Green Buckeye RN

Medscape Nurses: Mercury/Blood Pressure Link Should Guide Fish Choices
October 9, 2009, 10:08 am
Filed under: News, Spotlight on... Mercury

October 7, 2009 (Dallas, Texas) — An association seen between mercury levels and blood pressure (BP) in a recent analysis [1] has researchers warning physicians and consumers about the need to weigh the risks and benefits of fish consumption and to choose with caution the type of fish they eat.

In an analysis of 732 Nunavik Inuit men and women–the indigenous people of northern Quebec–Dr Beatriz Valera (Centre de Recherche du CHUQ, Quebec, QC) and colleagues found mercury levels to be more than 50 nmol/L. That’s more than 10 times higher than levels in the general US population in the National Health and Nutrition Examination Survey (NHANES) study of 4 nmol/L, an American Heart Association (AHA) press release notes [2]. These higher levels stem largely from the preponderance of fish and marine mammals in the traditional Inuit diet, Valera et al point out in their paper, which appears online October 5, 2009 in Hypertension. Mercury levels become more concentrated higher in the marine food chain, with the highest concentrations seen in predators that over the course of a lifetime consume smaller species that have also absorbed environmental mercury from algae and bacteria.

According to Valera et al, mean blood-pressure and pulse-pressure levels were elevated in the Inuit adults studied, and tellingly, mercury was strongly associated with systolic BP levels in multivariate analyses. Every 1% increase in blood mercury levels was associated with a 0.02-mm-Hg increase in systolic BP, they write. An association with diastolic BP was also documented but did not reach statistical significance. Strikingly, the adverse blood-pressure effects of mercury persisted when the purported benefits of fish consumption were taken into account–namely omega-3 fatty acids and selenium.

In the paper, the authors acknowledge that their paper is only one of many that have attempted to characterize the cardiovascular toxicity of mercury, but they believe it to be the first to take into account omega-3s and selenium in an analysis of BP effects of mercury. These fish nutrients, they write, “had a strong confounding effect, suggesting that not adjusting for these substances could lead to an underestimation of the effect size.”

“Our results suggest that eating large quantities of species containing a high mercury content and low omega-3s such as big predator fish–tuna, swordfish, marlin, sharks, etc–is not a good idea for our health,” study coauthor Dr Eric Dewailly (Centre de Recherche du CHUQ) commented in a press release.

In the same release, however, the AHA, which recommends people eat oily fish two times per week, tries to put the results in perspective. “Many Americans can safely enjoy eating fish as a regular part of their diet to achieve the health benefits of omega-3 fatty acids, and this includes canned light tuna, which is significantly lower in mercury than white tuna,” the release quotes Dr Penny Kris-Etherton (Pennsylvania State University, University Park), of the AHA’s Council on Nutrition Metabolism and Physical Activity Nutrition Committee.

While children and nursing mothers should steer clear of fish with the highest mercury contamination (shark, swordfish, king mackerel, or tilefish), the US Food and Drug Administration ( FDA) has said that the benefits of fish consumption outweigh the mercury risks in middle-aged and older men, plus postmenopausal women, the AHA notes.


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