Pregnant women who eat seafood high in mercury could be causing permanent damage to their children, researchers said Friday.

An international group of researchers found diets high in contaminated seafood can cause permanent brain and heart damage in the unborn.

"We found that both prenatal and postnatal mercury exposure affects brain functions and that they seem to affect different targets in the brain," said Philippe Grandjean of the department of environmental health at the Harvard School of Public Health.

Chunk tuna tends to have more mercury than wild salmon
Chunk tuna tends to have more mercury than wild salmon

"The fact that the current exposure has an additional effect, despite the low mercury concentrations is worrisome, especially for communities where seafood constitutes an important part of the diet," Grandjean added in a statement.

The researchers studied more than 1,000 mothers and children living in the Faroe Islands, in the North Atlantic Ocean between Norway and Iceland.

The islands' economy is focused on fishing and the population's diet includes a high intake of seafood and whale meat.

The researchers measured mercury in the cord blood when the children were born, as well in hair samples taken at ages seven and 14.

Grandjean and his colleagues put electrodes on the children's heads to measure electrical signals in the brain.

The scientists found the higher the mother and child's mercury levels were at birth, the more they saw delays in brain signalling.

The brain changes also seemed to lead to poorer heart function, such as subtle differences in controlling blood pressure.

The study appears in Friday's issue of the Journal of Pediatrics.

The report comes at the same time as a U.S. Environmental Protection Agency study doubled its estimates of how many newborns have unsafe levels of mercury in their blood.

Regulatory agencies have to balance concerns about mercury exposure with the heart-healthy nutrients in fish.

Scientists continue to debate whether low levels of mercury in seafood are harmful and if results from people eating a whale-rich diet extends to other populations.