Studies have shown that exposure to environmental mercury can affect the endothelium, the delicate lining of blood vessels, and decrease the ability of smooth muscles to relax, which could explain the slight increase in blood pressure seen in the study, Dewailly said.
It was not a great effect, he said. "For every 10 percent increase in blood mercury level, there is a 0.2 millimeter increase in blood pressure," Dewailly said. "Even if you apply that to an entire population, that is a small effect."
So, a 10 percent increase in blood mercury would raise a blood pressure reading from 120/80 to 120.2/80, Dewailly indicated. That is not a reason to avoid fish "if you look at the fish nutrients that are reported to be associated with so many benefits," he said.
But it's important to eat the right kind of fish, the oily species, Dewailly said. Anyone worried about blood pressure should avoid fish that have low levels of omega-3 fatty acids and high mercury content, such as big predator fish, including swordfish, marlin and shark, he said.
Another heart expert concurred.
"Many Americans can safely enjoy eating fish as a regular part of their diet to achieve the health benefits of omega-3 fatty acids," said Penny Kris-Etherton, distinguished professor of nutrition at Pennsylvania State University and a member of the American Heart Association Council on Nutrition Metabolism and Physical Activity Committee.
"And this includes canned light tuna, which is significantly lower in mercury than white tuna," she said in a statement.
Benefits of omega-3 fatty acids are described by the American Heart Association.'/>"/>
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