Nitrogen Distribution in Human Milk from 2 to 16 Weeks Postpartum

The objective of this study was to determine how the major nitrogen components in human milk vary as total nitrogen in the milk changes. Milk samples were collected from 10 mothers at 2, 6, 12, and 16 wk postpartum. The major nitrogen components compared were total, nonprotein, urea, protein, casein, and whey nitrogens. Total nitrogen decreased from 2.18 mg/ml at 2 wk to 1.76 mg/ml at 16 wk. The percentage of nonprotein nitrogen was 19% and remained constant with time postpartum. Urea nitrogen averaged .14 mg/ml and also remained constant. Protein nitrogen decreased from 1.77 mg/ml at 2 wk to 1.42 mg/ml at 16 wk. As the total nitrogen in milk changed, the percentages of nonprotein nitrogen, whey nitrogen, and casein nitrogen remained relatively constant.