Breast-feeding and Child Lead Exposure: A Cause for Concern

Abstract

See related article, p 663It would be difficult to overstate the benefits that breast-feeding provides to infants, mothers, families, and society. Included are benefits to overall child health, nutrition, immunologic function, development, and psychological adjustment.1Gartner L.M. Morton J. Lawrence R.A. Naylor A.J. O'Hare D. Schanler R.J. et al.American Academy of Pediatrics Section on Breastfeeding. Breastfeeding and the use of human milk.Pediatrics. 2005; 115: 496-506Crossref PubMed Scopus (2159) Google Scholar There are relatively few absolute contraindications to breast-feeding. They include infants with galactosemia and mothers with active untreated tuberculosis or who are positive for human T-cell lymphotropic virus type I or type II, those receiving radioisotopes or who have had exposure to radioactive materials, those who are receiving antimetabolites or certain other chemotherapeutic agents or using drugs of abuse, and mothers with herpes simplex lesions on a breast (although infants may feed from the other breast if clear of lesions).1Gartner L.M. Morton J. Lawrence R.A. Naylor A.J. O'Hare D. Schanler R.J. et al.American Academy of Pediatrics Section on Breastfeeding. Breastfeeding and the use of human milk.Pediatrics. 2005; 115: 496-506Crossref PubMed Scopus (2159) Google Scholar Maternal HIV infection is a contraindication to breast-feeding in the United States2Read J. Human milk, breastfeeding, and transmission of human immunodeficiency virus type 1 in the United States.Pediatrics. 2003; 112: 1196-1205Crossref PubMed Scopus (70) Google Scholar but not necessarily so in developing countries.3HIV and Infant FeedingA Guide for Health Care Managers and Supervisors. World Health Organization, Geneva, Switzerland2004Google Scholar In all other situations, decisions about breast-feeding must be made on an individual basis, weighing the potential risks to the infant or mother versus the remarkable number of substantial benefits of breast-feeding.4Lawrence R. A Review of the Medical Benefits and Contraindications to Breastfeeding in the United States (Maternal and Child Health Technical Information Bulletin). National Center for Education in Maternal and Child Health, Arlington, VA1997Google Scholar See related article, p 663 In this issue of The Journal, Lozoff et al report data from 3 countries (Costa Rica, Chile, and the United States, or more specifically, Detroit, Michigan), in 3 different decades, in settings that differed in infant blood lead levels, environmental lead sources, and breast-feeding patterns, all showing higher infant blood lead concentrations associated with longer breast-feeding duration.5Lozoff B. Jimenez E. Wolf A. Angelilli M. Zatakia J. Jacobson S. et al.Higher infant blood lead levels with longer duration of breastfeeding.J Pediatr. 2009; 155: 663-667Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar This was true for exclusive breast-feeding and for total duration of breast-feeding in each of the countries studied. These findings, as the authors point out, in no way obviate the many benefits of breast-feeding or suggest that breast-feeding be contraindicated, but they do raise a number of important concerns and questions. Lead remains one of the most common of all childhood toxic environmental exposures. Even though mean blood lead levels of children in the United States have declined precipitously in the past 2 decades and our knowledge of the pathways by which children are exposed has grown impressively (and this article now highlights that breast milk can serve as still another source), so has our knowledge of untoward neurocognitive effects at blood lead levels once believed to be quite safe. In fact, the most recent Statement on the Prevention of Childhood Lead Poisoning by the Centers for Disease Control and Prevention states that there is no known level of childhood lead that can be considered safe,6Preventing Lead Poisoning in Young Children Centers for Disease Control and Prevention, US Department of Health and Human Services, Atlanta, GA2005Google Scholar and analyses of cross-sectional secondary