Zinc in Autism: a Case-Control Study

Background: Zinc supplementation is sometimes advocated to manage autism despite a paucity of research evidence on this topic.  Zinc supplementation is purported to have some efficacy in managing hyperactivity symptoms in non autistic samples, and could therefore play a role in the management of hyperactivity in autism, which is notoriously difficult. 

Objectives: 1) To evaluate if young children recently diagnosed with autism or any other PDD have lower zinc levels compared to pediatric controls; and 2) to identify, within the autism sample, potential clinical correlates of zinc levels. 

Methods: The study was organized in the Autism Disorder Program of the McGill University Montreal Children’s Hospital; 70 children with PDD were recruited near the time of initial diagnosis and matched on age and sex to 76 pediatric controls who were all negative on an autism screening questionnaire. PDD children were evaluated with the ADI-R, the ADOS, an expert clinical evaluation, the Vineland Adaptive Behavior scales, and the Aberrant Behavior Checklist. For both groups, blood and hair samples were obtained and analyzed for zinc content using inductively coupled plasma mass spectrometry (ICP-MS) in a state-of-the art toxicology laboratory of Quebec.

Results: Cases and controls were similar with respect to age (50.3 vs 47.9 months;NS), sex (% male 88.6 vs 80.3; NS), and familial socio-demographic characteristics (family income, mother’s education and ethnicity, number of siblings and birth rank, and marital status). No statistical difference between cases and controls was found for zinc levels in the blood (187.4 vs 183.3 μmol/L; NS) and in the hair (137.1 vs 143.2 μg/g; NS). Within the PDD group, parametric and non-parametric correlations between blood and hair levels of zinc were all not significant for the Social, Non-verbal communication, Repetitive behaviour scores of the ADI-R (range for r’s: -0.11-0.04; all NS), for the Communication, Social Interaction and total scores of the ADOS-G (range for r’s: -0.16-0.07; all NS), and for the 5 standardized scores of the Vineland scales (Communication, Socialization, Daily Living Skills, Motor skills, and ABC composite) (range for r’s: -0.17-0.22; all NS). For the 51 PDD children with an ABC available, no significant correlation was found between the ABC Hyperactivity subscale and zinc blood (r=-.12; NS) and hair (r=-.14; NS) levels. Correlations for the 4 other ABC subscales and the total ABC score were equally non significant. Conclusions: There is no evidence that zinc levels are lower in young children recently diagnosed with PDD compared to pediatric controls, nor that zinc levels predict levels of functioning or autistic symptomatology in children with PDD. Furthermore, there is no evidence that hyperactivity symptoms in young children with PDD are correlated with zinc levels.  Zinc supplementation is therefore not recommended as part of the routine medical management of autism.