Bone Mineral Changes During and After Lactation
FRANCO POLATTI, MD, EZIO CAPUZZO, MD, FRANCO VIAZZO, MD, ROSSELLA COLLEONI, MD and CATHERINE KLERSY, MD
From the Clinica Ostetrico-Ginecologica, Università di Pavia, and Biometry - Scientific Direction, IRCCS Policlinico San Matteo, Pavia, Italy.
Address reprint requests to: Franco Polatti, MD, Clinica Ostetrico-Ginecologica, IRCCS Policlinico San Matteo, Piazzale Golgi 2, 27100 Pavia, Italy, E-mail: [email protected]
Objective: To investigate variations in bone mineral density during lactation and throughout the 12 months after scheduled cessation of lactation in relation to the resumption of ovarian function.
Methods: Three hundred eight mothers who decided to lactate were scheduled to fully breast-feed for 6 months, followed by a 1-month weaning period, and then suppress lactation with cabergoline. Their bone mineral density variations were compared with those of a control group of nonlactating mothers during the first 18 months postpartum. Half the lactating women were given daily oral calcium supplements of 1 g in an open design.
Results: There was a significant progressive decrease in bone mineral density in lactating women over the first 6 months, followed by recovery of bone mass up to levels that at 18 months were higher than baseline. In nonlactating women, bone mineral density increased progressively after delivery, and at 18 months postpartum had increased by 1.1–1.9% compared with baseline. Compared with lactating women who resumed menstruation within 5 months of delivery, breast-feeding mothers with longer amenorrhea initially lost more bone, but they also gained significantly more bone after resumption of menses, so there were no differences at 18 months postpartum. Oral calcium supplementation decreased bone loss, but had only a transient effect.
Conclusion: A scheduled lactation period of 6 months, followed by a 1-month weaning period, allowed bone mineral density to reach higher values compared with early postpartum, regardless of calcium supplementation and duration of postpartum amenorrhea.
Obstetrics & Gynecology 1999;94:52-56.
In recent years, much attention has been focused on bone mass, with the aim of developing strategies to prevent bone loss. Marked changes in calcium metabolism were reported during lactation,1 related to amount of breast milk produced, diet, and duration of lactation. The decrease in bone mineral density averages 4–6% during the first 6 months of lactation.2,3 Previous reports of changes in bone mass postpartum were contradictory, with diminished,4,5 unchanged,6,7 or increased bone mineral density.8 Such discrepancies likely result from different timing of measurements and differences in techniques to measure bone mineral density and anatomic sites evaluated in regard to the ratio of cortical to trabecular bone, typical of sites investigated. During lactation, the women have a period of considerable hypoestrogenemia, which negatively affects calcium and phosphate metabolism, as seen in amenorrhea,9,10 and is widely documented after menopause.11,12 During lactation the return of ovarian function varies greatly, so that remarkable differences in bone mass might develop among individuals. Most previous studies were limited by wide ranges in duration of lactation and weaning. To control for those variations, we investigated bone mass variations at well-defined time points postpartum with a fixed length of lactation and weaning.
The aim of this study was to investigate variations of bone mineral density during lactation and throughout the 12 months after the scheduled cessation of lactation, in relation to resumption of ovarian function and calcium supplementation.