Fish and fish oils, which are high in the omega-3 polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are among the super foods whose known benefits continue to expand over decades of research.

Studies have documented protection against chronic inflammation, cardiovascular disease, depression, age-related macular degeneration, attention deficit disorder, cognitive decline, arthritis, and much more in association with fish and/or fish oil intake.

The extent of the research documenting the benefits of fish is so impressive as to have led one gerontologist to quip that “We ought to put fish in the water.” The predicament is consumers are concerned about consuming [enough] fish because of the potential for mercury contamination.

Mercury is a naturally occurring element that has no known benefit in the human body.

The element, which is present in the air due to natural and manmade causes, becomes methylmercury in water.

Larger fish that are higher on the food chain concentrate more methylmercury in their bodies than small fish.

Some of these fish, including swordfish, tilefish, shark, king mackerel and, to a lesser extent, white albacore tuna, have high methylmercury levels and pregnant women are advised to avoid consuming them due to an associated risk of brain damage, vision and hearing problems in their infants.

At one time, pregnant women were advised to limit the intake of other fish as well, but this is no longer the case.

Risk vs. Benefit Analysis

In 2002, the American Heart Association issued a Scientific Statement recommending the intake of omega-3 from fish and plants to help protect the heart.1 While plants such as soy and flax contain the omega-3 fatty acid alpha linoleic acid (ALA), this fatty acid has not been associated with as many benefits as EPA and DHA, which are found in fish or the algae they consume.

A review published in 2006 in the Journal of the American Medical Association evaluated the effects of fish or fish oil on cardiovascular risk, methylmercury and fish oil's effect on early neurodevelopment, mercury's risks in adults, and the health impact of dioxins and polychlorinated biphenyls (PCBs) contained in fish. Authors Dariush Mozaffarian, MD, DrPH, and E. B. Rimm, ScD, concluded that “For major health outcomes among adults, based on both the strength of the evidence and the potential magnitudes of effect, the benefits of fish intake exceed the potential risks. For women of childbearing age, benefits of modest fish intake, excepting a few selected species, also outweigh risks.”2

In 2008, research reported in the American Journal of Clinical Nutrition, scientists at Harvard and the Statens Serum Institut in Cophenhagen concluded that mothers who consumed more fish during pregnancy and breastfeeding actually had children who experienced improved development in comparison with children whose mothers consumed less.3

Seven years later, the journal published a study of Seychelles Islanders, where the larger fish intakes result in methylmercury exposures that are ten times higher as compared to people in the U.S.4 “These findings show no overall association between prenatal exposure to mercury through fish consumption and neurodevelopmental outcomes,” reported study coauthor Edwin van Wijngaarden, PhD, of the University of Rochester Department of Public Health Sciences. “It is also becoming increasingly clear that the benefits of fish consumption may outweigh, or even mask, any potentially adverse effects of mercury.”

Interestingly, a study of rats exposed to methylmercury found that supplementation with fish oil  protected DNA from damage that normally results from mercury exposure.

The authors of the study suggest this benefit is due to fish oil’s ability to reduce inflammation.5

An investigation of five brands of fish oil conducted by researchers at Massachusetts General Hospital and Harvard Medical School found levels of mercury that ranged from negligible to nondetectable.6 Authors S. E. Foran and colleagues noted that the mercury content of fish oils was similar to that which normally occurs in human blood. They suggest that consuming fish oils may be safer than eating fish.

Recent advancements in fish oil production have made the likeliness of any significant presence of mercury even lower than indicated by studies such as these. An effort is made by fish oil suppliers to obtain fish from areas of the ocean that have low contaminant levels. High quality fish oil is distilled, extracted and redistilled which ensures removal of any potential contaminants and a higher concentration of EPA and DHA.

The Bottom Line

While it’s still a good idea to avoid eating swordfish, tilefish, shark and king mackerel, there’s no reason to be concerned about mercury in fish oil if purchased from a reliable supplier. Look for a fish oil that has a Five-Star International Fish Oil Standards (IFOS™) rating to ensure top quality and safety.

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