Eating Fish: Benefits of Omega-3 Outweigh Risks of Mercury

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Because of its rich omega-3 fatty acid content, eating fish is considered to be heart-healthy, but some research has raised concerns about the mercury content of some seafood, which may actually increase a risk of cardiovascular disease. When further investigating this link, researchers from Harvard say that the heart-healthy benefits of fish consumption outweigh the risks of its potential mercury content.

Dietary Guidelines Suggest Two Servings of Fish Per Week

Dariush Mozaffarian MD DrPH, an associate professor of medicine and epidemiology, and colleagues analyzed data from two large studies that included over 170,000 men and women combined. Participants answered questions every two years about their medical history, risk factors, disease incidence, and lifestyle.

Read: High Doses of Omega-3 Might Prevent Obesity Related Disease

The researchers narrowed down the cohort to nearly 7,000 volunteers and measured mercury concentrations in stored toenail clippings, considered excellent biomarkers of long-term mercury exposure. Half of the participants were identified as new cases of coronary heart disease or stroke. These were matched with the same number of healthy controls free of cardiovascular disease.

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In the top quintile of exposure (top 20%), average toenail mercury levels were 0.7 micrograms per gram. For comparison, the current advisory statement is to keep mercury exposure below an amount corresponding to 0.4 micrograms per gram. However, researchers found no association between this higher mercury exposure and a higher risk of cardiovascular disease. The trends toward lower risk was seen, which the researchers attribute to the heart-healthy nutrients found in fish.

"These findings suggest that people need not worry about cardiovascular harm from mercury exposure when deciding whether or not to consume fish," said Mozaffarian.

Read: Pregnant Women Eating Fish Boost Child's Intelligence

"Our results strongly support the recently released 2010 U.S. Dietary Guidelines, which conclude that 'health benefits from consuming a variety of seafood in the amounts recommended [two servings per week] outweigh the health risks associated with methyl mercury' and that most Americans should 'increase the amount and variety of seafood consumed by choosing seafood in place of some meat and poultry,'" said senior author Eric Rimm, associate professor in the Departments of Epidemiology and Nutrition at Harvard School of Public Health.

However, Mozaffarian states that the research does not change the advisory that children or women who are or may become pregnant to avoid eating certain species of fish with higher mercury levels such as shark, swordfish, king mackerel or tilefish. These have the potential for adverse effects on neurodevelopment in children.

The study appears in the March 24, 2011, edition of the New England Journal of Medicine.

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