A systematic review of the association between lead levels in hair and urine in children with attention deficit hyperactivity disorder (ADHD)

Attention deficit hyperactivity disorder (ADHD), characterised by inattentiveness, hyperkinetic behaviour, and impulsivity in childhood, leads to decreased academic performance and learning in general. Among the environmental factors, lead (Pb) in the environment is considered a crucial public health issue associated with ADHD. This study assessed the existing literature for the association of hair and urine lead levels with ADHD. The studies included in this systematic review were case-control observational and prevalence studies of a place or population. For hair Pb levels, out of 478 participants, 89 were ADHD cases and 389 controls showed a pooled effect of a standardised mean difference of 0.30 (0.03–0.57). The overall effect Z was 2.16, which was statistically significant (P = 0.03). For urine Pb levels, there were 196 ADHD cases and 423 healthy controls. The pooled effect of the standardised mean difference was 0.34 (0.13–0.56). The overall effect Z was 3.12, which was statistically significant (P = 0.002). Pb estimations can reduce the disease burden of ADHD by non-invasive methods such as in hair and urine, which have better acceptance by parents.