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Between 20% and 30% of mainstream Canadian women of reproductive age have mercury levels high enough to damage the brain of a developing fetus, a University of Western Ontario study has found.
While developing babies won't be hurt in many cases, the findings are a concern, said Dr. Gideon Koren, Ivey Chair in Molecular Toxicology at Western's Schulich School of Medicine and Dentistry.
The main source of the mercury is fish consumption, he said.
A troubling part of the study was that many of the women thought their fish consumption was within health guidelines.
Koren said guidelines, such as Health Canada's recommendation that women have only two servings of fish a week, are of little use because the mercury levels in fish can vary widely.
"They are not meaningful. We should not use numbers in science or in public health that are meaningless," he said.
The dilemma women face is that while fish consumption increases mercury levels, it is also considered an important source of omega-3 fatty acid during pregnancy.
"This is the worst case possible for public health," said Koren.
More than 100 women were tested for mercury levels, using hair samples that were analyzed at London Health Sciences Centre.
The study confirmed there was a strong correlation between the amount of fish consumed and the mercury levels in the body.
The women in the study with the highest concentrations, well above the level where harm might occur, was in Japanese Canadians, a group that consumes much more fish than mainstream Canadians.
Koren is recommending women who might be at risk for higher mercury levels be tested.
If their level is high enough to possibly cause damage to a developing fetus, a change in diet can be recommended, either reducing fish consumption or shifting to fish with lower mercury content, he said.
"If a woman is high, we can do something about it," Koren said at the annual Ivey Symposium on EcoHealth Toxicology.
The study looked specifically at methylmercury, the most toxic form to humans that is almost completely absorbed into the bloodstream.
While adults may show no adverse effects at low levels, the mercury can cause neurological damage to developing fetuses.
John Miner is The Free Press health reporter.
john.miner@sunmedia.ca