Feb 16 2012

Mercury Still Not Correlated with Autism

Another study, published recently in PLoS One, fails to show a correlation between mercury and autism. This was a study of mercury excretion in the urine, comparing subjects with autism to their siblings as well as controls without autism spectrum disorder (ASD), both in mainstream and special schools. They found no significant difference among the groups, even controlling for kidney function (creatinine clearance), age, gender, and amalgam fillings.

To put this study into context – there are those who claim that mercury toxicity is what causes ASD, and in fact ASD is simply misdiagnosed mercury toxicity. There is no question that mercury is indeed a neurotoxin, but toxicity is all about dose, so the question is are children being exposed to mercury in high enough dose to cause toxicity. Further, it is difficult to extrapolate from preclinical studies (in test tubes and petri dishes) to living organisms. We need to further know what happens to the toxin in the body, and how the body handles it.

With regard to the forms of mercury found in some vaccines (although much less than in previous years) and tuna fish, the body seems to rid itself of the mercury sufficiently quickly to prevent build up to toxic levels. Of course, this remains a hot topic because of the persistent claims by the anti-vaccine movement that vaccine cause ASD, and some who cling to the discredited notion that it is mercury in vaccines that is the culprit. There are also the so-called “mercury militia” who blame environmental mercury (from vaccine and elsewhere) on all human illness, not just autism.

As further background, it’s helpful to note the chain of argument that has occurred with respect to the role of mercury in autism. Studies have consistently found no correlation between mercury exposure and the risk of ASD. Proponents of the mercury hypothesis have therefore argued that there is a subpopulation of vulnerable children who metabolize and excrete mercury differently than the general population, and it is within this subpopulation that mercury causes ASD.

Logically this may be true, but the argument is little more than special pleading, although a common one. Scientists are familiar with the usual list of special pleading arguments made to dismiss negative evidence. These include: that the dose studied was too low, the treatment duration was too short, the placebo or comparison treatment was also effective, or the looked-for effect only exists in a subpopulation. Each one of these arguments is logically consistent – if true they would explain the negative results without meaning that the phenomenon is not true. They may even be true in specific cases. What makes them special pleading is when they are invoked ad hoc to explain negative evidence without good justification.

With respect to mercury and autism, when studies failed to show a correlation proponents argued that only a subpopulation are vulnerable to mercury toxicity because (they speculated) they have impaired mercury excretion. That is the context for this study – if this particular instance of special pleading were true, then children with ASD would be more likely to have decreased excretion of mercury in their urine. Alternatively, if they are being exposed to more mercury as the cause they would have increased excretion of mercury in their urine. The study found no difference – no increase or decrease in mercury in the urine of children with ASD vs controls.

The authors are appropriately cautious in their conclusions. They say simply that their study does not provide support for the mercury hypothesis (not that it proves it wrong), and further they acknowledge that their study is modest in size (56 children with ASD and 197 total controls). A larger follow up study would be more definitive. But when we add this study to the existing body of research showing a lack of correlation between mercury and ASD it does add to our confidence in this lack of correlation.

Still, in my opinion, the most damning evidence for the mercury hypothesis is the fact that after the removal of thimerosal (which is mercury-based) from the routine childhood vaccine schedule in the US in 2001-2002, there was no subsequent drop in the rise in ASD incidence. Proponents predicted (correctly) that there should be if their claim was correct. Autism diagnoses continue to rise – now a full decade after the removal of thimerosal from the routine vaccine schedule. The supply of special pleading, however, is endless.

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16 responses so far

16 Responses to “Mercury Still Not Correlated with Autism”

  1. locutusbrgon 16 Feb 2012 at 9:57 am

    So an Ideological conviction has failed again to be predictive, and requires special pleading. Not surprising, hopefully it will pull a few away from the dark side. More likely anti vax-autism believers will next say it is not poor mercury clearance but hypersensitivity to mercury.
    When you have a completely one sided stack of good evidence, and it is not convincing to people, adding one more layer will not likely sway them from their stack of cowpies. As a resident of a state that has had a recent measles outbreak I am becoming more and more concerned about this particular brand of baseless speculation/nonsense.

