A systematic literature review on the association between exposures to toxic elements and an autism spectrum disorder.

This large review looked at whether exposure to toxic metals like lead, mercury, and arsenic is linked to autism. Researchers combined results from 40 studies comparing metal levels in autistic children versus typical children. They found higher levels of some metals in blood and urine samples from autistic children, but results varied depending on which body sample was tested. The findings suggest toxic metals might play a role in autism development, but more research is needed to understand this relationship.

This systematic review and meta-analysis examined the relationship between toxic metal exposure and autism spectrum disorder by analyzing 40 studies from 1982-2022. The research investigated five toxic metals (mercury, lead, cadmium, arsenic, aluminum) in blood, hair, and urine samples from autistic individuals compared to healthy controls. Results showed significantly higher levels of lead and mercury in blood, lead in hair, arsenic in urine, and aluminum in urine among autistic individuals. However, findings varied by sample type and metal, with some showing lower levels in autistic individuals.

The analysis suggests toxic metals may be environmental factors in ASD development, though the relationship is complex and varies by exposure biomarker.

While this meta-analysis suggests associations between certain toxic metal exposures and autism, the varied findings across sample types indicate complexity in this relationship. Clinicians should be aware of potential environmental factors but avoid overinterpreting these associations as causal. Further research with standardized measurement approaches is needed before clinical recommendations can be made.

The abstract does not specify individual study quality, sample sizes, or methodological details of included studies. Variations in results across sample types suggest measurement inconsistencies. Causal relationships cannot be established from this observational data, and confounding factors are not discussed.

Autism spectrum disorder (ASD) is a neurodevelopmental illness characterized by difficulties in social communication and repetitive behaviors. There have been many previous studies of toxic metals in ASD. Therefore, the priority of this study is to review the relationships between exposure to toxic metals and ASD. This study was based on a comprehensive search of international databases, such as Web of Science, Science Direct, Scopus, PubMed, and Google Scholar, for all works related to the subject under discussion from 1982 to 2022.

We further summarize published data linked to this topic and discuss with clarifying evidence that agrees and conflicts with the association between exposure to toxic metals, including mercury (Hg), lead (Pb), cadmium (Cd), arsenic (As), and aluminum (Al) and ASD. 40 out of 63 papers met the requirements for meta-analysis. Blood Pb levels (standardized mean difference (SMD) = 0.81; 95 % confidence interval (CI): 0.36-1.25), blood Hg (SMD = 0.90; CI: 0.30-1.49), hair Pb (SMD = 1.47; CI: 0.03-2.92), urine As (SMD = 0.65; CI: 0.22-1.09), and urine Al levels (SMD = 0.85; CI: 0.40-1.29) in autistic individuals were significantly higher than those of healthy control (HC). Whereas, blood As levels (SMD = 1.33; CI: -1.32-3.97), hair As (SMD = 0.55; CI: -0.14-1.24), hair Cd (SMD = 0.60; CI: -0.31-1.51), hair Hg (SMD = 0.41; CI: -0.30-1.12), hair Al (SMD = 0.87; CI: -0.02-1.77), urine Pb (SMD = -0.68; CI: -2.55-1.20), urine Cd (SMD = -0.26; CI: -0.94-0.41), and urine Hg levels (SMD = 0.47; CI: -0.09-1.04) in autistic individuals were significantly lower than those of HC. Toxic metal content significantly differed between individuals with ASD and HC in the current meta-analysis.

The results assist in clarifying the significance of toxic metals as environmental factors in the development of ASD.