Blood samples were taken from the children while mothers answered questions about different possible exposures to mercury, such as diet, dental amalgams, thimerosal-containing vaccines and even personal-care products such as earwax removal systems and nasal sprays.
First results showed that children with autism actually had much lower levels of mercury in their blood, but this was explained by the fact that these children ate less fish.
When the results were adjusted for this and other variables, mercury levels came out about the same between the autism group and the control group.
"Not only do we not see differences, but the values are pretty close to national averages," said study author Irva Hertz-Picciotto, chief of environmental and occupational health and a faculty member at the MIND Institute at the University of California, Davis.
Overall, children with developmental delays other than autism had lower blood mercury concentrations.
Children who had mercury-based dental fillings who ground their teeth or chewed gum had blood concentrations of the metal. And those few children who had had a mercury-containing vaccine did not show elevations in their blood levels.
"The relationship between [mercury] intake to blood levels seems to follow the pattern that we expect and it's well known that most of the mercury in the body does come from fish consumption," Hertz-Picciotto said. "There really were very few children who had vaccines that would have or could have contained thimerosal."
Most of the children in the study had received vaccines after thimerosal was removed from vaccines, she said.
Mercury only has a half-life in the circulating blood of a few months, Hertz-Picciotto said, so "clearly this does n
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