  2. nybgruson 16 Feb 2012 at 10:12 am

    spot on locustbrg. If all the reason and science to date won’t convince you, another 10 studies won’t either.

    can anyone say “zombie?” Or more accurately, The Black Knight

  3. Steven Novellaon 16 Feb 2012 at 10:38 am

    Of course most true believes are beyond evidence. The goal of spreading this information is to inform the vast uncommitted general population who may be hearing misinformation from the pseudoscience side.

  4. locutusbrgon 16 Feb 2012 at 3:10 pm

    Sorry I was not trying to belittle your efforts Dr. Novella, they are laudable. Despite my negative tone I applaud what you are doing. I regularly re-post your blog to my public Facebook page. I print hard copies which I leave for reading in my waiting room. Particularly on this type of topic. It is my small effort to drive a wedge into this topic. Your large effort, and work is appreciated.
    It was more an expression of frustration in general on this topic, and how effective the misinformation has been distributed/accepted. Although I know this is probably just confirmation bias, I am no longer sure that there is a large number of uncommitted on this topic. All too often I find more and more people accept at least part of what mercury/anti-vax proponents have to say. Plus vaccine preventable disease is increasing.
    Frustrating, if you can’t get a majority of people on board with a science success story like vaccines, what chance do we have with the vast majority of pseudoscience?

  5. Woodyon 16 Feb 2012 at 3:31 pm

    Speaking of cowpies, here is a nice malodorous example from the recent literature:

    http://www.ncbi.nlm.nih.gov/pubmed/21797771

    The claim is that autism is more common in descendants of individuals with pink disease (mercury toxicity), with several hand-waving explanations of why that may be. It is worthwhile reading the article to see the methodological flaws (survey questions bias towards the desired response, especially in the targeted survey population; lack of clinical confirmation of ASD cases reported – just to name a few). If you look at the other Pubmed hits for the two authors, their bias is quite clear.

    It doesn’t help their case that they cite research from the now infamous Geiers in the paper…

  6. lizditzon 16 Feb 2012 at 7:14 pm

    Woody, the paper

    J Toxicol Environ Health A. 2011 Sep 15;74(18):1185-94.
    Ancestry of pink disease (infantile acrodynia) identified as a risk factor for autism spectrum disorders.
    Shandley K, Austin DW.

    PMID: 21797771

    Was discussed at LeftBrain/RightBrain by Sullivan (a PhD physicist & autism parent who often eviscerates pseudoscience papers on autism):

    http://leftbrainrightbrain.co.uk/2011/07/ancestry-of-pink-disease-infantile-acrodynia-identified-as-a-risk-factor-for-autism-spectrum-disorders/

    The conclusions of this paper have some major logical hurdles to overcome, to say the least. And this is even before the methods are addressed. For example, this all hinges on reports by the grandparents. Not on an actual prevalence measure of the decendents.

    If is already well established that the rise in mercury exposures from childhood vaccines was not the cause of the rise in autism prevalence estimates. It has always been clear that autism is not similar to mercury poisoning symptoms. The mercury hypothesis has been harmful, both to public health and the autism communities The time for papers which pose intriguing questions on this subject has past. Studies with weak methods and poor logic are irresponsible in today’s world.

  7. Mlemaon 17 Feb 2012 at 1:11 am

    Even though there’s no apparent link between mercury and autism, I’m glad the mercury was removed from vaccines. But their may still be a link between vaccines and autism (from what I’ve been able to learn) You scienc-y types will make better sense of this than I can, but the following article talks about how vaccines may affect the brain:

    http://www.rescuepost.com/files/theoretical-aspects-of-autism-causes-a-review1.pdf

  8. BillyJoe7on 17 Feb 2012 at 5:05 am

    “But their may still be a link between vaccines and autism”

    The MMR vaccine had not been proven to cause encephalitis:

    http://www.fda.gov/BiologicsBloodVaccines/Vaccines/QuestionsaboutVaccines/ucm070425.htm

    Encephalitis has been reported approximately once for every 3 million doses of MMR vaccine. Post-marketing surveillance of more than 400 million doses distributed worldwide (1978 to 2003) indicates that encephalitis is rarely reported after MMR vaccination. In no case has it been shown conclusively that encephalitis was caused by a vaccine virus infection of the central nervous system.

    And, as far as I know, it has not been proven that encephalitis causes autism.

  9. ChrisHon 17 Feb 2012 at 2:50 pm

    Mlema, there are some issues with that paper. Many outlined in this article from Orac.