data,7Lanphear B. Dietrich K. Auinger P. Cox C. Cognitive deficits associated with blood lead concentrations <10 μg/dL in US children and adolescents.Public Health Rep. 2000; 115: 521-529Crossref PubMed Scopus (698) Google Scholar prospectively collected primary data,8Canfield R.L. Henderson Jr., C.R. Cory-Slechta D.A. Cox C. Jusko T.A. Lanphear B.P. Intellectual impairment in children with blood lead concentrations below 10 μg per deciliter.N Engl J Med. 2003; 348: 1517-1526Crossref PubMed Scopus (1640) Google Scholar a systematic review of the literature,6Preventing Lead Poisoning in Young Children Centers for Disease Control and Prevention, US Department of Health and Human Services, Atlanta, GA2005Google Scholar and meta-analyses of pooled data from 7 international studies9Lanphear B.P. Hornung R. Khoury J. Yolton K. Baghurst P. Bellinger D.C. et al.Low-level environmental lead exposure and children's intellectual function: an international pooled analysis.Environmen Health Perspect. 2005; 113: 894-899Crossref PubMed Scopus (1530) Google Scholar all show decreases of children's IQ associated with increasing blood lead levels below 10 μg/dL, and all indicate that at levels below 10 μg/dL, there is a greater decrease in child IQ associated with increasing blood lead levels than at levels above 10 μg/dL. In addition, findings suggest that lead exposure during the first months of life have adverse effects on weight gain of healthy, breast-fed infants and that both maternal lead burden and child blood lead levels are negatively associated with postnatal weight gain.10Sanin L.H. Gonzalez-Cossio T. Romieu I. Peterson K.E. Ruiz S. Palazuelos E. et al.Effect of maternal lead burden on infant weight and weight gain at one month of age among breastfed infants.Pediatrics. 2001; 107: 1016-1023Crossref PubMed Scopus (64) Google Scholar Although the findings in the article by Lozoff et al are concerning, they are neither unexpected nor inconsistent with what is already known about the effects of pregnancy and lactation on maternal lead metabolism and the transmission of lead from breast milk to nursing infants. Research consistently demonstrates that nursing infants may be exposed to lead from breast milk. Maternal serum and breast milk lead levels as well as maternal bone lead stores have all been shown to be correlated with infant blood lead levels.10Sanin L.H. Gonzalez-Cossio T. Romieu I. Peterson K.E. Ruiz S. Palazuelos E. et al.Effect of maternal lead burden on infant weight and weight gain at one month of age among breastfed infants.Pediatrics. 2001; 107: 1016-1023Crossref PubMed Scopus (64) Google Scholar, 11Ettinger A. Tellez-Rojo M. Amarasiriwardena C. Bellinger D. Peterson K. Schwartz J. et al.Effect of breast milk lead on infant blood lead levels at 1 month of age.Environ Health Perspect. 2004; 112: 1381-1385Crossref PubMed Scopus (63) Google Scholar Lead from both current maternal exposure and that accumulated in bone from prior exposure are available to the nursing infant via breast milk. Infant blood lead levels at 1 month of age are significantly correlated with umbilical cord10Sanin L.H. Gonzalez-Cossio T. Romieu I. Peterson K.E. Ruiz S. Palazuelos E. et al.Effect of maternal lead burden on infant weight and weight gain at one month of age among breastfed infants.Pediatrics. 2001; 107: 1016-1023Crossref PubMed Scopus (64) Google Scholar, 11Ettinger A. Tellez-Rojo M. Amarasiriwardena C. Bellinger D. Peterson K. Schwartz J. et al.Effect of breast milk lead on infant blood lead levels at 1 month of age.Environ Health Perspect. 2004; 112: 1381-1385Crossref PubMed Scopus (63) Google Scholar and maternal blood11Ettinger A. Tellez-Rojo M. Amarasiriwardena C. Bellinger D. Peterson K. Schwartz J. et al.Effect of breast milk lead on infant blood lead levels at 1 month of age.Environ Health Perspect. 2004; 112: 1381-1385Crossref PubMed Scopus (63) Google Scholar lead at delivery and with maternal blood,10Sanin L.H. Gonzalez-Cossio T. Romieu I. Peterson K.E. Ruiz S. Palazuelos E. et al.Effect of maternal lead burden on infant weight and weight gain at one month of age among breastfed infants.Pediatrics. 