Mercury, Selenium, Omega-3 Fatty Acids and Canned Tuna

The issue of mercury contamination in fish remains in the news. New studies are being published that give significant new information on both the mechanisms of mercury contamination and the human health implications of current mercury standards. Unfortunately, it appears that all the subsequent media attention has resulted in a generalized backlash against seafood consumption, with negative health implications for some.

Numerous health benefits from seafood consumption have been documented over the past ten years or so. Consumption of omega-3-rich fish is proven to lower risks of cardiac, cardiovascular and eye diseases, and to mediate mood, attention and dementia disorders. Pregnancy diets rich in omega-3 fatty acids help to prevent pre-term births, and a study appearing in the March 2008 American Journal of Epidemiology demonstrated that children of women who consumed the most low-mercury, omega-3-rich fish while pregnant – specifically canned tuna- scored the highest on intelligence and motor-skills tests. Additionally, a 2007 study published in The Lancet, a leading British medical journal, concluded that avoiding dietary omega-3’s during pregnancy has a measurable detrimental health effect: Children whose mothers eat no fish during pregnancy are 29 percent more likely to have abnormally low IQs.

This latter effect may be occurring as an unfortunate result of over-reaction about the threat of mercury contamination by some environmental organizations and then by people who read the resulting headlines. In fact, there are questions about the validity of the EPA and FDA mercury criteria. The EPA included a 1,000-percent safety cushion during the formulation of its methylmercury “Reference Dose” – the maximum level of continuous lifetime exposure believed to be without risk of harm. The FDA set its minimum action level for mercury in commercially available fish to limit consumers’ exposure “to levels 10 times lower than the lowest levels associated with adverse effects,: which is, in effect, a ten-fold safety factor that is not based on actual scientific data. Many researchers and medical professionals believe that new information supports revision (upward) of U.S. mercury criteria, or at least co-consideration of other critical factors involved, such as the health benefits of seafood and problems with some early mercury studies. Recent work has shown that a mineral nutrient that is prevalent in fish, selenium, reduces the uptake of mercury in consumers. One study stated that “measuring the amount of mercury present in the environment or food sources may provide an inadequate reflection of the potential for health risks if the protective effects of selenium are not also considered.”

In the meantime, some people have stopped eating fish. One seafood promotion group has developed information on canned tuna, in particular. Canned tuna is the cheapest and most readily available source of omega-3 fatty acids in the United States. For many low-income families, canned tuna is the only consistently affordable source of dietary omega-3 fatty acids. Survey data show that in 1999, 80 percent of low-income American households were buying canned tuna. By 2006, and after much news about mercury in tuna, that number had dropped to 69 percent – a decline of about 4.4 million households. During those years, women in those households gave birth to nearly 260,000 children who were put at risk of developmental problems due to lack of dietary omega-3s in their mothers’ diets. The seafood group noted that cost was probably not a primary factor in the move away from canned tuna, since its price rose only about 1 percent during that period.

Source: Lagniappe (Louisiana Sea Grant) Vol 32 No 11

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