| Study of the Effect of Lactational Bone Loss on Blood Lead Concentrations in Humans John D. Osterloh1,2 and Thomas J. Kelly2 1Department of Laboratory Medicine; 2Department of Medicine, University of California San Francisco, San Francisco, California 94110 USA Abstract
Lactation and other clinical states of high bone turnover have been suggested to release lead (Pb) stored in bone into blood and tissues. Previous observations on the influences of lactation have been anecdotal, or at high blood Pb concentrations with varying past exposures, or complicated by postpartum fluid changes. A prospective observational study was performed to investigate possible changes in blood lead concentrations at multiple intervals during lactation for 6 months postpartum and to relate changes in blood lead concentrations to changes in bone density and other variables. Volunteer pregnant subjects (n = 58) were enrolled from a midwifery service at an academic public health hospital. Subjects were mostly Hispanic, recently immigrated, of low economic status, not receiving supplemental calcium, and had low blood Pb concentrations (2.35 ± 2.05 µg/dl at enrollment) . Bone density losses over 6 months for the group averaged -2.46 ± 6.33% at the vertebral spine and -0.67 ± 5.21% at the femoral neck. In predicting final bone density, apart from initial bone density only the total number of breast-feedings was a significant independent variable of the variables tested, accounting for an additional 12% of the variability. No changes in blood Pb concentrations were seen over the interval beyond 2 weeks postpartum (minimum detectable change was 0.4 µg/dl) . There was no relation between the changes in bone density and changes in blood Pb or the integrated blood Pb over the 2-week to 6-month period. Normal (nonlactating) bone resorption rates contribute a large fraction of the Pb in blood during low-exposure circumstances. However, during lactation the increase in bone resorptive processes is probably relatively small with a larger decrease in deposition accounting for net bone loss, as suggested by other investigations. Thus, concomitant release of Pb from bones of lactating subjects with low blood lead concentrations on this background of high normal resorption was not large enough for detection. Key words: blood lead, bone density, lactation, Pb. Environ Health Perspect 107:187-194 (1999) . [Online 26 January 1999] http://ehpnet1.niehs.nih.gov/docs/1999/107p187-194osterloh/ abstract.html Address correspondence to J.D. Osterloh, Room 3501A, San Francisco General Hospital, 1001 Potrero Avenue, San Francisco, CA 94110 USA. The cooperation of the Nurse Midwifery Service at San Francisco General Hospital is acknowledged. Gratitude is expressed to Nancy Myrick, who performed all interviews, bone density exams, and phlebotomy, and to Bernard Hata for blood Pb determinations. The use of the dual-energy x-ray densitometer through the Division of Endocrinology (grant DK45833) is acknowledged with special thanks to Kathleen Mulligan. This study was funded by NIEHS grant ES04580. Received 10 July 1998 ; accepted 18 November 1998.
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