A study published in this week’s New England Journal of Medicine shows that early childhood exposure to thimerosal, a mercury-based preservative in vaccines, does not lead to a host of neurological impairments.
Researchers from the Centers of Disease Control and Prevention examined mental acuity and behavioral problems in over 1,100 children immunized in the 1990s. At the time of study, the children were between seven and ten years old. They were tested for 42 neuropsychological outcomes including fine motor skills, attention, speech and language skills, verbal memory, behavior regulation and tics, according to this article in the Wall Street Journal.
The researchers did not examine the link between thimerosal and autism, which is the most controversial of concerns. That will be the focus of another research project to be published next year, the WSJ article says.
The results of this week’s study showed “few significant associations with exposure to mercury from thimerosal,” according to an abstract from the original study. The results were kind of a mixed bag with all the associations considered to be small.
Here’s what they found:
Higher prenatal exposure to mercury was associated with better performance on one measure of language and poorer performance on a different measure of attention and executive functioning, the abstract says.
(I was curious about executive functioning. What is that? I looked it up online and found this explanation: “Executive functioning is a set of processes that include ‘planning, organizational skill, maintaining a mental set, selective attention, and inhibitory control – for which the prefrontal regions of the brain are specialized.'” Someone else described it using the metaphor of an orchestra conductor.)
Increasing levels of mercury exposure from birth to 7 months were associated with better performance on one measure of fine motor coordination and on one measure of attention and executive functioning. In addition, increasing mercury exposure from birth to 28 days was associated with poorer performance on one measure of speech articulation and better performance on one measure of fine motor coordination.
The researchers concluded: “Our study does not support a causal association between early exposure to mercury from thimerosal-containing vaccines and immune globulins and deficits in neuropsychological functioning at the age of 7 to 10 years.”
However they did find an increase in motor and phonic tics in boys exposed to thimerosal. According to the WSJ article, “boys in the study who had been exposed to higher levels of the preservative faced twice the risk of having motor and phonic tics — including noises caused by an involuntary tongue movement — than boys who received a smaller dose.” This finding prompted the study authors to say there is a potential need for further studies.
Still, Anne Schuchat, an assistant surgeon general with the CDC, called the results of the new study “very reassuring for parents” whose children were immunized in the 1990s, the WSJ article says. The government asked manufacturers to remove thimerosal from vaccines in 1999, after the public bombarded federal offices with complaints.
I know that people get very passionate about the issue of vaccines. I have always fallen on the side of getting my kids vaccinated, both for their own health and for the common good. I kind of doubt that this study will change the way anyone feels about the issue. According to the WSJ article, the study’s advisory panel included a woman named Sallie Bernard, who is the executive director of SafeMinds, a consumer-advocacy group focusing on mercury’s link to disorders.
The WSJ article says that Bernard dissented from the conclusions, in part, because of the concern over tics in boys. The results, “are inconclusive and the interpretation of the data is too sweeping,” said Ms. Bernard, an Aspen, Colo., parent of an autistic child.
It’s interesting to see that the scientists were willing to include a consumer advocate on their advisory panel. As it turned out, it doesn’t sound like it did much to quiet down the debate.