Bone changes after 3 mo of lactation: influence of calcium intake, breast-milk output, and vitamin D-receptor genotype.
Factors influencing the change in bone mineral after 3 mo of lactation were investigated in 47 breast-feeding mothers, 11 formula-feeding mothers, and 22 nonpregnant, nonlactating control subjects. At 6-8 wk postpartum, the breast-feeding group had a mean (+/-SD) calcium intake of 34.8+/-13.2 mmol/d and breast-milk volume, calcium concentration, and calcium output of 0.865+/-0.230 L/d, 7.41+/-1.25 mmol/L, and 6.41+/-2.00 mmol/d, respectively. There was no relation between calcium intake and any breast-milk variable. Dual-energy X-ray absorptiometry of the whole body, spine, hip, and forearm was performed at 0.5 and 3 mo. There were significant decreases in bone mineral content at the spine (3.96%; 95% CI: 4.86%, 3.06%), femoral neck (2.39%; 95% CI: 3.61%, 1.17%), total hip (1.51%; 95% CI: 2.45%, 0.60%), and whole body (0.86%; 95% CI: 1.29%, 0.43%) in breast-feeding mothers but not in formula-feeding mothers or nonpregnant, nonlactating women. These changes were not related to calcium intake, breast-milk calcium concentration, vitamin D-receptor genotype, postpartum weight change, or use of the progesterone-only contraceptive pill. After adjustment for bone area, breast-milk volume and height were identified as significant predictors at the spine, such that greater decreases were associated with taller mothers (P = 0.007) and those with greater breast-milk volume (P = 0.001). This finding suggests that the marked bone mineral changes observed in breast-feeding mothers represented a physiologic response to lactation that was independent of dietary calcium supply.
Laskey
M A
MA
MRC Dunn Nutrition Centre, Cambridge, United Kingdom. ann.laskey@mrc-dunn.cam.ac.uk
Prentice
A
A
Hanratty
L A
LA
Jarjou
L M
LM
Dibba
B
B
Beavan
S R
SR
Cole
T J
TJ
D015502:Absorptiometry, Photon; D000328:Adult; D015519:Bone Density; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002136:Calcium, Dietary / Q000008:administration & dosage*; D005260:Female; D005838:Genotype; D006801:Humans; D007774:Lactation / Q000502:physiology*; D008895:Milk, Human / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000235:genetics*; D013997:Time Factors
D002136:Calcium, Dietary; D018167:Receptors, Calcitriol; D002118:Calcium