Preschool Blood Lead Level and Adolescent Substance Use: The Role of Language Competency

Background & Purpose: Elevated lead levels in children remain a persistent public health problem, particularly in urban, inner-city areas in the US. Although the adverse effects of early blood lead levels (BLL) on cognitive development and behavioral problems in children are well documented even with low BLL, few prospective studies have examined the association of childhood BLL with later adolescent outcomes such as substance use. This study examined the association between early BLL and adolescent substance use and whether childhood IQ, language skills, and/or externalizing behavior mediated the relationship, controlling for confounding biological (e.g., head circumference at birth) and environmental factors (e.g., maternal psychological distress and education, violence exposure, foster care).

Methods: This is a secondary analysis of a prospective cohort of prenatally substance-exposed children, primarily African-American, low socioeconomic status, recruited at birth. BLL were determined for 278 children at age 4, 265 (137 female, 128 male) of whom were assessed for IQ at age 11, language skills and externalizing behavior at age 12, and/or alcohol, tobacco, marijuana use and substance use problems at age 15. Children’s intelligence was assessed via the Wechsler Intelligence Scales for Children; language skills via the Test of Language Development-Intermediate; and externalizing behaviors via the Child Behavior Checklist. Biologic assays (hair, urine, bloodspots), along with self-report, were utilized to determine adolescent substance use. Substance use was specified as a latent variable (α = .72) with three indicators (alcohol, tobacco, and marijuana). Path analyses were conducted using the weighted least squares estimator with mean and variance adjustments.

Results: Children’s mean BLL at 4 years of age was 6.1 μg/dL (SD = 4.12; range 1.3 - 23.8). Approximately 31% of adolescents used tobacco or marijuana, 40% used alcohol, and 23% reported experiencing substance use related problems at age 15.7 (SD = 0.28). Preschool BLL had a direct effect on substance use (β = .16, p = .045) and an indirect effect on substance use problems via language skills (β = .049, 95% CI = .005 - .092, p = .027). Higher BLL at 4 years was related to lower language skills at age 12 (β = .15, p = .008) and, in turn, was related to substance use problems at 15 years (β = .32, p = .001). IQ was not related to substance use or substance use problems. Although no significant association between BLL and childhood externalizing behavior was found, externalizing behavior was related to substance use. Approximately 22% and 30% of the variation in substance use and substance use problems were accounted by the final model respectively, χ² (56) = 63.93, p = .22, CFI = .978, TLI = .968, RMSEA = .024 (90% CI = .000 - .049), WRMR = .12.

Conclusions: Elevated BLL in preschool years is a risk factor for adolescent substance use, raising additional attention to the detrimental effects of lead exposure on adolescent health. Early screening and intervention for language impairment may mitigate substance use and related health problems in urban, high-risk adolescents.