Macronutrient, immunoglobulin A and total antioxidant capacity profiles of human milk: cross-sectional surveys at ages 6, 12, 18 and 24 months.

Abstract

Background: A longer 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. 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 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: Based on our results, fat, energy, and IgA contents in HM were positively associated with the month of lactation, and a slight but significant negative association was detected for the carbohydrate concentration up to two years postpartum.