In our report of cognitive effects of iron deficiency in infancy depending on socioeconomic status (SES),1 we emphasized that iron deficiency is not the only developmental risk associated with low SES. Dr Petrone's letter draws attention to another important risk factor: elevated lead levels. They are associated with both low SES and iron deficiency and thus might further compromise development. We received related comments about other concomitants of low SES. John F. DiTragilia, MD, inferred from our paper that “low SES is much more important than Fe [iron] deficiency in depressing cognitive scores” (e-mail correspondence, November 2006). Greg Duncan, PhD, Edwina S. Tarry Professor of Human Development and Social Policy at Northwestern University, pointed out that SES effects on child development often disappear when maternal IQ is taken into account (personal communication, November 2006). Because data on maternal IQ and infant blood lead levels were available for the Costa Rica sample, we addressed these issues in further analyses.
Lozoff B, Jimenez E, Smith JB. Iron Deficiency, Lead Poisoning, and Development—Reply. Arch Pediatr Adolesc Med. 2007;161(5):523-524. doi:10.1001/archpedi.161.5.523-b