Study shows neighborhood poverty and lead exposure cause loss of cognition in young children

In this article, authors Wodtke et al. investigate how living in a disadvantaged neighborhood from birth until entering school negatively affects children’s vocabulary skills, and they conclude that lead contamination can act as a causal mechanism to explain it. They found that beyond the characteristics of families and individuals, children’s neighborhoods shape their exposure to environmental toxins like lead, which in turn affect their cognition. Their paper outlines a theoretical model of neighborhood effects on cognitive development during early childhood, which highlights the mediating role of exposure to neurotoxic lead.

To test the model, the authors combined information from three sources that focus on Chicago, a city with concentrated poverty, racial segregation, and known lead hazards, for which there is good data available on both cognition and lead exposure during early childhood. First, they made use of longitudinal data collected about children in Chicago in the Project on Human Development in Chicago Neighborhoods (PHDCN), available from the National Archive of Criminal Justice Data (NACJD). The PHDCN was a large-scale, interdisciplinary study of how families, schools, and neighborhoods affect child and adolescent development. One component of the PHDCN was the Longitudinal Cohort Study, which was a series of coordinated longitudinal studies that followed over 6,000 randomly selected children, adolescents, and young adults in seven age-groups, including a birth cohort under 1 year of age at baseline, and their primary caregivers. They were surveyed in three waves between 1994 and 2002, to examine the changing circumstances of their lives, as well as the personal characteristics that might lead them toward or away from a variety of antisocial behaviors. Numerous measures were administered to respondents to gauge various aspects of human development, including individual differences, as well as family, peer, and school influences. To test their model, Wodtke et al. analyzed a sample of 1,266 children from the birth cohort through school entry. They used two other sources of data in conjunction with PHDCN data. To measure areal risk of lead exposure, they used the Chicago Department of Public Health (CDPH) blood-lead surveillance database, and to measure neighborhoods’ socioeconomic composition over time they used the GeoLytics Neighborhood Change Database. The Peabody Picture Vocabulary Test that was administered in the third wave of the PHDCN was used to measure cognitive ability. The authors also controlled for several covariates measured at baseline, ranging from each child’s race to the education level of their primary caregiver.

The authors note that, “Short of conducting a sequentially randomized field experiment, [their] analysis provides some of the more credible evidence that neighborhood disadvantage causally affects cognitive development.” The PHDCN data collected 20 years ago show that in many Chicago neighborhoods, a majority of resident children had elevated levels of lead in their blood. The data also showed that disadvantaged and lead-contaminated neighborhoods were spatially concentrated on Chicago’s South and West Sides, which are predominantly populated with racial minorities who suffer from high rates of poverty. Even though lead levels in Chicago residents began to drop after 2010, due in large part to prevention and remediation programs, the authors emphasize that “contemporary cohorts of children in disadvantaged neighborhoods remain at greater risk of lead exposure in many American cities, and even at the lower doses that are now more common, lead can harm their developing brains.” Further, lead is only one of the many neurotoxins prevalent in poor communities. This study provides “considerable evidence that growing up in a disadvantaged neighborhood inhibits cognitive development because these environments are literally toxic for children.”