The Relationship between Hair Zinc and Lead Levels and Clinical Features of Attention-Deficit Hyperactivity Disorder

Abstract

Objectives : The goal of this study was to examine the association between zinc and lead level and symptoms of attention-deficit hyperactivity disorder (ADHD) among Korean children. Methods : A total of 89 clinic-referred children participated in the study (ADHD group=45, control group=44). The participants were 5-15 years old, and were mainly from urban areas of Seoul, Korea. ADHD was diagnosed using the Kiddie-Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version. We excluded children with a comorbid psychiatric disorder, medical illness requiring medication, or a prior history of taking ADHD medication. In order to evaluate the severity of ADHD symptoms, parents' Korean ADHD Rating Scale (K-ARS) was used. The ADHD diagnostic system (ADS) was used for evaluation of the severity of inattention and impulsivity. All participants completed the intelligence test and hair mineral analysis. Multiple regression analysis was used to examine the effect of hair zinc and lead levels on the K-ARS and ADS. We measured the predictive ability of the zinc and lead levels using logistic regression analysis. Results : The lead level explained the score for omission errors, commission errors, and response time SD in visual ADS in the ADHD group (adjusted <TEX>$R^2$</TEX>=.243, p<.01, adjusted <TEX>$R^2$</TEX>=.362, p<.01, and adjusted <TEX>$R^2$</TEX>=.275, p<.01), the score for omission errors of auditory ADS in ADHD group (adjusted <TEX>$R^2$</TEX>=.407, p<.01) and the entire group (adjusted <TEX>$R^2$</TEX>=.292, p<.01). Zinc was significantly explanatory for the K-ARS scores for the entire group (adjusted <TEX>$R^2$</TEX>=.248, p<.001) and the ADHD group (adjusted <TEX>$R^2$</TEX>=.247, p<.05). Conclusion : These findings suggest a possible role of zinc and lead in ADHD. Lead concentration in hair samples affected the ADS scores, and this was more prominent in children with ADHD. Children with ADHD had a lower zinc concentration in their hair, and the zinc concentration in hair showed negative correlation with the K-ARS score.