Association of Childhood Blood Lead Levels With Criminal Offending.

Importance: Lead is a neurotoxin with well-documented effects on health. Research suggests that lead may be associated with criminal behavior. This association is difficult to disentangle from low socioeconomic status, a factor in both lead exposure and criminal offending.
Objective: To test the hypothesis that a higher childhood blood lead level (BLL) is associated with greater risk of criminal conviction, recidivism (repeat conviction), conviction for violent offenses, and variety of self-reported criminal offending in a setting where BLL was not associated with low socioeconomic status.
Design, Setting, and Participants: A total of 553 individuals participated in a prospective study based on a population-representative cohort born between April 1, 1972, and March 31, 1973, from New Zealand; the Dunedin Multidisciplinary Health and Development Study observed participants to age 38 years (December 2012). Statistical analysis was performed from November 10, 2016, to September 5, 2017.
Exposures: Blood lead level measured at age 11 years.
Main Outcomes and Measures: Official criminal conviction cumulative to age 38 years (data collected in 2013), single conviction or recidivism, conviction for nonviolent or violent crime, and self-reported variety of crime types at ages 15, 18, 21, 26, 32, and 38 years.
Results: Participants included 553 individuals (255 female and 298 male participants) who had their blood tested for lead at age 11 years. The mean (SD) BLL at age 11 years was 11.01 (4.62) μg/dL. A total of 154 participants (27.8%) had a criminal conviction, 86 (15.6%) had recidivated, and 53 (9.6%) had a violent offense conviction. Variety scores for self-reported offending ranged from 0 to 10 offense types at each assessment; higher numbers indicated greater crime involvement. Self-reported offending followed the well-established age-crime curve (ie, the mean [SD] variety of self-reported offending increased from 1.99 [2.82] at age 15 years to its peak of 4.24 [3.15] at age 18 years and 4.22 [3.02] at age 21 years and declined thereafter to 1.10 [1.59] at age 38 years). Blood lead level was a poor discriminator between no conviction and conviction (area under the curve, 0.58). Overall, associations between BLL and conviction outcomes were weak. The estimated effect of BLL was lower for recidivism than for single convictions and lower for violent offending than for nonviolent offending. Sex-adjusted associations between BLL reached statistical significance for only 1 of the 6 self-reported offending outcomes at age 15 years (r = 0.10; 95% CI, 0.01-0.18; P = .02).
Conclusions and Relevance: This study overcomes past limitations of studies of BLL and crime by studying the association in a place and time where the correlation was not confounded by childhood socioeconomic status. Findings failed to support a dose-response association between BLL and consequential criminal offending.