A Study on Microbial and Macronutrient Composition of Breast Milk Varies with Lactation Duration

Abstract

Complementary feeding and continuation of breast feeding is directed and advised by the national and international child health agencies. Breast milk, a complex biological fluid, shows changes in its cellular, microbial and nutrient composition as lactation progresses. In a cross-sectional study, hospital-based pilot project showed the composition of microbial and macronutrients and compared their differences before and after first six months of lactation. Staphylococcus aureus was the predominant bacterium found in breast milk, and 45% (15/33) of samples within first six months and only 13% (3/22) from those more than six months of lactation showed any bacterial growth (p=0.013). The protein content was less in breast milk samples after six months compared to those within six months of lactation (mean difference, 95% CI: 0.33 (0.10, 0.55) gm/dL, p=0.005). After controlling the lactation period, bacterial culture positivity in breast milk was associated directly with the breast milk protein content. Our pilot study observations indicate the need to study microbial and nutrient changes in breast milk as lactation advances, in a longitudinal study with larger sample size, and investigate its associations with maternal factors, infant growth, establishment of infant gut microbiota and possible role in environmental enteric dysfunction.