    Some of those issues are reliance on research from the Geiers, DeSoto, Jepsen, and others. Many in less than reputable journals like Medical Hypothesis, Alternative Medical Review and “Sentient
    Publications.”

    She seems to have ignored more recent and relevant research like:

    Pediatrics. 2010 Aug;126(2):263-9. Epub 2010 Jul 19.
    Lack of association between acellular pertussis vaccine and seizures in early childhood.

    Pediatrics. 2010 Jun;125(6):1134-41. Epub 2010 May 24.
    On-time vaccine receipt in the first year does not adversely affect neuropsychological outcomes.

    Pediatr Infect Dis J. 2010 May;29(5):397-400.
    Lack of association between measles-mumps-rubella vaccination and autism in children: a case-control study.

    Pediatrics, February 2009, Vol. 123(2):475-82
    Neuropsychological Performance 10 years after Immunization in Infancy with Thimerosal-Containing Vaccines

    PLoS ONE 2008; 3(9): e3140 doi:10.1371/journal.pone.0003140
    Lack of Association between Measles Virus Vaccine and Autism with Enteropathy: A Case-Control Study.

    Pediatr Infect Dis J. 2006 Sep;25(9):768-73.
    Encephalopathy after whole-cell pertussis or measles vaccination: lack of evidence for a causal association in a retrospective case-control study.

    I believe the term for what Ratajczak did in that paper is “cherry picking.” Though she did leave us with the unforgettable homologous recombinaltion tiniker!

  10. Woodyon 17 Feb 2012 at 3:09 pm

    @lizditz – thanks for the link. I have “lurked” on LBRB, but somehow managed to miss Sullivan’s takedown of the Pink disease article.

    I just had an interesting thought – has anyone compared developmental outcomes of autistic children who adhered to the recommended vaccine schedule after diagnosis compared to those who did not? My hypothesis is that there would be no difference between the two groups. If the anti-vax theory that autistic children are somehow more susceptible to vaccine injury than other children holds any water, then the children who continued to receive their vaccines should have worsened dramatically, right? Not that such a study would dissuade the hardliners, but it would be fairly easy to do.

  11. Mlemaon 17 Feb 2012 at 10:18 pm

    Chris H.,
    I thought Ms. Ratajczak’s attempt to thoroughly review the literature over several decades and look for some correlation between various environmental factors and the incidence of autism was a thoughtful enterprise. Personally i think she should have included diet along with vaccines and the proliferation of toxic chemicals in the environment. I cannot comment on the conclusions she’s drawn, but I don’t think her intent in drawing them was stilted toward anti-vaccine sentiment. The brain is adversely affected by the very diseases we seek to prevent with vaccines, and when side effects from vaccines are documented, they often include the type of damage that is caused by the diseases they seek to prevent.

    Sorry to link you to another article, but this one talks about why the link between vaccines and autism lingers:
    http://www.huffingtonpost.com/david-kirby/autism-vaccine-_b_817879.html

    “…complex seizures, demyelinating disorders and mitochondrial “meltdowns” have all been implicated in autistic regression. All three can happen in nature without vaccines being involved. In fact, all three can be triggered by childhood illnesses that are prevented by vaccines.

    In that sense, it’s likely that some children have avoided autistic regression precisely because of their immunizations. On the other hand, if vaccines generally prevented ASD, rates would have gone way down since 1988, and not in the opposite direction.

    A good example is ADEM, or acute disseminated encephalomyelitis, in which the brain’s myelin sheath is severely damaged, usually only temporarily. The U.S. Vaccine Injury Compensation Program (VICP), better known as “Vaccine Court,” has ruled that HepB, MMR and other vaccines can result in ADEM and other demyelinating disorders. In one case, Bailey Banks, the VICP found that MMR-induced ADEM resulted in Pervasive Developmental Disorder-Not Otherwise Specified, which is an ASD.”

    “…In another successful VICP case, the special master found that the MMR vaccine had contributed to ADEM, as well as GI distress.”

    This isn’t about getting rid of vaccines. God no! But it’s about trying to find out what’s going on with autism rising. Looking at trends and considering all the other things that may have been going on environmentally, as well as the timing of onset, is one attempt to find causes.

