The Macronutrient Contents of Donor Human Milk Were Not Impaired After 6 Months of Lactation

The aim of this study was to determine the energy and macronutrient contents in donor human milk longitudinally by time since delivery.

This prospective observational study was conducted in two Norwegian human milk banks from July 2018 to March 2022. The milk donors provided morning and evening samples of expressed milk once monthly until they stopped lactating. We used mid-infrared human milk analysers to measure the macronutrient contents. Changes by time were studied in paired t-tests and mixed regression models.

We analysed 446 samples of milk from 34 mothers. The mean energy content was 80 at 1-6 months versus 85 kcal/100 mL at 7-12 months of lactation (p = 0.03). Corresponding figures for fat, carbohydrates and protein were 4.7 versus 5.2 g/100 mL (p = 0.03), 8.3 versus 8.1 g/100 mL (p = 0.08) and 0.86 versus 0.91 g/100 mL (p = 0.16), respectively. The protein contents initially decreased, followed by a gradual increase after 6 months. The variations within and between mothers were much larger than the observed changes by time.

The macronutrient content of donor human milk was not impaired after 6 months of lactation. Common milk bank practices of restricting milk donation to the first months of lactation appear unnecessary.