2001; 107: 1016-1023Crossref PubMed Scopus (64) Google Scholar, 11Ettinger A. Tellez-Rojo M. Amarasiriwardena C. Bellinger D. Peterson K. Schwartz J. et al.Effect of breast milk lead on infant blood lead levels at 1 month of age.Environ Health Perspect. 2004; 112: 1381-1385Crossref PubMed Scopus (63) Google Scholar patella,10Sanin L.H. Gonzalez-Cossio T. Romieu I. Peterson K.E. Ruiz S. Palazuelos E. et al.Effect of maternal lead burden on infant weight and weight gain at one month of age among breastfed infants.Pediatrics. 2001; 107: 1016-1023Crossref PubMed Scopus (64) Google Scholar, 11Ettinger A. Tellez-Rojo M. Amarasiriwardena C. Bellinger D. Peterson K. Schwartz J. et al.Effect of breast milk lead on infant blood lead levels at 1 month of age.Environ Health Perspect. 2004; 112: 1381-1385Crossref PubMed Scopus (63) Google Scholar tibia,10Sanin L.H. Gonzalez-Cossio T. Romieu I. Peterson K.E. Ruiz S. Palazuelos E. et al.Effect of maternal lead burden on infant weight and weight gain at one month of age among breastfed infants.Pediatrics. 2001; 107: 1016-1023Crossref PubMed Scopus (64) Google Scholar and breast milk10Sanin L.H. Gonzalez-Cossio T. Romieu I. Peterson K.E. Ruiz S. Palazuelos E. et al.Effect of maternal lead burden on infant weight and weight gain at one month of age among breastfed infants.Pediatrics. 2001; 107: 1016-1023Crossref PubMed Scopus (64) Google Scholar, 11Ettinger A. Tellez-Rojo M. Amarasiriwardena C. Bellinger D. Peterson K. Schwartz J. et al.Effect of breast milk lead on infant blood lead levels at 1 month of age.Environ Health Perspect. 2004; 112: 1381-1385Crossref PubMed Scopus (63) Google Scholar lead at 1 month postpartum. Bone lead stores are mobilized during pregnancy and lactation.12Gulson B.L. Jameson C.W. Mahaffey K.R. Mizon K.J. Korsch M.J. Vimpani G. Pregnancy increases mobilization of lead from maternal skeleton.J Lab Clin Med. 1997; 130: 51-62Abstract Full Text PDF PubMed Scopus (256) Google Scholar Bone houses 95% of the lead in adults,13Barry P. Mossmann D. Lead concentration in human tissues.Br J Indust Med. 1970; 27: 339-351PubMed Google Scholar and as lead remains in bone for up to several decades after external lead exposure has declined, this mobilization may provide a significant exposure to lead by a growing fetus and breast-fed infant. Studies have found a positive association between bone loss with change in breast milk lead concentration.14Sowers M.R. Scholl T.O. Hall G. Jannausch M.L. Kemp F.W. Li X. et al.Lead in breast milk and maternal bone turnover.Am J Obstet Gynecol. 2002; 187: 770-776Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar Calcium supplementation has been shown to be moderately effective in lowering blood lead levels in lactating women, but only among women with relatively high lead burden (patella bone lead ≥5 μg/dL).15Hernandez-Avila M. Gonzalez-Cossio T. Hernandez-Avila J. Romieu I. Peterson K. Aro A. et al.Dietary calcium supplements to lower blood lead levels in lactating women: a randomized placebo-controlled trial.Epidemiology. 2003; 14: 206-212PubMed Google Scholar The good news is that lead in breast milk tends to be concentrated at 3% or less of maternal blood lead levels,16Gulson B. Jameson C. Mahaffey K. Mizon K. Patison N. Law A. et al.Relationships of lead in breast milk to lead in blood, urine and diet of the infant and mother.Environ Health Perspect. 1998; 106: 667-674Crossref PubMed Scopus (103) Google Scholar and significant elevations of milk lead concentrations in developed countries occur far less often than in developing countries.17Gulson B. Mizon K. Korsch M. Palmer J. Donnelly J. Mobilization of lead from human bone tissue during pregnancy and lactation-a summary of long-term research.Sci Tot Environ. 