The amount of mercury in the body is directly associated with risk of heart disease, shows an international study published in prestigious journal "The New England Journal of Medicine".
The study, which included several hundred people from nine countries showed that current levels of mercury in some fish species undo the beneficial effects of certain fatty acids (such as the type of Omega3 fatty) and may increase the risk of an heart attack.American experts from FDA recommend consumers to continue to eat especially fish and seafood in which mercury level is not so high: sardines, salmon and shrimp. Although fish is recommended as a healthy food, these species assimilating amounts of mercury in their bodies that can cause birth defects in fetuses. Researchers believe that a pregnant woman can eat fish but only to vary the species from menu as much they can, from molluscs to small oceanic fish .
Mercury normally present in rocks, lakes, streams and oceans, and also the one added by human activity, changes under the action of bacteria in an organic form, much more toxic, called methylmercury.This one, is much easier to fix in tissues and accumulates in fish meat, thus achieving very high levels. Acceptable limit of the concentration of methylmercury in fish meat sold is 0.5 parts per million (ppm). Following measurements revealed that, in general, meat shark, swordfish or tuna (fresh or frozen) has a concentration ranging between 0.5 and 1.5 ppm.
It is not the case with preserved tuna, whose concentration is limited to 0.5 ppm revealed by the tests made at the time of processing, but that usually for canned fish which are smaller, younger, so they do not have time to accumulate methylmercury toxic doses in their tissues. It isrecommended that these types of fish to be consumed not more than once a week, and in pregnant women and small children, not more than once a month.