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Especially in connection with claims that thiomersal in vaccines is responsible for cases of autism, I've read that removing mercury through chelation can help autistic children.

Is there evidence that mercury plays any role in causing autism?

Is chelation therapy (e.g. using EDTA) effective in removing mercury from the body? And is it safe, or are there risks associated with it?

  • @phoog I'm using the international spelling, the US spelling is different. But they're both correct. – Mad Scientist Feb 10 '17 at 19:41
  • So I just noticed. I will delete my previous comment. I note that other posts on this site use thiomersal (thimerosal), so perhaps this question should follow that lead. – phoog Feb 10 '17 at 19:43
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Just looking at it logically, there are problems.

If we assume that mercury causes autism, then it should be very easy to locate "autism clusters" in areas with a high incidence of environmental mercury. This is not the case. Some clustering has been observed, but it correlated very closely with the education level of the parents (better educated parents were more likely to have a child diagnosed with an ASD).

The focus on mercury in thimerosal is completely disengenuous: there is far more mercury to be found in a can of tuna fish than in a vaccine made with thimerosal...The DTaP vaccine contained about 3 micrograms of mercury, while a 6 oz of tuna contains a little more than 52 micrograms (which is more than twice as much as the vaccines with the highest historical amount of thimerosal (Fluzone, and Afluria, both flu vaccines, neither of which contains it any longer)). Nearly all vaccines are thimerosal free now, and no corresponding decrease in autism has been reported.

Chelation therapy is commonly used for metal poisoning. There are known health effects and safety concerns which potentially include kidney failure and death.

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    @Oddthinking Yes, a matter of typing before thinking. The point is that you eat tuna fish and there are many things your body does to detoxify what is in your gut before you absorb it. Vaccines are typically injected directly into tissues, bypassing the body's first and best defense against pathogens: the skin; and also bypassing the second best: the gut. The point is that it is stupid to compare the mercury levels in something that you eat to the mercury levels in something that is injected. Also, never mind that many health professionals tell you to avoid tuna anyway because of the mercury. – fredsbend Jan 3 '14 at 8:08
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    @fredsbend From the Wikipedia article, one can infer that gastrointestinal lead absorption ranges between 15% and 50% over the course of a person's life, with younger people absorbing more lead. But even if we take the lower bound, eating 6 oz of tuna would cause the absorption of more than twice the amount of lead than the DTaP vaccine. – phoog Feb 8 '17 at 1:59
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    @fredsbend I am not certain why I confused lead and mercury, but I obviously did. The Wikipedia article on mercury poisoning says that the gastrointestinal absorption rate of metallic mercury is around 0.01%, but that the mercury in fish is largely methylmercury, which is "readily and completely absorbed by the gastrointestinal tract." This suggests that yes, a single 6-oz can of tuna actually introduces into the body about 17 times as much mercury as one dose of DTaP vaccine. – phoog Feb 10 '17 at 19:28
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    Since mercury has just about been eliminated from vaccines without a corresponding decrease in autism diagnoses it's pretty obvious it's not the cause. – Loren Pechtel Feb 11 '17 at 1:24
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TL;DR: There is some limited evidence of efficacy - especially if the patient also suffers heavy-metal poisoning - but it is rather weak.

[Note: This answer has had a substantial re-write, as I have now read the entire paper. Big props to Konrad Rudolph for finding me a copy.]

The following paper provides a systematic review for off-label and complementary and alternative medicine (CAM) treatments for Autism Spectrum Disorders (ASD):

Ann Clin Psychiatry. 2009 Oct-Dec;21(4):213-36. Novel and emerging treatments for autism spectrum disorders: a systematic review. Rossignol DA.

The author, Dr Daniel Rossignol, notes that there is only one FDA-approved treatment for autism (a treatment to lower irritability) and that, perhaps as a consequence, there is a high level of unapproved treatments being given to ASD children (as high as 74%), often without the knowledge of the child's medical doctors.

The story with chelation as a treatment is complex.

By some measures it is very successful:

In Table 1, titled "The top 20 complementary and alternative medicine treatments for children with an ASD, excluding diets", chelation ranks #1, with parents claiming an improvement in the child in 74% of 803 cases (based on tracking by the Autism Research Institute).

But... there are some big caveats.

