Fish contains high amounts of healthy lipids and proteins without the fat found in other meats. Unfortunately, studies indicate that the mercury found in fish can completely counteract the neurological benefits provided by these nutrients, and even increase the risk of heart attack.[1,2] This article will discuss the dangers of mercury contamination, the benefits of fish, and strategies to gain these benefits while avoiding mercury.

The danger of mercury in fish

Industries release mercury as an airborne contaminant that eventually accumulates in rivers, lakes, and oceans. As a result, mercury can accrue to high concentrations in the bodies of fish.

Heart attacks: Multiple international studies indicate that people with higher levels of mercury toxicity are more likely to have heart attacks,[2,3] and that the mercury found in fish can accumulate in the body to reach this dangerously high level.[4] 

Impaired mental development: Children and infants are especially susceptible to cognitive impairment resulting from mercury found in fish. When tested, fish-eating Mediterranean children with mercury levels above the FDA limit were found to have impaired memory, verbal ability, and general cognition.[5] These children also experienced delays in their mental development.

Complications during pregnancy: One study demonstrates that pregnant women with high mercury toxicity are more likely to give birth prematurely before 35 weeks.[6] Infants born prior to 37 weeks of gestation are more than twice as likely to experience birth defects.[1,7]

Health benefits of fish that are low in mercury

Uncontaminated fish offers a wide range of health benefits.

Brain health: Fish is low in bad fat, high in protein, and contains beneficial fatty acids. These include omega-3, which is converted DHA, the brain-enhancing compound used for brain growth during infancy and for brain maintenance in adults.[8] In studies, infants who are born to mothers who eat uncontaminated fish during pregnancy have better cognition and faster development.[1,9]

Anti-inflammatory properties: DHA can also help people who have arthritis, depression, high blood pressure, atherosclerosis, diabetes, and thrombosis due to its anti-inflammatory properties.[8,10]

Cardioprotection: DHA can provide protection against heart attacks and cardiovascular disease.[10]

Cleanliness: Compared to beef, pork, chicken, or turkey, wild fish meat is less likely to contain artificial growth hormones or antibiotics.[11]

3 ways to safely eat fish

Fish that contain very low levels of mercury are typically expensive and difficult to find. Here are three ways to get the health benefits you want without the risk.

Wild fish: Generally, ocean-caught or wild-caught fish contain the least amount of mercury, while farm-raised and canned fish contain the most. Wild caught fish or ocean fish are more likely to have eaten a natural diet than farm raised animals that are often fed corn, animal waste, and other unhealthy filler ingredients.[12] If you can find ocean fish or wild-caught fish, one study recommends 4 servings per week for DHA benefits.[9]

Balance: For mothers and infants, the studies mentioned above found a trade-off between mercury damage and DHA benefit. Until a certain level of mercury toxicity is reached, the benefits of fish consumption may outweigh the mercury risks that come with it. One study suggests that pregnant mothers consume 2 to 3 servings of fish per week.[1] This amount was associated with infant DHA levels that were high enough to improve brain function and mercury levels that were too low to cause noticeable detriment.

Supplementation: Fish oil, DHA, and omega-3 supplements can provide many of the benefits of fish without a high risk of mercury exposure. When investigating the mercury content of several purified fish oil supplements, one study found mercury levels to be either negligible or completely non-detectable.[13]

Studies support the benefit of taking 1000 mg of DHA per day for cardioprotective benefits.[14] This dosage is common among DHA capsule supplements. Keep in mind that 1000 mg of omega-3 will not be converted completely into 1000 mg of DHA, making it better to supplement directly with DHA than with omega-3.

Which fish are safe?

Choose fish low in mercury and avoid those with high mercury. One study concluded that canned fish have the highest mercury content of store-bought fish,[6] while another study found that wild-caught ocean fish do not contain enough mercury to cause health problems.[15]

According to the Food and Drug Administration, the following fish and shellfish contain the lowest levels of mercury when fresh and not canned:

• Anchovies
• Catfish
• Clams
• Crawfish
• Oyster
• Salmon
• Sardines

Avoid the following fish with the highest levels of mercury:

• Mackerel
• Tilefish
• Tuna
• Orange roughy
• Shark

Share your experience

Do you know of a great type of fish that is low in mercury? Do you have a favorite supplement? Share your experience in the comments section below.

[1] Environ Health Perspect. 2005 Oct;113(10):1376-80.

[2] N Engl J Med. 2002 Nov 28;347(22):1747-54.

[3] Am J Clin Nutr. 2012 Oct;96(4):706-13. Epub 2012 Aug 15.

[4] Environ Health Perspect. Apr 2003; 111(4): 604–608.

[5] Environ Res. 2010 Jan;110(1):96-104.

[6] Environ Health Perspect. 2007 Jan;115(1):42-7.

[7] J Pediatr. 2001 May;138(5):668-73.

[8] Pharmacol Res. 1999 Sep;40(3):211-25.

[9] Epidemiology. 2004 Jul;15(4):394-402.

[10] Prostaglandins Leukot Essent Fatty Acids. 2014 Apr;90(4):139-43.

[11] Public Health Rep. 2012 Jan-Feb; 127(1): 4-22.

[12] Prev Med. 1997 Sep-Oct;26(5 Pt 1):599-602.

[13] Arch Pathol Lab Med. 2003 Dec;127(12):1603-5.

[14] J Am Coll Nutr. 2006 Dec;25(6):480-5.

[15] JAMA. 1998 Aug 26;280(8):701-7.

[16] Food and Drug Administration.