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Updated: Jul 11, 2026
Long-term Behavioral and Reproductive Consequences of Embryonic Exposure to Low-dose Toxicants
Published on: March 6, 2018
Early thimerosal exposure and neuropsychological outcomes at 7 to 10 years
William W Thompson1, Cristofer Price, Barbara Goodson
1National Center for Immunizations and Respiratory Diseases, Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. wct2@cdc.gov
Insights
Early exposure to thimerosal (a mercury-containing preservative) in vaccines was not linked to neuropsychological deficits in children aged 7-10. This study found no causal association between thimerosal exposure and developmental outcomes.
Area of Science:
- Neuroscience
- Pediatric Health
- Toxicology
Background:
- Thimerosal, a mercury-based preservative in vaccines, has been hypothesized to cause neuropsychological deficits.
- Concerns exist regarding potential links between early thimerosal exposure and child neurodevelopment.
Purpose of the Study:
- To investigate the association between early thimerosal (mercury) exposure and neuropsychological functioning in children.
- To determine if mercury exposure from thimerosal-containing vaccines and immune globulins impacts neurodevelopmental outcomes.
Main Methods:
- 1047 children aged 7-10 underwent standardized neuropsychological testing (42 outcomes).
- Mercury exposure from thimerosal was quantified using immunization and medical records.
- Associations between mercury exposure (prenatal, neonatal, first 7 months) and neuropsychological performance were assessed.
Main Results:
- Few significant associations were found between thimerosal mercury exposure and 42 neuropsychological outcomes.
- Detected associations were small, with both positive and negative effects observed.
- Specific findings included links between prenatal mercury exposure and language/attention, and early childhood exposure with fine motor skills/attention.
Conclusions:
- The study does not support a causal link between early thimerosal exposure and neuropsychological deficits.
- No evidence suggests thimerosal in vaccines or immune globulins causes harm to neurodevelopmental functioning in children.
Background:
It has been hypothesized that early exposure to thimerosal, a mercury-containing preservative used in vaccines and immune globulin preparations, is associated with neuropsychological deficits in children.
Methods:
We enrolled 1047 children between the ages of 7 and 10 years and administered standardized tests assessing 42 neuropsychological outcomes. (We did not assess autism-spectrum disorders.) Exposure to mercury from thimerosal was determined from computerized immunization records, medical records, personal immunization records, and parent interviews. Information on potential confounding factors was obtained from the interviews and medical charts. We assessed the association between current neuropsychological performance and exposure to mercury during the prenatal period, the neonatal period (birth to 28 days), and the first 7 months of life.
Results:
Among the 42 neuropsychological outcomes, we detected only a few significant associations with exposure to mercury from thimerosal. The detected associations were small and almost equally divided between positive and negative effects. Higher prenatal mercury exposure was associated with better performance on one measure of language and poorer performance on one measure of attention and executive functioning. 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. 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.
Conclusions:
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.
