Mercury Fears Allayed (sort of)

by Stacey

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.



Filed under baby, children's health, family, family life, fears, kids, parenting, safety, toddler

3 responses to “Mercury Fears Allayed (sort of)

  1. “The government asked manufacturers to remove thimerosal from vaccines in 1999, after the public bombarded federal offices with complaints.”

    Nope… thimerosal is still in the vaccines, unless a patient specifically asks for thimerosal-free vaccine. I participated in a mass flu-shot “fair” a couple of years ago. We vaccinated a little over 900 people in one day. All of the vaccine bottles we used that day had thimerosal listed in the ingredients. People did not even get the choice of having thimerosal-free vaccines for them or their children.

    And what about University of Calgary’s study about the effects of mercury on neurons? The link will take you to a short video they made that shows what happens when mercury comes in contact with these cells.

  2. Hi Diane,
    I went to the FDA web site to check on your facts. You’re right about the flu vaccine, but that is optional for children. Most of the vaccines that children receive as part of the recommended series no longer contain thimerosal. The following is a quote from the FDA:

    Thimerosal has been removed from or reduced to trace amounts in all vaccines routinely recommended for children 6 years of age and younger, with the exception of inactivated influenza vaccine (see Table 1). A preservative-free version of the inactivated influenza vaccine (contains trace amounts of thimerosal) is available in limited supply at this time for use in infants, children and pregnant women. Some vaccines such as Td, which is indicated for older children (≥ 7 years of age) and adults, are also now available in formulations that are free of thimerosal or contain only trace amounts. Vaccines with trace amounts of thimerosal contain 1 microgram or less of mercury per dose.

  3. If that’s true about the other vaccines, then it’s really good. The journal article must have only referred to flu vaccines when it stated “The government asked manufacturers to remove thimerosal from vaccines in 1999…” since the FDA said some vaccines never contained thimerosal.

    That still makes the statement wrong concerning the flu vaccines, however, since they still contain.
    Even though the flu vaccine is optional for children, it is very strongly encouraged and sometimes mandatory for children enrolled in WIC.
    There are no federal guidelines for ethylmercury (the kind in thimerosal) versus methylmercury. The studies done to compare the two only found that ethylmercury was less neurotoxic than methylmercury. Considering the average half-life of mercury is 70 days and that it can take weeks or even months for it to be excreted out of the body, I’m still not convince that its healthy for anyone, young or old to take it.

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