Macronutrient, immunoglobulin A and total antioxidant capacity profiles of human milk: cross-sectional surveys at ages 6, 12, 18 and 24 months.
Abstract Background: An extended duration of breastfeeding of up to two years is encouraged by many health authorities, but information regarding the composition of milk after one year postpartum is limited. The goal of this study was to determine the associations of macronutrient contents, immunoglobulin A (IgA) levels, and the total antioxidant capacity (TAC) in human milk (HM) with the month of lactation from 1 to 24 months postpartum.Methods: Milk samples were collected from mothers with healthy full-term children who had been lactating from 1 to 24 months from January 2019 to April 2019. The HM was biochemically analyzed for protein and carbohydrate contents by colorimetric assays. The fat content was determined by capillary centrifugation, and the energy content was calculated from the results of centrifugation assays. IgA levels and the TAC were determined by ELISA and a Trolox equivalent antioxidant capacity (TEAC) assay, respectively. Pearson’s correlation coefficient and Spearman’s rank correlation coefficient were used to determine associations between milk composition and the month of lactation, and multiple regression analysis was used to assess the association between the covariates and milk composition. Differences were considered significant at p < 0.05.Results: One hundred eighty-four milk samples were analyzed. The month of lactation was positively associated with the fat concentration (B = 0.31, SE = 0.09, p = 0.001), energy content (B = 3.11, SE = 0.92, p = 0.001), and IgA (B = 4.17, SE = 1.08, p < 0.001) but negatively associated with the carbohydrate concentration (B = -0.22, SE = 0.01, p = 0.04). No association was observed between the month of lactation and the protein concentration and TAC after adjustment for maternal age, maternal BMI, birth order, and breastfeeding frequency.Conclusions: The month of lactation was found to be positively associated with the fat, energy, and IgA in HM for up to two years postpartum and slightly but significantly negatively associated with carbohydrate concentration. More prospective cohort studies are needed to obtain evidence-based knowledge regarding the changes in HM composition throughout the course of lactation.