    Is it possible that Ratajczak didn’t include the research you mentioned in her survey was because it was published as she was concluding her own?
    I thank you for the references and the Orac article. i have to admit the article was a little hard for me to read because of the overly-dramatic tone, and the low-brow insults to Ratajczak. I’m not familiar with all the back and forth on this autism-vaccine debate (it’s only an issue for me because it’s growing so prevalent in our society) But when I read an article like that that just seems to take glee in frank insults to someone who worked hard on something (which may have failed) it tends to turn me away from whichever stance it’s promoting. Also, the whole thing of someone slamming the editors of any journal that publishes something that someone doesn’t agree with just seems like too easy of a way to dismiss someone’s proposition.

    I guess i understand why people get so offended by the vocal “anti-vaxers” – it seems like they’ve already made up their minds about something that hasn’t been proven. But I hardly think that saying we haven’t disproved the link between autism and vaccines is like saying we haven’t disproved the link between fairies and autism. That’s just a way to throw a jab at “the other side”. I guess we have to have our fun!

    Thanks again for the info :-)
    Please feel free to point out further misunderstandings on my part with this topic. It’s incredible to be able to learn so much about autism in this brief interlude. Looks like Dr. Novella has a new post about it tonight!

  12. ChrisHon 18 Feb 2012 at 2:37 am

    I thought Ms. Ratajczak’s attempt to thoroughly review the literature over several decades and look for some correlation between various environmental factors and the incidence of autism was a thoughtful enterprise

    She did not thoroughly review the literature. That was noted by how much she missed, as I said. That is what I notated by posting papers she ignored. And I did not get them from the Orac article, but by actually searching the PubMed index.

    And if her article was published in 2011, why did she ignore papers written between 2006 to 2009?

    An article by David Kirby on the Huffington Post is not real scientific literature. For one thing he only sold travel articles to the New York Times, and he has no experience as a science writer.

    In that sense, it’s likely that some children have avoided autistic regression precisely because of their immunizations.

    Citation needed. And by this I mean the journal, title and date of the PubMed indexed article. And please make sure it is not from an researcher who has had their license to practice medicine legally challenged, nor from a journal with a name like “Medical Hypotheses.” If you want to know why, just look up the definition of the word “hypothesis.”

  13. Mlemaon 18 Feb 2012 at 5:49 pm

    ChrisH,
    Thank you for taking the time to educate me.

    The Kirby article is written for the general public and is how people like me get information and form our opinions. I don’t have the wherewithal to analyze the legitimacy of the articles you’ve referenced, although I have just enough knowledge to comprehend the actual research. (that’s why when somebody places doubts on the legitimacy of an article published in one journal, i have to suspect similar shenanigans from others – or try to find out the sponsorship of each and every one and form my own opinions – not that interested!)

    Kirby is, of course, approaching the issue from an anecdotal viewpoint:

    “In many cases, parents report that the child had an abnormal reaction after being vaccinated (seizures, spiking-fevers, diarrhea, lethargy, high-pitched screaming and/or other symptoms).”

    and looking for answers from that viewpoint. When he finds something like Ratajczak’s article – it jives with what the parents in his circle are experiencing. And if he sees sponsorship of opposing conclusions may be motivated by financial, or other considerations, then he’s drawn to put together a larger viewpoint that the suspicion of vaccine-autism link has not been quelled.

    I don’t want to defend Ratajczak – truly, I’m not able. And I just got linked back to one of Dr. Novella’s earlier posts that calls Kirby a crank! ha ha ha ha ha! I guess perhaps Kirby goes too far in trying to influence conclusions. But without journalists like Kirby, would the public put pressure on agencies that have the resources to investigate? (I don’t know the answer to that question, i guess I’m just trying to defend journalism)

    But anyway, if I were a parent with a newborn, I would choose a conservative vaccine schedule, and I would do everything I could to ensure that my child’s immune system was as healthy as could be. I don’t see why parents are criticized for even taking the small step of delaying or spreading out vaccines – what’s wrong with that as long as they’re within a time frame to make them effective?
    (I’m not suggesting that you’ve been critical in that way, but others on this site have belittled cautious, but responsible parents – and that certainly doesn’t help resolve the issue of how to protect kids when parents are afraid of vaccine side-effects)

    Here are a couple more articles on the other “side” of this:

    Journal of Toxicology and Environmental Health, Part A: Current Issues
    Volume 74, Issue 14, 2011
    A Positive Association found between Autism Prevalence and Childhood Vaccination uptake across the U.S. Population
    http://www.tandfonline.com/doi/abs/10.1080/15287394.2011.573736

