Howard Hu, MD, Sc.D.
Background: Research has focused a great deal of attention on the risks for the developing fetus from circulating levels of lead in maternal blood, but much less attention has been given to the danger lead in breast milk may have on the cognitive development of young children. Although there are many well-recognized benefits of breast-feeding for mothers and infants, there are no clear guidelines on breast-feeding for women who have high circulating or bone levels of lead. Previous research has shown that maternal bone lead stores, from past environmental exposures, are mobilized during pregnancy and lactation as calcium stores are drawn upon. However, there is less information on the transfer of lead to breast milk.
To investigate whether maternal stores of lead can be transferred to breast milk, this NIEHS-supported team performed an epidemiologic study with 310 lactating women in Mexico City, Mexico. Maternal blood, umbilical cord blood, and breast milk samples were analyzed for lead content. Maternal bone lead concentration was determined non-invasively.
Advance: Levels of lead in breast milk ranged from 0.21 to 8.02 micrograms/liter with an average of 1.1 micrograms/liter. In comparison, maternal blood lead ranged from 18 to 300 micrograms/liter. A positive correlation existed between breast milk lead and blood lead level. The data show that for a rise of 50 micrograms of lead/liter of blood, the breast milk lead level rose 33%. Comparatively equal increases in bone lead content resulted in smaller increases in breast milk (14% and 5% for patellar lead and tibia lead respectively).
Implication: These results indicate that even among a population of women with relatively high lifetime exposure to lead, breast milk lead levels are low. These levels are influenced by both current exposures to lead as well as the mobilization of lead from bone stores during pregnancy and lactation. There is no safe level of lead exposure; however, the authors conclude that despite the potential for lead exposure, breast milk is the most complete nutritional source for young infants.
Citation: Ettinger AS, Tellez-Rojo MM, Amarasiriwardena C, Gonzalez-Cossio T, Peterson KE, Aro A, Hu H, Hernandez-Avila M. Levels of lead in breast milk and their relation to maternal blood and bone lead levels at one month postpartum. Environ Health Perspect. 2004 Jun;112(8):926-31.