Seafood Consumption and Blood Mercury Concentrations in Jamaican Children with and without Autism Spectrum Disorders

Background:

Mercury is a toxic metal with harmful effects on human health that could lead to neurodevelopmental disorders including language, learning, and attention deficits as well as intellectual and developmental disabilities. Autism Spectrum Disorders (ASDs) are lifelong neurodevelopmental and behavioral disorders that manifest in early childhood and are characterized by impairments and difficulty in social interaction, communication and language as well as repetitive behavior and sensory–motor movements. The etiology of ASD is complex and not fully understood. Several studies have investigated the possible association between exposure to mercury and ASD but their findings are conflicting.

Objectives: To investigate the association between blood mercury concentrations and ASD in children, and to assess the role of fish consumption in blood mercury concentrations in Jamaican children.

Methods: The Jamaican Autism study is a NIH-supported age- and sex-matched case-control study that began enrollment in December 2009, investigating whether environmental exposures to mercury, lead, arsenic, manganese, and cadmium have a role in the onset of autism. We administered the Autism Diagnostic Observation Schedule (ADOS) and the Autism Diagnostic Interview-Revised (ADI-R) to children, 2-8 years of age, in the University of West Indies’ Jamaica Autism Database, who were previously identified as being at risk for ASD based on the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) criteria and the Childhood Autism Rating Scale.  For each case, we identified an age- and sex-matched control using the Social Communication Questionnaire. We also administered a pre-tested questionnaire to assess demographic and socioeconomic information, parental education levels, medication, childhood immunization history, and potential exposure to mercury through food, with a particular focus on the types and amount of seafood consumed by children. At the end of the interview, we collected 2 mLs of whole blood from each child, to be analyzed in the US for a variety of environmental exposures. Using General Linear Models we compared mean blood mercury concentrations by ASD status for the available 65 matched pairs who had all the required data.

Results: In our sample, 86.2% of children were male with a mean age of about 65 months. The cases and controls were 96.9% and 98.5% Afro-Caribbean, respectively. We found a significant upward trend for the mean blood mercury concentrations in relation to the frequency of seafood consumption for both cases and controls (P-values < 0.05). Children who ate “sardine or mackerel fish” had a significantly higher geometric mean blood mercury concentration than children who did not eat these fish (0.96 μg/L vs 0.41 μg/L, P-value = 0.0028). After controlling for parental education levels, maternal age, and frequency of seafood consumption, there was no significant association between blood mercury concentrations and ASD status. 

Conclusions: We did not find a significant association between ASD and blood mercury concentrations. However, we recommend development of appropriate interventions to increase parents’ awareness that excessive seafood consumption can lead to elevated mercury blood concentrations in children and is potentially hazardous to human health.