    Human & Experimental Toxicology
    Infant mortality rates regressed against number of vaccine doses routinely given: Is there a biochemical or synergistic toxicity?
    http://het.sagepub.com/content/early/2011/05/04/0960327111407644

    If you can make criticisms of those as well, I’d of course be interested to hear. But please don’t feel that you must take the time to do that.

    thanks again

  14. ChrisHon 18 Feb 2012 at 10:33 pm

    Mlema:

    But without journalists like Kirby, would the public put pressure on agencies that have the resources to investigate? (I don’t know the answer to that question, i guess I’m just trying to defend journalism)

    When was Kirby ever a journalist? Just link to any investigative reports he made before he was hired to write Evidence of Harm. Last I looked he wrote travel articles and sold them to newspapers. He also has a habit of cherry picking, just like Ratajczak.

    Gayle Delong is not a medical researcher, she is an economics professor. She assumed that every child who receives speech and language services in a school district is autistic. I am sure that would be a surprise to the hard of hearing friend of my daughter to learn that she now autistic. I once read that James Earl Jones used to stutter, is he also autistic? You can see her strange assumption discussed here (be sure to check out the links of other blogs that are mentioned that discussed that paper):

    Again, neither Miller nor Goldman are medical researchers. Mr. Miller claims to be a journalist, but has written several biased books on vaccines. And Mr. Goldman has a PhD in computer science from a diploma mill. The major issue with their paper is that they cherry picked which countries they were using, cherry picked data from one year and used creative counting techniques for the number of vaccines. Their Figure 1 is essentially a scatter plot that they forced a line on, it has no real meaning.

    Both papers are discussed extensively at the blog Respectful Insolence.

    What you have shown is that those who do not know how to do science write very bad papers. Especially if they are still persevering on thimerosal, which was removed from pediatric vaccines a decade ago. Gayle DeLong is on the board of SafeMinds, the same organization that could not find DTaP vaccines still with thimerosal eleven years ago:

    # Subject: Thimerosal DTaP Needed
    # From: Sally Bernard
    # Date: Wed, 27 Jun 2001 00:01:50 -0400
    # Yahoo! Message Number: 27456
    http://onibasu.com/archives/am/27456.html

    Hi all:

    A group of university-based researchers needs several vials of the older DTaP vaccine formulations which contained thimerosal for a legitimate research study. If anyone knows an MD who might have some of these vaccines or knows where to get them, please email me privately.

    Thank you.

    Sallie Bernard
    Executive Director
    Safe Minds

  15. Mlemaon 19 Feb 2012 at 12:26 am

    Wow! Unbelievable.
    Obviously you are much better informed that I am on this issue, and probably more than I ever will be. How can we hope to turn people’s minds away from these misconceptions regarding vaccines if scholarly journals continue to publish in this way? (Or should I be better able to tell which journals are “scholarly” – how do we sort these things out?) The questions are rhetorical, but I don’t expect them to really change anything in society’s perception. To the general public it’s very likely that “one bad apple spoils the whole bunch”.

    I think a lot of times people come in to a conversation between persons who already have common understanding (like the people on this site) and they get turned off because what the discussion addresses as established truth is not established with them, and they only sense a slightly derogatory tone towards “scientists” who hold an opposing view. They think the discussion is dismissive and insulting, when in reality it is exasperated with “pseudoscience”. They become offended, and that, in turn, cements their anti-vaxer position, which is, of course, counterproductive to advancing the goal of finding the causes of autism.

    I’m afraid people will continue to make their own conclusions based on what they and others in their communities (including online communities) continue to experience, which is apparently all coincidental. And with writers like Kirby on the job, those conclusions will be reinforced. It would be nice if persons such as yourself, who may be able to walk the sensible middle-ground as far as presenting evidence is concerned, could have a wider audience.

    If I had a national forum, I would encourage anti-vaxers to be more open-minded to the science, and I would encourage scientists to be patient with parents who are stretched to breaking. At least, with all the hubbub, there are more investigations into vaccine safety. And the mercury was removed. I don’t see that as a bad thing.

    I’m grateful i have the opportunity to access information here.
    Please accept my thanks for the replies you’ve written.

  16. ChrisHon 19 Feb 2012 at 12:46 pm

    You are welcome. Another good source of information is at another blog administered by Dr. Novella: http://www.sciencebasedmedicine.org/

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