In Reply: Lead Exposure and Cognitive Outcomes of Children With Prenatal Cocaine Exposure

In Reply: Drs Greller and Hoffman have made a relevant point about lead exposure as a possible confounding variable affecting outcome in our longitudinal study of children exposed to cocaine. It is well known that lead is an important variable associated with the poverty status of our sample and the development of cognitive ability.¹ Although we did not collect data on lead exposure in our study, Nelson et al conducted a separate study² on our sample in which she assessed blood lead levels at 2 and 4 years. Although the entire sample was not included, there were totals of 143 children assessed at 2 years and 274 children at 4 years. At both time points, the prevalence of high blood lead level (≥10 mg/dL) was not different between the cocaine-exposed and nonexposed groups, nor were mean lead levels for the samples different. Therefore, lead exposure is unlikely to be a confounding variable for this cohort. Additionally, while lead levels independently predicted poorer performance and full scale IQs at 4 years and a lower Bayley Mental Development Index at 2 years, cocaine exposure was also an independent predictor of performance IQ in this subsample at 4 years.

The additive risk imposed from exposure to environmental toxins and nutritional deficiencies needs to be considered in outcome studies of high-risk children of low socioeconomic status and deserves further research as well as appropriate screening and interventional strategies for these populations.