicity. In addition, fish oil supplements have been helpful in a variety of diseases, including bipolar disorder and depression."
The authors note that of the PCBs produced in the U.S. before 1976, 1.2 billion pounds entered rivers, lakes, and oceans, where they accumulate in bottom-feeding fish and become more concentrated higher up on the food chain (0.6-20 parts per million [ppm] in edible fish high in the food chain). In 1984, the Food and Drug Administration (FDA) lowered the limit to 2.0 ppm for edible fish.
Similarly, OC pesticides entered the air, water, and soil when they were sprayed on crops and forests and concentrate more than 1,000-fold in fish and marine mammals. These pesticides, including DDT, were banned in 1973 because of their neurotoxic properties.
Although consumption of 200 to 400 g of oily fish each week has been recommended to protect against cardiovascular disease, regular fish intake presents potential problems, particularly in children and pregnant women.
The authors estimate that compared with fish oil supplementation, regular consumption of fish from the Great Lakes would expose humans to at least 70 times more PCBs and 120 times more OC pesticides.
"Our data concerning the levels of OCs suggest that fish oil supplements may be preferable to fish consumption as a dietary guideline for the general population and as a therapeutic source of omega-3 fatty acids in patients with cardiovascular disease and depression," the authors conclude.
The authors report no relevant financial interests.
Arch Pathol Lab Med. 2005;129:74-77
Clinical Context
Consumption of 200 to 400 g per day of fish high in omega-3 polyunsaturated fatty acids is advocated by the American Heart Association to decrease coronary heart disease risk, according to the authors. Other potential benefits of omega-3 fatty acids listed by the authors based on previous studies include mood stabilization in bipolar disorder, depression in pregnancy, and reduced inflammation in some autoimmune diseases, such as rheumatoid arthritis. However, certain fish contain high levels of toxins such as mercury, PCBs, OC pesticides, and related compounds that may negate the health advantages of fish meals. Recent concern has been raised about the levels of toxins in both wild and farm-raised fish. The U.S. FDA allows 0.10 to 3.0 ppm of PCBs in all foods, but in 1984 lowered the limit for fish to below 2.0 ppm. Consumption by children and pregnant women are of particular concern. The authors had previously shown that fish oil supplements contained negligible amounts of mercury and thus may be a safe substitute to fish for omega-3 fatty acid intake.
This is a review of the potential risks and benefits of fish and fish oil consumption, and a report on the concentration of PCB and OC found in five brands of fish oil supplements.
Study Highlights
Review of toxins
-PCBs are colorless and odorless chemicals widely used in electrical equipment such as transformers before 1977. 1.2 billion pounds of PCBs in the U.S. ended up in rivers and oceans before 1977 and were concentrated from bottom fish to edible fish higher in the food chain.
-OCs were used as pesticides and sprayed on crops and forests, entering the air, water, and soil. They were deposited in sediment and still taken up by small fish and organisms today due to their resistance to degradation.
-Both PCBs and OCs are present in the environment. Humans have on average 1.4 parts per billion (ppb) of PCBs in their serum. Levels are higher in fatty tissue and breast milk.
-PCBs and OCs are stable and nonflammable as industrial agents with half-lives as long as 5 years. OC pesticides concentrate 1,000-fold in fish and marine mammals. In the 1990s, DDT and its metabolites were detected in 94% of whole fish samples.
-PCBs and related compounds accumulate in adipose tissue and are metabolized in the liver. Adverse effects include reproductive, dermatologic, developmental, endocrine, hepatic, and immunologic.
-Acute exposure to OCs, the best known of which is DDT, can cause neurotoxicity including tremors, seizures, headaches, vomiting, and dizziness. Chronic exposure is associated with reproductive, neurologic, hepatic, and carcinogenic effects. DDT has been shown to be a human carcinogen.
-Developmental defects and lower IQ are associated with in utero exposure to both classes of agents.
-Cold water fish (eg, as measured in fish from the Great Lakes and the Baltic Sea) contain high levels of PCBs, OC pesticides, and mercury. PCB and OC levels increase with age of the fish.
-Farm-raised salmon have significantly higher levels of PCB, fat, and cholesterol than wild salmon and can lead to higher PCB intake than the allowable level.
-Mercury is found in equal concentrations in wild and farm-raised fish.
-In one study, anchovy, mackerel, cod, and red mullet showed highest levels of PCB and OC content. Calamari, cob-fish, and mussels had intermediate levels and sole, cuttle, frog-fish, scampi, and hen clam had the lowest concentrations.
-Small but detectable levels of PCBs and OCs have been found in fish oil supplements in European studies.
Studies of five fish oil supplements
-5 over-the-counter (OTC) brands of fish oil capsules (Omega Brite, Kirkland, Natrol Sundown, and CVS) were punctured, and 5 mL of liquid content from each capsule sent in a citrate tube to National Medical Services for analysis.
-PCB and OC levels were measured by gas chromatography with electron capture. Lower limits of detection were 400 ppb for PCB and 200 ppb for OC.
-None of the 5 brands contained detectable amounts of PCBs or OCs.
-Previously, the authors reported nonsignificant amounts (less than 12 g/L) of mercury in 5 brands of fish oil: Omega Brite, Nordic Ultimate, Sundown, Kirkland, and CVS.
Pearls for Practice
-Fish oil contains at least five times less PCB and 25 times less DDT than the FDA daily recommended limits and less OC than fish high in the food chain.
-Consumption of fish oil supplements vs fish meals may confer the benefits of omega-3 fatty acids without the risks of toxins.
