Lead and Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms: a meta-analysis.

This meta-analysis examined the association between Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms and lead exposure in children and adolescents. Thirty-three studies published between 1972 and 2010 involving 10,232 children and adolescents were included. There was a small to medium association between inattention symptoms and lead exposure (r=.16, k=27, p<.001) and a similar association between hyperactivity/impulsivity symptoms and lead exposure (r=.13, k=23, p<.001). There was significant heterogeneity among the effect sizes for both inattention symptoms and for hyperactivity/impulsivity symptoms, with studies using hair analysis to assess lead burden yielding substantially larger effect sizes than those using other methods. Excluding the hair analysis studies, the average rs were .14 for inattention (k=23, p<.001) and .12 for hyperactivity/impulsivity (k=21, p<.001). Overall, the relation between lead exposure and ADHD symptoms was similar in magnitude to the relation between lead exposure and decreased IQ and between lead exposure and conduct problems.