Confessions of a Quackbuster

This blog deals with healthcare consumer protection, and is therefore about quackery, healthfraud, chiropractic, and other forms of so-Called "Alternative" Medicine (sCAM).

Friday, March 25, 2005

Revisiting the Thimerosal-Autism Connection

Revisiting the Thimerosal-Autism Connection
by Dr. Michel Cohen

A debate is currently raging in the media over a connection between vaccinations and autism. The main issue is whether thimerosal, a preservative formerly used in many vaccines, is behind the recent rise in documented cases of autism.

Autism used to be viewed as a single type of early-onset developmental disability that affected social and communication skills. In recent years, however, as medicine's understanding of autism has deepened, the affliction has been reframed as a spectrum of disorders of lesser and greater magnitude, ranging from the severe impairments associated with low functioning autism to the more manageable forms of high functioning autism, such as Asperger's syndrome.

Thimerosal is a highly effective preservative and anti-contaminant derived from mercury. It was once common in minute quantities in many medical and ophthalmic solutions, including vaccines and contact lens storage liquids. Yet vaccine manufacturers removed thimerosal from almost all children's vaccines at least five years ago. Thimerosal is still present in some flu vaccines, but thimerosal-free versions have been available for several years.

As recently as last month, the Journal of Child Psychology and Psychiatry published a report by UK and Japanese researchers that disproved the thimerosal-autism connection in a study of 30,000 Japanese kids. The website of the Centers for Disease Control ( offers several studies that refute any linkage. The CDC's own Institute of Medicine's Immunization Safety Review Committee recently concluded that "neither thimerosal-containing vaccines or MMR [measles-mumps-rubella] vaccine are associated with autism" and that "the hypotheses regarding a link between autism and MMR vaccine and thimerosal-containing vaccines lack supporting evidence and are only theoretical."

More to the point: If there were a link between thimerosal and autism, you would expect to see a sharp decrease in autism, since thimerosal has been absent from all childhood vaccines (except some flu vaccines) for five years now, On the contrary, the documented autism rate has continued to climb, proving there is no relationship between the two whatsoever.

Yet in a recent web search on "thimerosal autism," five of the first ten results link to alarmist informational sites bankrolled by law firms. Not to knock my fellow professionals, but this data point makes it easier to understand why there is still so much press on the alleged thimerosal-autism connection. The agenda of many of these sites is quite clear: to link vaccines to autism and to stimulate lawsuits by aggrieved parents. As for the media's ongoing interest in autism, sensationalism seems to be the primary motive.

The Rise of Autism

Autism spectrum disorders afflict as many as one in every 500 children, appearing more commonly in boys. The incidence is growing at an alarming rate. According to the US. Department of Education, in 1992 just under 16,000 Americans ages 6-22 were diagnosed as autistic. That number has risen steadily each year, and in 2003, it was up to just above 141,000 -- a leap of some 800%. What could possibly explain this dramatic increase? Experts, myself included, attribute it to better diagnosis, now that the medical profession is more aware of autism's many forms. And with better diagnosis comes reclassification of patients as autistic.

Consider a recent study in California. That state's Environmental Health Investigations Branch conducted a study of 16,152 kids born between 1987 and 1994. Of those, 5,038 had been diagnosed with full-syndrome autism, while 11,114 had been diagnosed with unexplained mental retardation without autism. The study found that while autism increased by just over .09%, mental retardation decreased by just over .09%.

What Else Then?

Although no one really knows what causes autism, scientists are looking at genetic and environmental problems. A fairly new but well-received theory holds that autism is a form of hyper-maleness, caused by an overabundance of testosterone in the womb. Other potential links include a familial history of depression and / or dyslexia, a weakened immune system, and the presence of a certain form of yeast in the child's intestinal tract. Further supporting the genetic link, identical twins (who share 100% of genetic material) are likelier to both have autism than are fraternal twins (who share only 50%).

Environmental factors such as pollution and toxins have also been advanced as possible causes of higher autism rates, particularly in towns with a history of mining and certain kinds of manufacturing. In short, there are many plausible causes of autism, but no conclusive evidence to identify any one definitively.

Importance of Vaccines

Vaccination and immunization represent one of mankind's most significant recent medical advances. Devastating diseases such as polio, whooping cough, and meningitis, which used to claim the lives of many children, have almost disappeared, thanks to the universal use of vaccines. Other less severe but unpleasant diseases, such as chicken pox and the flu, can now be prevented.

Vaccination has been so successful that most of the diseases we immunize against have become rare. As a result, people tend to focus more on vaccines' possible side effects, rather than on their benefits. Alarmingly, the recent trend away from vaccinations is eroding our vaccine-driven safety net; it is estimated that only 80% of children receive immunizations today.

Try to be discriminating when you read anti-immunization materials. They are often based on pseudo-science trumpeted by agenda-driven doctors and lawyers. By undermining the progress already made toward fully eradicating diseases such as whooping cough or hepatitis, such notions could lead to tragic consequences for your child or even for large numbers of children. When all kids are immunized, diseases cannot leap from child to child to form outbreaks. But as the incidence of vaccination drops, the risk of resurgent childhood diseases rises, imperiling kids and even those adults who were never immunized.


Dr. Cohen lives in New York with his wife and three daughters and brings more than 10 years of Pediatric practice experience to his patients. He has been named in Castle Connolly's Top Doctors: New York Metro Area and America's Top Doctors. He is a regular contributor to and offers advice to parents in his weekly "Ask Dr. Michel" column. For more information on Dr. Cohen, visit his website at