A new study revealed that association between higher childhood blood lead levels and a greater risk for criminal behaviour (a dose-response relationship) in settings where blood lead levels are similar across low and high socioeconomic status was not clear.

Lead is a neurotoxin with well-documented effects on health. Research suggests that lead may be associated with criminal behaviour. The association is difficult to separate from low socioeconomic status, a factor in both lead exposure and criminal offending.

A higher childhood blood lead level (BLL) might be associated with greater risk of criminal conviction, recidivism (repeat conviction), a conviction for violent offences, and variety of self-reported criminal offending in a setting where BLL was not associated with low socioeconomic status.

To test the hypothesis the researchers involved 553 individuals in a prospective study based on a population-representative cohort born from New Zealand. The Dunedin Multidisciplinary Health and Development Study observed participants to age 38 years. Statistical analysis was performed. Blood lead level measured at age 11 years.

Official criminal conviction cumulative to age 38 years, single conviction or recidivism, a conviction for a nonviolent or violent crime, and self-reported variety of crime types at ages 15, 18, 21, 26, 32, and 38 years.The team found that the mean 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 offence conviction. Variety scores for self-reported offending ranged from 0 to 10 offence types at each assessment; higher numbers indicated greater crime involvement.

Self-reported offending followed the well-established age-crime curve. i.e., the mean variety of self-reported offending increased from 1.99 at age 15 years to its peak of 4.24 at age 18 years and 4.22 at age 21 years and declined thereafter to 1.10 at age 38 years.

Blood lead level was a poor discriminator between no conviction and conviction. 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.

The 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. The study results failed to support a dose-response association between BLL and consequential criminal offending. Responses toward lead exposure should focus on consequences for health, not potential consequences for crime, the team suggested.