Association Between Breastfeeding Intensity and Mammary Gland Involution Markers in Early Postpartum Among Women from Low-Income Households

<b><i>Background:</i></b> The aim was to examine the associations between breastfeeding intensity and changes in concentrations of mammary gland involution markers (protein and lactose) among mothers participating in federal food assistance programs. <b><i>Methods:</i></b> Pregnant women in their third trimester who planned to breastfeed were recruited from local prenatal clinics (<i>n</i> = 25). After delivery, six weekly home visits were conducted to collect human milk samples and 24-hour infant feeding recalls. Milk protein and lactose concentrations were measured utilizing Bicinchoninic Acid and Megazyme assays, respectively. Bivariate tests were carried out using a statistical significance of <i>p</i> < 0.05. <b><i>Results:</i></b> Majority (84%) of our participants were either African American or of Latino origin. About one-fourth of our participants were primiparous and the average monthly household income was $3,150 with an average household size of 4. In week 2 postpartum, 18 mothers had a 100% breastfeeding intensity, while in week 6 it decreased to 16 mothers. A significant difference in milk protein concentration was seen between exclusive and mixed-feeding mothers from weeks 2 to 6; meanwhile, for lactose concentrations, the significant differences were seen only in weeks 3 and 4 (<i>p</i> < 0.005). Protein changes were negatively associated with breastfeeding intensity (as breastfeeding intensity went up, protein decreased), while lactose changes were positively associated with breastfeeding intensity (protein <i>r</i> = -0.5578; lactose <i>r</i> = 0.6571). <b><i>Conclusions:</i></b> Significant associations between intensity of breast milk feeding and mammary gland involution markers highlight the sensitivity of the mammary gland to mixed feedings in the early postpartum period.