A pilot study on the protein composition of induced nonpuerperal human milk

Our understanding of the components of human puerperal milk is extensive and increasing, yet the literature on nonpuerperal human milk has been limited to studies that measure the success of induced lactation.

This study aimed to describe the composition of total protein and key bioactive proteins when lactation is induced in nonpuerperal women.

Two women who induced lactation in the absence of pregnancy provided weekly milk samples over a 2-month period for analysis of total protein, secretory immunoglobulin A (sIgA), lysozyme, and lactoferrin. Composition was compared to the mature milk of 3 puerperal control subjects who were 11 months postpartum.

Median total protein for subject A was 2.30 g/dL (interquartile range [IQR] = 0.46) and showed a significant downward trend over time (P < .0001), whereas the median total protein for subject B was 2.21 g/dL (IQR = 0.18) and showed a nonsignificant decline (P = .232). Total protein in both nonpuerperal subjects was elevated compared to control subjects. Secretory IgA activity declined for both nonpuerperal subjects over time, whereas lysozyme concentrations increased over time. Both sIgA and lysozyme approached the levels seen in the puerperal controls. Lactoferrin levels remained stable for both nonpuerperal subjects and were elevated compared to puerperal milk samples.

This pilot study suggests that nonpuerperal milk has similar or higher levels of total protein, sIgA, lactoferrin, and lysozyme compared to puerperal, mature milk at 11 months postpartum, which warrants more attention as adoptive mothers increasingly choose to induce lactation.