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Kids Exposed to Mercury, Lead at Risk for ADHD

Mercury and Lead Linked to More Symptoms of ADHD continued...

In contrast, Inuit children with even low to moderate blood levels of lead -- closer to levels measured in some U.S. children -- were more than four times more likely to have problems with hyperactivity than kids with lower lead levels.

"The effects we are seeing are at very low levels of exposure. In [the] U.S. and Canada, for example, we estimate that 10% of children would be exposed to [these] blood lead levels," says Muckle. U.S. children can be exposed to lead when they eat tiny chips of lead-based paint, which can be found in homes built prior to 1978.

The study is published in Environmental Health Perspectives. It was paid for by government grants from the U.S. and Canada.

Mercury Exposure Before Birth

Other studies that have looked for a link between mercury exposure and ADHD have had mixed results. A study of children in the Faroe Islands, where marine mammals like whales are dietary staples, also found attention problems in school-aged children exposed to high levels of the heavy metal before birth.

But another study, of children in the Seychelles Islands, found no clear link between mercury exposure before birth and behavior problems.

"It's quite an interesting sort of finding, really. In the Seychelles they found that the more mercury exposure before birth, the higher the child's IQ. In the Faroe Islands, the more mercury, the worse off the kids were," says Justin Williams, MD, a psychiatrist at the University of Aberdeen in Scotland. Williams was not involved in the study.

Williams says the differences may come down to the source of the mercury. In the Seychelles, pregnant mothers were getting mercury through diets high in fish. Fish is also high in essential fatty acids that may protect developing brains. In the Faroe Islands, mothers got mercury by eating marine mammals, which lack the protective fatty acids found in fish.

"As always, you have to look at these studies and be very cautious, really. What we may find is that mercury is a marker for someone else. It's not necessarily a causal relationship," he says.

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