title: Maternal blood, plasma, and breast milk lead: lactational transfer and contribution to infant exposure.
abstract: BACKGROUND
  Human milk is a potential source of lead exposure. Yet lactational transfer of lead from maternal blood into breast milk and its contribution to infant lead burden remains poorly understood.
  
  
  OBJECTIVE
  We explored the dose-response relationships between maternal blood, plasma, and breast milk to better understand lactational transfer of lead from blood and plasma into milk and, ultimately, to the breastfeeding infant.
  
  
  METHODS
  We measured lead in 81 maternal blood, plasma, and breast milk samples at 1 month postpartum and in 60 infant blood samples at 3 months of age. Milk-to-plasma (M/P) lead ratios were calculated. Multivariate linear, piecewise, and generalized additive models were used to examine dose-response relationships between blood, plasma, and milk lead levels.
  
  
  RESULTS
  Maternal lead levels (mean±SD) were as follows: blood: 7.7±4.0 μg/dL; plasma: 0.1±0.1 μg/L; milk: 0.8±0.7 μg/L. The average M/P lead ratio was 7.7 (range, 0.6-39.8) with 97% of the ratios being >1. The dose-response relationship between plasma lead and M/P ratio was nonlinear (empirical distribution function=6.5, p=0.0006) with the M/P ratio decreasing by 16.6 and 0.6 per 0.1 μg/L of plasma lead, respectively, below and above 0.1 μg/L plasma lead. Infant blood lead level (3.4±2.2 μg/dL) increased by 1.8 μg/dL per 1 μg/L milk lead (p<0.0001, R2=0.3).
  
  
  CONCLUSIONS
  The M/P ratio for lead in humans is substantially higher than previously reported, and transfer of lead from plasma to milk may be higher at lower levels of plasma lead. Breast milk is an important determinant of lead burden among breastfeeding infants.
authors.affiliation: Department of Chronic Disease Epidemiology, School of Public Health, Yale University, New Haven, Connecticut, USA.
authors.forename: Adrienne S
authors.initials: AS
authors.lastname: Ettinger
authors.forename: Ananya
authors.initials: A
authors.lastname: Roy
authors.forename: Chitra J
authors.initials: CJ
authors.lastname: Amarasiriwardena
authors.forename: Donald
authors.initials: D
authors.lastname: Smith
authors.forename: Nicola
authors.initials: N
authors.lastname: Lupoli
authors.forename: Adriana
authors.initials: A
authors.lastname: Mercado-García
authors.forename: Hector
authors.initials: H
authors.lastname: Lamadrid-Figueroa
authors.forename: Martha Maria
authors.initials: MM
authors.lastname: Tellez-Rojo
authors.forename: Howard
authors.initials: H
authors.lastname: Hu
authors.forename: Mauricio
authors.initials: M
authors.lastname: Hernández-Avila
mesh_terms: D001942:Breast Feeding; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007774:Lactation; D007854:Lead / Q000097:blood* / Q000378:metabolism*; D008895:Milk, Human / Q000737:chemistry*; D010949:Plasma / Q000737:chemistry*; D011247:Pregnancy
chemical_list: D007854:Lead