Academic journal article Environmental Health Perspectives

Levels of Lead in Breast Milk and Their Relation to Maternal Blood and Bone Lead Levels at One Month Postpartum

Academic journal article Environmental Health Perspectives

Levels of Lead in Breast Milk and Their Relation to Maternal Blood and Bone Lead Levels at One Month Postpartum

Article excerpt

Despite the many well-recognized benefits of breast-feeding for both mothers and infants, detectable levels of lead in breast milk have been documented in population studies of women with no current environmental or occupational exposures. Mobilization of maternal bone lead stores has been suggested as a potential endogenous source of lead in breast milk. We measured lead in breast milk to quantify the relation between maternal blood and bone lead levels and breast-feeding status (exclusive vs. partial) among 310 lactating women in Mexico City, Mexico, at 1 month postpartum. Umbilical cord and maternal blood samples were collected at delivery. Maternal breast milk, blood, and bone lead levels were obtained at 1 month postpartum. Levels of lead in breast milk ranged from 0.21 to 8.02 [micro]g/L (ppb), with a geometric mean (GM) of 1.1 [micro]g/L; blood lead ranged from 1.8 to 29.9 [micro]g/dL (GM = 8.4 [micro]g/dL); bone lead ranged from < 1 to 67.2 lag/g bone mineral (patella) and from < 1 to 76.6 [micro]g/g bone mineral (tibia) at 1 month postpartum. Breast milk lead was significantly correlated with umbilical cord lead [Spearman correlation coefficient ([r.sub.S]) = 0.36, p < 0.0001] and maternal blood lead ([r.sub.S] = 0.38, p < 0.0001) at delivery and with maternal blood lead ([r.sub.S] = 0.42, p < 0.0001) and patella lead ([r.sub.S] = 0.15, p < 0.01) at 1 month postpartum. Mother's age, years living in Mexico City, and use of lead-glazed ceramics, all predictive of cumulative lead exposure, were not significant predictors of breast milk lead levels. Adjusting for parity, daily dietary calcium intake (milligrams), infant weight change (grams), and breast-feeding status (exclusive or partial lactation), the estimated effect of an interquartile range (IQR) increase in blood lead (5.0 [micro]g/dL) was associated with a 33% increase in breast milk lead [95% confidence interval (CI), 24 to 43%], whereas an IQR increase in patella lead (20 [micro]g/g) was associated with a 14% increase in breast milk lead (95% CI, 5 to 25%). An IQR increase in tibia lead (12.0 [micro]g/g) was associated with a 5% increase in breast milk lead (95% CI, -3% to 14%). Our results indicate that even among a population of women with relatively high lifetime exposure to lead, levels of lead in breast milk are low, influenced both by current lead exposure and by redistribution of bone lead accumulated from past environmental exposures. Key words: blood lead, breast milk lead, breast-feeding, KXRF bone lead, lactation. Environ Health Perspect 112:926-931 (2004). doi:10.1289/ehp.6615 available via http://dx.doi.org/[Online 7 April 2004]

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Although substantial attention has been given to the risks for the developing fetus from circulating lead in maternal blood, much less consideration has been given to the presence of lead in breast milk. There are no clear guidelines regarding breast-feeding to provide counseling to women with elevated blood or bone lead levels (Sinks and Jackson 1999). Previous research has shown that maternal bone lead stores, accumulated from past environmental exposures, are mobilized to a marked degree during pregnancy and lactation (Gulson et al. 1997 1998b; Hernandez-Avila et al. 1996; Hertz-Picciotto et aL 2000; Hu et al. 1996; Rothenberg et al. 2000). Breast-feeding practices and maternal bone lead levels have been shown to be important predictors of maternal blood lead levels over the course of lactation (Tellez-Rojo et al. 2002). However, there is less information available about the transfer of lead to breast milk.

Lactation requires a substantial redistribution of maternal calcium that is marked by mobilization of calcium from bone stores (Sowers 1996). It is estimated that up to 5% of bone mass is mobilized during lactation (Hayslip et al. 1989; Sowers 1996); thus, lead accumulated in bone from past exposures may be released into blood and excreted into breast milk. …

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