Autism does not appear to be linked to a preservative present in some childhood vaccines, according to a Danish study.

The study looked at thimerosal, which contains mercury, and analysed 30 years of data.

"Thimerosal has been eliminated from childhood vaccines in most industrialized countries," said Dr. Kreesten Meldgaard Madsen, the lead author. "If indeed thimerosal was an important cause of autism, (autism rates) should soon begin to decline in these countries. We did not see this decline."




Autism is a developmental disorder with various symptoms including impaired communication skills and social interaction and repetitive behaviours such as finger tapping.

Vaccine makers in the U.S. began phasing out thimerosal a few years ago after pressure from public health officials and parent groups. Mercury can cause neurological damage.

The U.S. Institute of Medicine did a thimerosal review in 2001. It said the potential link between thimerosal and neurodevelopmental disorders was unproven but medically plausible. It recommended more research.

Danish scientists looked at data on 956 children diagnosed with autism from 1971 to 2000. They said the rate climbed steadily from one child per 1,000 in 1990 to nearly five per 1,000 in 1999. That's seven years after thimerosal was removed from vaccines in the country.

The study is published in the journal Pediatrics.

The report has done little to allay fears in the U.S. about thimerosal and vaccines.

Mark Blaxill of the Safe Minds activist group said it's not surprising where the study is published since the majority of readers of Pediatrics are pediatricians who administer vaccines.

Safe Minds was founded by parents of autistic children. It seeks to raise awareness about the risks of mercury.