Does donating human milk result in greater compromise to the bone mass of breastfeeding mothers?

OBJECTIVE: Although the effects of lactation on bone mass are frequently discussed, it is unknown whether these effects are intensified in breastfeeding mothers (BFM) who become donors (BFM-donors). Thus, the objective was to evaluate alterations in bone densitometry and bone metabolism in BFM-donors during six months of follow-up, compared with BFM-controls who did not donate maternal milk, to determine whether these changes would be intensified by the volume donated. METHODS: Data were obtained from two groups: 39 BFM-donors (six and twelve months postpartum) and 38 BFM-controls (up to 15 days [baseline] and six months postpartum). Donated milk volume, body mass index, and bone mineral density (BMD) of the lumbar spine, proximal femur, and total body were assessed by densitometry. Calcium, phosphorus, parathyroid hormone, 25(OH)D, estradiol, osteocalcin, bone alkaline phosphatase, and carboxy-terminal telopeptide were measured. Comparisons were performed using Student's t-test, followed by repeated-measures models and ANCOVA adjusted for confounders when appropriate. Effect size and statistical power were also calculated. RESULTS: BFM-donors showed bone mass mobilization similar to BFM-controls at six months, without influence of donated volume (9.0 ± 8.2 L). From six to 12 months postpartum, lumbar spine and femur BMD values increased (5% and 1.5%). CONCLUSIONS: Comparing BFM-donors at 12 months, versus BMF-controls at 15 days, even with continued complementary breastfeeding, densitometric results tended to return to the means seen 15 days postpartum. There were no correlations between BMD, bone markers, and total volume of donated milk.