Regarding “Persistent Organochlorine Compounds and Birth Weight”

LETTER Regarding “Persistent Organochlorine Compounds and Birth Weight” Dear Editors: We read with great interest the article, “Persistent Organochlorine Compounds and Birth Weight”, published in the March 2003 issue of the Annals of Epidemiology (1). Gladen et al. conclude that “prenatal exposure to the chemicals studied, at concentrations currently seen in this population, does not impact weight at birth”. We found a problem in their analytical approach. A re-analysis may yield a different conclusion. The authors showed that polychlorinated biphenyls (PCBs) may decrease and dichloro-diphenyl-ethylene (DDE) may increase birth weight. For instance, the reduction of birth weight with increasing PCB #187 concentrations was: lower to upper tertile: 3469 to 3451 to 3379 g; for p,p’-DDE: lower to upper tertile: 3329 to 3483 to 3488 g. However, both effects were not statistically significant. PCB has been reported in previous studies to be associated with reduced birth weight (2, 3). DDE is suspected to exert an estrogenic effect (4, 5); and maternal estrogens during pregnancy have been shown to increase birth weight (6). We were surprised to realize that the authors did not assess the effect of PCB and DDE simultaneously in their statistical analyses. It is known that due to their bioaccumulation and persistence both PCBs and DDE occur together. In children and adults, the rank correlation between DDE and PCBs is 0.6 and higher (7–9). Since both organochlorines are correlated and may have antipodal effects on birth weight, it is particularly important to include both in statistical models that attempt to assess their effects. Hence, we need to understand what effects both PCBs and DDE were having, taking into consideration their counterbalancing effect in one statistical model. The assessment provided

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by the authors may change, if one of the two contaminants gains a stronger association and/or statistical significance. Wilfried Karmaus, MD, MPH Xiaobei Zhu, MD Department of Epidemiology Michigan State University East Lansing, MI, USA

REFERENCES 1. Gladen BC, Shkiryak-Nyzhnyk ZA, Chyslovska N, Zadorozhnaja TD, Little RE. Persistent organochlorine compounds and birth weight. Ann Epidemiol. 2003;13:151–157. 2. Taylor PR, Lawrence CE, Hwang HL, Paulson AS. Polychlorinated biphenyls: Influence on birthweight and gestation. Am J Public Health. 1984; 74:1153–1154. 3. Patandin S, Koopman-Esseboom C, de Ridder MA, Weisglas-Kuperus N, Sauer PJ. Effects of environmental exposure to polychlorinated biphenyls and dioxins on birth size and growth in Dutch children. Pediatr Res. 1998;44:538–545. 4. Sonnenschein C, Soto AM. An updated review of environmental estrogen and androgen mimics and antagonists. J Steroid Biochem Mol Biol. 1998; 65:143–150. 5. You L, Sar M, Bartolucci E, Ploch S, Whitt M. Induction of hepatic aromatase by p, p’-DDE in adult male rats. Mol Cell Endocrinol. 2001;178:207–214. 6. Kaijser M, Granath F, Jacobsen G, Cnattingius S, Ekbom A. Maternal pregnancy estriol levels in relation to anamnestic and fetal anthropometric data. Epidemiology. 2000;11:315–319. 7. Covaci A, de Boer J, Ryan JJ, Voorspoels S, Schepens P. Distribution of organobrominated and organochlorinated contaminants in Belgian human adipose tissue. Environ Res. 2002;88:210–218. 8. Karmaus W, Huang S, Cameron L. Parental concentration of dichlorodiphenyl dichloroethene and polychlorinated biphenyls in Michigan fish eaters and sex ratio in offspring. J Occup Environ Med. 2002;44:8–13. 9. Karmaus W, DeKoning EP, Kruse H, Witten J, Osius N. Early childhood determinants of organochlorine concentrations in school-aged children. Pediatr Res. 2001;50:331–336.

1047-2797/04/$–see front matter doi:10.1016/j.annepidem.2003.08.007