Lead exposure and risk of ADHD and conduct disorders in children: evidence from a retrospective cohort in Philadelphia, PA

Childhood lead exposure remains a significant public health concern, particularly in urban settings with persistent socioeconomic disadvantage. Although prior studies have linked lead exposure to adverse neurodevelopmental outcomes, evidence using clinically diagnosed neurobehavioral disorders at contemporary low blood lead levels (BLLs) is limited. We conducted a retrospective cohort study of children aged 11 years or younger who received care through the Temple University Health System in Philadelphia, Pennsylvania, between 2010 and 2020. BLLs were obtained from electronic health records and analyzed as continuous measures and dichotomized at 3.5 µg/dL. Attention-deficit/hyperactivity disorder (ADHD) and conduct disorders were identified using international classification diagnoses (ICD) codes, and only incident diagnoses occurring after blood lead measurement were considered. Multivariable logistic regression models were fit adjusted for individual- and neighborhood-level sociodemographic factors selected using a directed acyclic graph framework. Sex-stratified analyses were conducted to assess effect modification. Among 13,989 children included in the ADHD analysis, 751 (5.4%) were diagnosed with ADHD. Among 14,098 children included in the conduct disorder analysis, 247 (1.8%) were diagnosed with a conduct disorder. Higher log 10 -transformed continuous BLLs were associated with increased odds of ADHD diagnosis (adjusted OR 1.51; 95% CI 1.37, 1.67). Children with BLLs ≥ 3.5 µg/dL had higher odds of ADHD (adjusted OR 1.84; 95% CI 1.56, 2.16) compared with those with BLLs < 3.5 µg/dL, with stronger associations observed among males than females. Associations between log 10 -transformed continuous BLLs and conduct disorders were positive but not statistically significant (adjusted OR 1.12; 95% CI 0.95, 1.31), and no sex-specific associations were observed. Childhood lead exposure was associated with increased risk of ADHD in this urban clinical population, including at blood lead levels at or above the current reference value set by the Centers for Disease Control and Prevention, emphasizing the importance of continued prevention efforts. These findings underscore the ongoing neurodevelopmental risks of low-level lead exposure and highlight the disproportionate burden placed on children residing in socioeconomically disadvantaged urban communities.