Bone turnover and density in healthy women during breastfeeding and after weaning

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Abstract
To investigate the changes in maternal bone density and turnover associated with lactation we ran a longitudinal study in fully breastfeeding women (age 26.3±4.1 years, mean±SD) at the first (stage I, n=30) and sixth (stage II, n=25) months postpartum and 6 months after weaning (stage III, n=20), and in a contemporary control group of non-nursing women. At each time point bone density, serum calcium, phosphorus, alkaline phosphatases, parathyroid hormone (PTH), osteocalcin, follicle stimulating hormone (FSH), estradiol (E2), prolactin (PRL) urinary hydroxyproline and creatinine (OH-P/Cr) were measured in both groups. The daily calcium intake of nursing women (1479±590 mg/day at stage I) was higher than in non-nursing women (536±231 mg/day at stage I). Biochemical markers of bone turnover were higher (p2 in nursing women vs 1.211±0.102 g/cm2 in non-nursing women; p=0.06), but it was lower in nursing women at stage II (1.144±0. 110g/cm2vs 1.216±0.095 g/cm2 respectively; p<0.05). Right femoral neck bone density decreased by 3% between stages I and II in nursing women but did not differ from values in non-nursing women (0.947±0.110 vs 0.973±0.108 in stage I and 0.918±0.114 vs 0.975±0.098 in stage II respectively; ps<0.05, ANOVA). After weaning, lumbar spine and femoral neck bone density increased by 6% and 8% respectively (p1200 mg/day), full breastfeeding extending over 6 months is characterized by increased maternal bone turnover and a transient bone loss which normalizes after weaning.