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August 21, 1996

Elevated Parathyroid Hormone-Related Peptide Associated With Lactation and Bone Density Loss

Author Affiliations

From the Departments of Epidemiology (Dr Sowers, and Mss Crutchfield, and Russell-Aulet), Biostatistics (Dr Schork and Mss Janney and Zhang), Internal Medicine (Dr Shapiro), and Obstetrics and Gynecology (Drs Sowers and Randolph), University of Michigan, Ann Arbor; the Department of Pediatrics, Medical University of South Carolina, Charleston (Dr Hollis); and the Department of Obstetrics and Gynecology, University of Southern California School of Medicine, Los Angeles (Dr Stanczyk).

JAMA. 1996;276(7):549-554. doi:10.1001/jama.1996.03540070045029

Objective.  —To investigate the hypothesis that parathyroid hormone—related peptide (PTHrP) may be involved with bone loss and recovery as a means of providing adequate calcium and phosphate to infants.

Design.  —An 18-month prospective cohort study.

Setting.  —General community setting with recruitment occurring at birthing education classes.

Participants.  —Volunteer sample of 115 postpartum healthy women aged 20 to 40 years, and 0 or 1 parity prior to parturition with no intent to breast-feed or intent to breast-feed at least 6 months.

Main Outcome Measures.  —Parathyroid hormone-related peptide, prolactin, estradiol, 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D, femoral bone mineral density, and bone turnover markers were measured in 115 postpartum women at 2 weeks, 2 months, 4 months, 6 months, 12 months, and 18 months postpartum. Lumbar bone mineral density was measured at 2 weeks, 6 months, 12 months, and 18 months postpartum.

Results.  —Elevated PTHrP values were significantly associated (P<.001) with breast-feeding status, elevated prolactin levels, and lower serum estradiol levels, conditions occurring during lactation. Furthermore, elevated PTHrP levels were negatively and significantly associated (P<.01) over time with bone mineral density change at both the spine and the femoral neck, even after accounting for prolactin levels, breast-feeding status, return of menstruation, estradiol levels, PTH levels, 1,25-dihydroxyvitamin D levels, dietary calcium intake, physical activity, and body size.

Conclusion.  —These data clearly support the hypothesis that PTHrP is an alternative mechanism associated with bone loss and recovery during and subsequent to lactation.