Human Milk Banking: Longitudinal Composition in Second Postpartum Year

According to the United Nation’s Children’s Emergency Fund (UNICEF), exclusively breastfed infants are 14 times less likely to die within the first six months of life as compared to their non-breastfed peers. This is of particular importance in areas with limited access to clean water but holds true even in industrialized nations. Indeed, both the World Health Organization (WHO) and UNICEF recommend breastfeeding for a minimum of two years.

Human milk banking and the use of donor milk in hospitals can support long-term breastfeeding goals, improve health outcomes and lower healthcare costs, particularly for medically fragile infants. Institutions that support human milk banking include WHO, the American Academy of Pediatrics and the Office of the Surgeon General of the United States.

Despite this, many milk banks place limits on milk donors, with some excluding potential donors as early as six months postpartum. Of the 13 milk banks associated with the Human Milk Banking Association of North America, eight exclude donors after one postpartum year. In a recent paper, Perrin et al. (2016) cited the lack of data on human milk composition beyond the first postpartum year and set out to describe longitudinal changes in composition during the second postpartum year with the goal of assisting in the development of evidence-based guidelines for human milk banks.¹

The research team examined macronutrients (total protein, total fat and lactose), bioactive proteins (lactoferrin, lysozyme and immunoglobulin A [IgA]), key minerals (calcium, zinc and iron), minerals associated with mammary gland involution (sodium and potassium) and human milk oligosaccharides linked to immunity and the gastrointestinal microbiome.

The research team recruited participants using a Facebook parenting group, ultimately engaging 19 participants who successfully provided monthly milk samples over the course of six months (11 months through 17 months postpartum), for a total of 131 longitudinal samples. For comparison, the researchers acquired 33 unpasteurized, pooled human milk samples from Mothers’ Milk Bank in San Jose, CA, representing 51 donors at a median lactation stage of four months.

Overall, the research team reports a significant increase in total protein, lactoferrin, lysozyme, IgA, sodium and total HMOS in the later samples, as well as a significant decrease in calcium and zinc for the same group. They found no longitudinal change for lactose, total fat, potassium or iron. Interestingly, they found that variability related most significantly to subject-effect for all nutrients rather than time-effect. This means that individual variations between donors are much more significant than time-based variations and that pooling strategies may mediate this variability.

Table 1. Comparison of longitudinal milk samples with pooled milk bank samples

	Longitudinal milk samples	Pooled milk bank samples
Protein (g/dl)*	1.7	1.5
Lactose (g/dl)	5.7	5.6
Fat (%)	4.1	3.5
Lactoferrin (mg/dl)*	210	140
Lysozyme (units/ml)*	68,000	31,000
IgA (mg/dl)*	23	17
Total HMOS (mg/ml)*	8.2	9.3
Total K (μg/ml)	370	390
Total Na (μg/ml)	76	83
Total Ca (μg/ml)*	190	220
Total Fe (ng/ml)	190	230
Total Zn (ng/ml)*	540	1200
NaK	0.21	0.21

* Significant changes indicated by italics.

Source: Perrin et al., 2016.

Perrin et al. suggest that ending early exclusion of milk donors makes sense, given the general stability or increasing concentrations of the macronutrients and bioactive factors studied. Accepting donations from second-year donors who breastfeed or express milk three or four times per day would benefit milk banks by both increasing overall supply and improving the quality of pooled milk (specifically total protein, lactoferrin, IgA and lysozyme content). They indicate that milk banks might consider mineral fortification since they observed small decreases in zinc and calcium in the later samples. Given that less than 50% of American NICUs offer donor milk despite its clear benefit to medically fragile neonates, their findings could significantly increase the supply of human breast milk available for medical institutions serving the most vulnerable infants.

Reference
1. Perrin, M.T., et al. (2016) “A longitudinal study of human milk composition in the second year postpartum: Implications for human milk banking,” Maternal & Child Nutrition, doi: 10.1111/mcn.12239 [Epub ahead of print].