Mercury Levels in Autism: Current Evidence
Mercury levels are not consistently elevated in patients with autism, and there is no established causal relationship between mercury exposure and autism spectrum disorder. 1, 2
Evidence on Mercury and Autism
The relationship between mercury and autism has been extensively studied with inconsistent findings:
The American Academy of Child and Adolescent Psychiatry practice parameter (2014) states that concerns about thimerosal (a mercury-containing preservative) causing autism have not been supported by the preponderance of available data 1.
A 2016 study found that people with autism actually had significantly less mercury in their locus ceruleus neurons (a brain region implicated in autism) compared to control subjects without autism 2.
A 2004 case-control study comparing hair and blood mercury levels between children with autism and neurotypical controls found no significant differences in mercury levels between the groups 3.
A 2007 meta-analysis concluded there is no evidence to support the association between mercury poisoning and autism (relative risk = 0.49,95%CI = 0.36-0.66) 4.
Conflicting Evidence
Some studies have suggested potential links between mercury and autism:
A 2020 review proposed that mercury exposure might induce immunologic changes in the brain indicative of autoimmune dysfunction, including the production of brain autoantibodies that may correlate with autism severity 5.
A 2014 study from Upper Egypt reported higher levels of mercury and lead in children with autism compared to controls, with improvement in symptoms following chelation therapy 6. However, this study has methodological limitations and contradicts findings from more rigorous research.
Environmental Exposures and Testing
Environmental Health Perspectives has identified several environmental chemicals that have been studied in relation to autism, including:
Air pollution, mercury, and pesticides are among the most frequently discussed environmental exposures 1.
Systematic reviews have noted limited evidence that developmental exposure to air pollutants may be associated with autism, but overall, there is insufficient evidence to establish strong associations between reviewed exposures and autism 1.
Clinical Implications
When evaluating patients with autism:
Mercury testing is not routinely recommended as part of the standard evaluation for autism spectrum disorder.
The diagnosis of autism should be based on validated diagnostic criteria and tools such as the Autism Diagnostic Interview-Revised (ADI-R) and Autism Diagnostic Observation Schedule (ADOS) 1.
There is insufficient evidence to support routine chelation therapy for autism management.
Risk Factors for Autism
The American Academy of Child and Adolescent Psychiatry identifies several established risk factors for autism spectrum disorder that are unrelated to mercury exposure:
- Genetic factors (high recurrence risk in siblings, higher concordance in identical twins)
- Closer spacing of pregnancies
- Advanced maternal or paternal age
- Extremely premature birth (<26 weeks' gestational age) 1
In conclusion, while some studies suggest potential associations between mercury and autism in certain contexts, the weight of evidence from higher-quality studies does not support mercury as a consistent biomarker or causal factor in autism spectrum disorder.