2003; 303: 79-104Crossref PubMed Scopus (203) Google Scholar The most recent US Preventive Task Force guidelines recommend against the routine screening for lead in asymptomatic pregnant women,18Screening for Elevated Blood Lead Levels in Children and Pregnant WomenUS Preventive Services Task Force. US Department of Health and Human Services, Washington, DC2006Google Scholar although New York State and Minnesota require blood lead screening of pregnant women. No federal government or national medical or nursing associations currently offer guidance on how best to monitor blood lead levels of pregnant or lactating mothers, or which breast-feeding children should be screened for lead early in their first year of life. In addition, measurement of lead in breast milk for clinical purposes is not feasible. What are potential risks for significant levels of lead in breast milk? Our data about this are still incomplete, but they include immigration from developing countries,19Klitzman S. Sharma A. Nicaj L. Vitkevich R. Leighton J. Lead poisoning among pregnant women in New York City: risk factors and screening practices.J Urban Health. 2002; 79: 225-237Crossref PubMed Scopus (30) Google Scholar maternal pica (which is more common in the southern United States and in African and Latin cultures),20Nchito M. Wenzel Geissler P. Mubila L. Friis H. Olsen A. Effects of iron and multimicronutrient supplementation on geophagy: a two-by-two factorial study among Zambian schoolchildren in Lusaka.Trans R Soc Trop Med Hygiene. 2004; 98: 218-227Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 21López L. Ortega Soler C. de Portela M. Pica during pregnancy: a frequently underestimated problem.Arch Latinoamericanos de nutrición. 2004; 54: 17-24PubMed Google Scholar use of imported cosmetics or certain complementary medications from developing countries, recent renovations of older homes, and occupations such as automobile repairs, work in firing ranges, or the manufacture of ceramics, batteries, and stained glass.22Shannon M. Severe lead poisoning in pregnancy.Ambul Pediatr. 2003; 3: 37-39Abstract Full Text Full Text PDF PubMed Scopus (65) Google Scholar, 23Gundacker C. Pietschnig B. Wittmann K.J. Lischka A. Salzer H. Hohenauer L. et al.Lead and mercury in breast milk.Pediatrics. 2002; 110: 873-878Crossref PubMed Scopus (112) Google Scholar, 24Ursinyova M. Masanova V. Cadmium, lead and mercury in human milk from Slovakia.Food Additives Contaminants. 2005; 22: 579-589Crossref PubMed Scopus (78) Google Scholar In addition, women who had significant lead exposure as children may have elevations of lead in breast milk.25Chantry C.J. Auinger P. Byrd R.S. Lactation among adolescent mothers and subsequent bone mineral density.Arch Pediatr Adolesc Med. 2004; 158: 650-656Crossref PubMed Scopus (67) Google Scholar So what should we take away from this important study? Yes, breast milk may be a source of lead exposure for breast-feeding infants, but at this time it appears that in most cases the risks associated with the small amount of exposure will be far outweighed by the benefits of breast-feeding. In some cases, assessment of pregnant and lactating mothers' blood lead may be useful, but this is not indicated for all women or all breast-feeding infants. As long as the lactating mother's blood lead level is <40 μg/dL, there is no reason to stop breastfeeding,5Lozoff B. Jimenez E. Wolf A. Angelilli M. Zatakia J. Jacobson S. et al.Higher infant blood lead levels with longer duration of breastfeeding.J Pediatr. 2009; 155: 663-667Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar although if breast-feeding mothers have blood lead levels >5 μg/dL, one might consider checking the infant's blood lead. As long as the infant's lead level remains <5 μg/dL, there appears to be no reason to stop breast-feeding. In the meantime, there is a real need for evidence-based guidelines on lead screening of lactating women and breast-fed infants, valid and practical screening questionnaires to identify which pregnant and lactating women and which breast-feeding infants should be screened for blood lead levels. In addition, we need far better estimates of the numbers and characteristics of pregnant and lactating women who should be screened and far more knowledge of, and better regulation of, complementary and alternative medicines, cosmetics, and dietary supplements. Higher Infant Blood Lead Levels with Longer Duration of BreastfeedingThe Journal of PediatricsVol. 155Issue 5PreviewTo determine whether longer breastfeeding is associated with higher infant lead concentrations. Full-Text PDF