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Study adds to evidence against autism-mercury link

In one of the largest studies yet, UC Davis researchers said Monday they found no real difference in blood-mercury levels of children with, and without, autism.

The study, published in Environmental Health Perspectives, measured blood mercury levels of 452 children, 249 who had autism. Children with autism had lower levels, but it was because they eat less fish. Once researchers took fish consumption into account, the difference disappeared.

The levels were similar to what has been found in national samplings of children covering a similar age range.

"It's a pervasive belief that children with autism have tons of metal in them," said co-author Irva Hertz-Picciotto, an environmental epidemiologist at UC Davis. "We could not measure levels in brain or other tissues, but mercury concentrations circulating in the blood of children with autism were similar to levels in other children."

Hertz-Picciotto cautioned that the study only measured current mercury levels in the children, not exposure that may have happened earlier in life.

"This isn't a study asking whether mercury causes autism," she said.

High levels of mercury exposure have been known to cause severe neurological damage, and there have been hypotheses pointing to mercury as one of the possible causes of autism.

The number of autism diagnoses, characterized by abnormal social interactions and communication, has increased dramatically in past decades.

A study released this month in the journal Pediatrics estimated autism's prevalence to be 1 in 91 children, an increase from 1 in 150 children, reported by the Centers for Disease Control and Prevention in 2008.

The study released today is part of a large, Sacramento-based study that seeks to cast a wide net over environmental and genetic factors in relation to autism. The study, called Childhood Autism Risks from Genetics and the Environment Study (CHARGE), has enrolled over 1,000 children since its inception in 2003.

There is a great need for credible research in the arena of autism and the environment, experts said.

"It's a problem that the issue of environmental factors has not been researched to the degree it needs to be," said Lee Grossman, head of the Maryland-based Autism Society.

The comprehensive nature of CHARGE will help guide clinicians, said Antonio Hardan, who is director of Stanford Medical School's Autism and Developmental Disabilities Clinic.

"There have been similar studies but not as good as this one," he said. "This will really add to the literature."

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