Blood mercury concentrations in CHARGE Study children with and without autism

Abstract

Background: Some authors have reported higher blood mercury (Hg) levels in persons with autism, relative to unaffected controls.

Objectives: We compared blood total Hg concentrations in children with autism or autism spectrum disorder (AU/ASD) and typically developing (TD) controls in population-based samples, and determined the role of fish consumption in differences observed.

Methods: The Childhood Autism Risk from Genetics and the Environment (CHARGE) Study enrolled children 2-5 years of age. After diagnostic evaluation, we analyzed three groups: AU/ASD, non-AU/ASD with developmental delay (DD), and population-based TD controls. Mothers were interviewed about household, medical, and dietary exposures. Blood Hg was measured by inductively coupled plasma mass spectrometry. Multiple linear regression analysis was conducted (n = 452) to predict blood Hg from diagnostic status controlling for Hg sources.

Results: Fish consumption strongly predicted total Hg concentration. AU/ASD children ate less fish. After adjustment for fish and other Hg sources, blood Hg levels in AU/ASD children were similar to those of TD children (p = 0.75); this was also true among non-fish eaters (p = 0.73). The direct effect of AU/ASD diagnosis on blood Hg not through the indirect pathway of altered fish consumption was a 12% reduction. DD children had lower blood Hg concentrations in all analyses. Dental amalgams in children with gum-chewing or teeth-grinding habits predicted higher levels.

Conclusions: After accounting for dietary and other differences in Hg exposures, total Hg in blood was neither elevated nor reduced in CHARGE Study preschoolers with AU/ASD compared with unaffected controls, and resembled those of nationally representative samples.

Figure 1

Directed acyclic graph (DAG) for models 0 (A), 1 (B), and 2 (C). Each arrow represents a cause-and-effect relationship: solid arrows, associations that are established, with heavier arrows indicating stronger associations; dotted arrows, speculative or weaker associations (e.g., without a priori evidence). Boxes labeled U-1, U-2, and U-3 in (B) represent hypothesized unmeasured confounders. The association we studied between autism diagnosis (Dx) and blood Hg concentration is represented with a question mark. Thimerosal-containing vaccines were omitted because of the small number exposed within the relevant time frame, but in each model in these DAGs this factor would have appeared identically as other Hg sources. For further explanation of these models, see “Materials and Methods.”

Figure 2

Distribution of the natural logarithm of total Hg concentrations in blood from children participating in the CHARGE study, 2003–2006 (n = 566), by diagnostic group: TD, AU/ASD, and DD.