BONE TURNOVER AND DENSITY IN HEALTHY WOMEN DURING BREAST-FEEDING AND AFTER MEANING

To investigate the changes in maternal bone density and turnover assoc iated with lactation we ran a longitudinal study in fully breastfeedin g women (age 26.3+/-4.1 years, mean+/-SD) at the first (stage I, n = 3 0) and sixth (stage II, n = 25) months postpartum and 6 months after w eaning (stage III, n = 20), and in a contemporary control group of non -nursing women. At each time point bone density, serum calcium, phosph orus, alkaline phosphatases, parathyroid hormone (PTH), osteocalcin, f ollicle stimulating hormone (FSH), estradiol (E(2)), prolactin (PRL) u rinary hydroxyproline and creatinine (OH-P/Cr) were measured in both g roups. 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 a t stage I). Biochemical markers of bone turnover were higher (p<0.05) in nursing than in non-nursing women at stages I and II, while in stag e III only OH-P/Cr was elevated. The lumbar spine (L2-4) bone mineral density was similar in the two groups at the beginning of the study (1 .148 +/- 0.111 g/cm(2) in nursing women vs 1.211 +/- 0.102 g/cm(2) in non-nursing women; p = 0.56), but it was lower in nursing women at sta ge II (1.144 +/- 0.110 g/cm(2) vs 1.216 +/- 0.095 g/cm(2) respectively ; p<0.05). Right cm 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 0.91 8 +/- 0.114 vs 0.975 +/- 0.098 in stage II respectively; p<0.05, ANOVA ). After weaning, lumbar spine and femoral neck bone density increased by 6% and 8% respectively (p<0.05, ANOVA). No correlation was found b etween changes in bone turnover markers or bone density and parity, fr equency and duration of nursing episodes, body weight, body mass index , and plasma PRL, E(2) and PTH levels. We conclude that in nursing wom en with a daily calcium intake at the recommended dietary allowance (> 1200 mg/day), full breastfeeding extending over 6 months is characteri zed by increased maternal bone turnover and a transient bone loss whic h normalizes after weaning.