By Ed Edelson
HealthDay Reporter

Although new research links mercury in seafood with high blood pressure, this isn't reason enough for most people to stop eating fish, the study leader says.

"The small increase of blood pressure due to methylmercury will never outweigh the benefits of omega-3 fatty acids," said Dr. Eric Dewailly, a professor in the department of social and preventive medicine at Laval University in Quebec and lead author of a report in the Oct. 5 issue of Hypertension.

Diets rich in omega-3 fatty acids from oily fish, such as fatty sardines, herring, trout and salmon, are associated in many studies with a reduced risk of death from heart attack, stroke and other cardiovascular disease. The American Heart Association recommends eating two meals a week containing four to six ounces of such fish.

But because fish can contain high levels of methylmercury, which can interfere with the normal development of the nervous system and brain in fetuses and newborns, the U.S. Food and Drug Administration advises pregnant women, those trying to get pregnant, nursing women and children to limit their fish intake.

FDA guidelines limit intake of low-mercury fish for those individuals to 12 ounces a week and high-mercury fish to three 6-ounce servings a month. The FDA also advises avoiding fish most like to carry the highest levels of mercury -- shark, swordfish, king mackerel and tilefish.

At first glance, the Canadian study appears to add high blood pressure to the list of problems linked to methylmercury in fish. Dewailly and his colleagues conducted a survey of Inuit residents of 14 Nunavik communities in northern Quebec, where the traditional diet is based on fish and marine mammals.

It found an average blood mercury level of 50 nanomoles per liter of blood, much higher than the 4-nanomole level of the general U.S. population. It also found a relationship between blood mercury levels and blood pressure after adjusting for other factors, such as smoking and physical activity.

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."