Health officials have long advised consumers to balance the benefits of eating fish, and particularly omega-3 rich oily fish, with the risk of potential mercury exposure from doing so. Some fish, including swordfish, tilefish, king mackerel, and some shellfish, tend to store more methyl mercury in their flesh than other species.
The study’s authors, from Harvard School of Public Health and Brigham and Women's Hospital in Boston, said that the main health concern in adults has been potential cardiovascular toxicity, as suggested by results of animal studies and limited studies in humans. But the researchers found no increased risk of cardiovascular disease in their review of two cohort studies with a total of more than 170,000 participants.
“We found no evidence of any clinically relevant adverse effects of mercury exposure on coronary heart disease, stroke, or total cardiovascular disease in US adults at the exposure levels seen in this study,” they wrote.
Pregnant women and children
However, the authors said that the current recommendation still stands that pregnant and nursing women, infants and young children should avoid eating more than two servings of fish per week, and limit intake of certain species that are higher in methyl mercury, because of a possible link between chronic, low-level methyl mercury exposureand “subtle but measurable neurodevelopmental delay in infants.”
This is largely in line with the recently released 2010 Dietary Guidelines for Americans, which said that for the general adult population, the health benefits of eating a variety of seafood outweigh any health risks associated with methyl mercury – and that pregnant and breastfeeding women should eat at least eight ounces, but no more than 12 ounces of fish per week, from choices that are lower in methyl mercury.
Meanwhile for the general adult population, the authors of this latest study said: “Higher mercury exposures were actually associated with trends toward lower cardiovascular disease risk.”
They said this slightly lower heart disease risk said was most likely a result of other nutritional benefits of fish consumption.
The researchers examined data from two separate cohort studies involving 173,229 people about their medical history, risk factors, disease incidence, dietary habits and lifestyle. They also measured mercury concentrations in stored toenail clippings – known to accurately reflect mercury consumption – of nearly 7,000 participants, an equal number of whom had or had not suffered from cardiovascular disease or stroke during the study follow-up period.
Source: New England Journal of Medicine
2011, Vol. 364, pp. 1116-25
“Mercury Exposure and Risk of Cardiovascular Disease in Two US Cohorts”
Authors: Dariush Mozaffarian, Peilin Shi, Steven Morris, Donna Spiegelman, Philippe Grandjean, David S. Siscovick, Walter C. Willett, and Eric B. Rimm