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. 2025 Apr 17;110(3):248-252.
doi: 10.1136/archdischild-2024-327319.

Macronutrient concentrations in human milk beyond the first half year of lactation: a cohort study

Jacqueline Muts  1   2 , Juliette I A Lukowski  3 , Jos W R Twisk  4 , Anne Schoonderwoerd  5 , Johannes B van Goudoever  3   2   5 , Britt J van Keulen  3   2 , Chris H P Van Den Akker  2   5   6
Affiliations

Macronutrient concentrations in human milk beyond the first half year of lactation: a cohort study

Jacqueline Muts et al. Arch Dis Child Fetal Neonatal Ed. .

Abstract

Objective: Human milk composition is dynamic. While extensive research has focused on its macronutrient concentrations during the first 6 months of lactation, limited research exists for extended lactation periods. This study aims to examine the nutritional composition of human milk during these longer lactation phases.

Design: A retrospective longitudinal cohort study performed within the National Dutch Human Milk Bank.

Participants: We selected donors who had provided milk donations at least once after the 6-month postpartum mark.

Main outcome measures: The Miris Human Milk Analyser was used to analyse macronutrient concentrations in the milk samples. Linear mixed models were used for longitudinal analysis of these concentrations, factoring in time variables established for six sequential lactation periods.

Results: We analysed 820 milk samples from 86 women, collected between 5 weeks and 28 months postpartum. Initially, milk protein concentrations dropped over the first 8 months of lactation (diff = -0.19 g/dL, p<0.001) and stabilised between 8 and 18 months before increasing again by 0.21 (95% CI 0.06-0.21) g/dL. Carbohydrate concentrations remained steady throughout the study period. Fat concentrations were stable for the first 8 months but saw an increase afterwards. Post 18 months, the fat content saw a rise of 1.90 (95% CI 1.59-2.21) g/dL. The caloric density mirrored the pattern of the fat concentrations.

Conclusion: The nutritional content of human milk does not decrease after 6 months of lactation. Therefore, human milk banks may accept donations from mothers up to 2 years post-birth.

Keywords: Infant Development; Intensive Care Units, Neonatal; Neonatology.

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Conflict of interest statement

Competing interests: JM, JIAL, JWRT, BJvK, AS: All report no conflict of interest. JBvG: Member of the Dutch National Health Institute and founder and director of the Dutch National Human Milk Bank. CHPVDA: Reports receipt of speakers and consultancy honoraria from Nestlé Nutrition Institute, Nutricia Early Life Nutrition and Baxter.

Figures

Figure 1
Figure 1. A–D Longitudinal macronutrient concentrations in months postpartum in donated human milk samples (n=86 donors, N=820 samples). A: crude protein concentration; B: carbohydrate concentration; C: fat concentration; D: energy content. The grid lines on the x-axis indicate the lactation periods defined in this study and used for the statistical analyses. Bold trendlines represent the average values.
See this image and copyright information in PMC

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