Mercury has often been blamed for causing many medical disorders and families of children with autism have continued to blame excess levels of mercury in the environment as a cause of this developmental disorder. In the past there have been numerous studies showing elevated levels of mercury in individuals with autism. However, on closer analysis most of the studies were poorly controlled, had few patients and the overall quality of the studies was extremely poor. One of the reasons why mercury has always been a prime suspect of autism was because it was used as a preservative in some vaccines. However, the use of thimerosal was discontinued years ago and but newer cases of autism continue to be diagnosed. In fact, a federally funded study on vaccines containing mercury revealed no connection between autism and the measles mumps vaccine.

Now finally there is a study in the Journal of Environmental Health Perspectives, which found no differences in blood mercury levels between children who are growing normally and those diagnosed with autism.

Says Dr Patricia Mannin Courtney, medical director of the Kelly O’Leary Center for Autism Spectrum Disorders at Cincinnati Children’s Hospital Medical Center, “”This is an excellent study that has addressed a very important question for many families about the role of mercury in autism. It’s a very clear study that no differences in mercury were seen. Is it going to put the questions to rest? I think no. It’s another important contribution to the large body of knowledge on this topic, but I think it will still be an area of great controversy.”

In the present study, researchers followed 452 children between the ages 2 to 5 who either had autism/autism spectrum disorder, developmental delays other than autism (such as Down syndrome), or who were growing normally.

Extensive interviews were done with the parents about diet, use of dental amalgams, thimerosal vaccines and even personal care products. All children had blood samples taken on a regular basis. The initial results in fact showed that autistic children had much lower levels of mercury in their blood but this was clarified by the fact that many of these children consumed less fish.

After adjusting for all confounding variables, results of the study showed no difference in mercury levels between autistic children and normally growing children.

“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 faculty member at the MIND Institute at the University of California, Davis. Since mercury does not stay in the body for more than a few months, Hertz-Picciotto added “clearly this does not tell us anything causal because all of the mercury represents exposure that had happened post-diagnosis.”

While the study did show that levels of mercury are not high in children who have already been diagnosed with autism, it is still not known whether prior exposure to mercury during pregnancy or during the first year of life may have initiated the disorder. But at least for now, there is no question that mercury levels are lower in people who have developmental disorders.