Lactation and bone turnover: a conundrum of marked bone loss in the setting of coupled bone turnover.
BACKGROUND
Mothers who exclusively breastfeed lose up to 10% of their bone mass. This is primarily mediated by PTHrP, in combination with low estrogen levels. The mechanisms underlying this marked bone loss are unknown. Uncoupling of bone turnover, which is seen in other prototypical states of bone loss, would seem the likely explanation. However, the most current markers of bone turnover have not been studied in human lactation.


OBJECTIVE
The purpose of this study was to assess bone formation in lactating humans using the most current bone turnover markers.


METHODS
We conducted a prospective cohort study with repeated measures of bone metabolism in a volunteer sample of 49 women, recruited into three study groups: lactating, bottle feeding, and healthy controls. The postpartum women were studied at 6-8 and 12-14 wk postpartum, whereas the controls were studied at the follicular phase of their menstrual cycles.


METHODS
Biochemical markers of bone turnover were assessed.


RESULTS
Mean serum C-telopeptide of type I collagen, a sensitive marker of bone resorption, was approximately 2-fold higher in lactating women as compared with bottle-feeding and healthy controls (P = 0.037 and P < 0.001, respectively). Surprisingly, amino-terminal telopeptides of procollagen 1, the most current marker of bone formation, bone-specific alkaline phosphatase, and osteocalcin were all significantly higher in the lactating group as compared with controls (P < 0.001, P = 0.002, and P < 0.001, respectively).


CONCLUSIONS
In contrast to prototypical states of rapid bone loss (myeloma, cancer, and immobilization) in which markers of bone turnover display marked uncoupling, lactational bone loss, as assessed in this small exploratory study, is distinct, showing comparably rapid bone loss in the face of apparent osteoclast-osteoblast coupling.
Division of Endocrinology, University of Pittsburgh School of Medicine, NW 810, UPMC Montefiore, 3459 5th Avenue, Pittsburgh, Pennsylvania 15213, USA.
Raquel M
RM
Carneiro
Linda
L
Prebehalla
Mary Beth
MB
Tedesco
Susan M
SM
Sereika
Maryann
M
Hugo
Bruce W
BW
Hollis
Caren M
CM
Gundberg
Andrew F
AF
Stewart
Mara J
MJ
Horwitz
D000328:Adult; D000469:Alkaline Phosphatase / Q000097:blood; D015415:Biomarkers / Q000097:blood; D001862:Bone Resorption / Q000235:genetics / Q000503:physiopathology*; D001842:Bone and Bones / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D015331:Cohort Studies; D004958:Estradiol / Q000097:blood; D005260:Female; D006801:Humans; D007774:Lactation / Q000502:physiology*; D015675:Osteocalcin / Q000097:blood; D051757:PAX5 Transcription Factor / Q000097:blood; D010281:Parathyroid Hormone / Q000097:blood; D010748:Phosphopeptides / Q000097:blood; D011347:Procollagen / Q000097:blood; D011446:Prospective Studies; D014807:Vitamin D / Q000097:blood; D055815:Young Adult
D015415:Biomarkers; C062121:N-propeptide type I collagen; D051757:PAX5 Transcription Factor; C497281:PAX5 protein, human; D010281:Parathyroid Hormone; D010748:Phosphopeptides; D011347:Procollagen; D015675:Osteocalcin; D014807:Vitamin D; D004958:Estradiol; C548267:ALPL protein, human; D000469:Alkaline Phosphatase; D002118:Calcium