I note that the ranking system - based on a survey of parental opinion - isn't very objective or reliable.

The author ranks the quality of the recommendation into grades, and gives the evidence for chelation a grade of C.

Here is how he chose the ranking:

Grade of recommendation

  • A At least one level 1a study or two level 1b studies
  • B At least one level 1b, 2a, or 3a study, or two level 2b or 3b studies
  • C At least one level 2b or 3b study, or two level 4 studies
  • D Level 5 evidence, or troublingly inconsistent or inconclusive studies of any level, or studies reporting no improvements
  • N No studies identified

To understand this, you need to understand the ranking of the underying studies:

Levels of Evidence

  • 1a Systematic Review (SR) or meta-analysis of RCTs with homogeneity or Cochrane review with favorable findings
  • 1b Prospective high-quality RCT
  • 2a SR of cohort (prospective, nonrandomized) studies with homogeneity
  • 2b Individual cohort (prospective, nonrandomized) study or low-quality RCT
  • 3a SR of case-control (retrospective) studies with homogeneity
  • 3b Individual case-control (retrospective) study
  • 4 Case series or reports
  • 5 Expert opinion without critical appraisal or based on physiology or bench research

[I've changed the table formatting to fit the StackExchange mark-up.]

So, we can see that while Level C is not to be simple dismissed, the best possible evidence it could include is an "Individual cohort (prospective, nonrandomized) study or low-quality RCT", which would not normally be considered enough evidence to recommend treatment under an Evidence-Based Medicine approach.


Delving deeper, the paper reviews well over a dozen different papers on chelation and autism.

Confusingly, several of them were on children who had both autism and heavy metal poisoning.

The studies sometimes gave apparently contradictory results, but given the low evidentiary quality of the studies (e.g. no control, small sample), this is to be expected.

The risks of chelation were briefly covered:

The reviewed studies of chelation in children with an ASD suggest that when properly administered, side effects of chelation are rare, idiosyncratic, and reversible.

However, the author noted two children in the USA (one with autism) have died from medication errors while receiving chelation.

The author concludes:

Overall, the collective strength of these studies investigating the use of chelation in individuals with an ASD is limited, as some are case reports and none included a control group. In some of these studies, it is unclear if the children had elevated heavy metal levels prior to initiating chelation or if this treatment directly caused the clinical improvements described. It is also possible that any improvements observed with chelation in these children could have been due to some chelator effect other than the removal of heavy metals because some chelators also remove pesticides, raise glutathione levels, and reduce oxidative stress. It should be noted that placebo-controlled studies of chelation in individuals with an ASD have not been performed; a large planned placebo-controlled study of chelation in children with autism was recently cancelled by the National Institute of Mental Health. However, despite the obvious limitations of the reviewed studies, their cumulative findings suggest that chelation might be a viable form of treatment in some individuals with an ASD who have elevated heavy metal burden, or as suggested by several studies, biochemical changes suggestive of metal toxicity. Further research investigating this possibility should thus be considered, including carefully designed controlled studies of chelation that include appropriate clinical monitoring as well as objective prescreening to identify children with ASD who have concomitant elevated heavy metal burden.

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Chelation has negative side effects, that can be fatal. In 2005, Tariq Nadama died from chelation treatment for autism, the third known death as a result of treatment by chelation to "cure" autism. The chemicals used for chelation are not without their own risks.

Furthermore, chelation as a treatment for mercury toxicity is only effective if applied very quickly and to stop the development of further symptoms. It does not reverse the symptoms already in place from mercury toxicity, so would not cure someone who was already diagnosed as autistic.

  • I've seen people recommending bentonite clay baths and one woman actually promoting eating diatomaceous earth (food grade, at least) as a means to 'detox' mercury and heavy metals in autistic kids. – Darwy Nov 18 '11 at 8:20
  • Ping: please reference. – Sklivvz May 5 '12 at 17:55
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    @Darwy: sure, and there's people promoting bicarbonate to cure cancer, that doesn't mean it actually works... – nico May 5 '12 at 18:41
  • Sorry Nico, I thought you could recognize my sarcasm. – Darwy May 5 '12 at 20:33
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    @Darwy: next time put a smiley... Internet is full of people who do actually say those things :) – nico May 6 '12 at 7:46

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