Cytokines and appetite-regulating hormones in human milk and associations with infant growth across four sites in a longitudinal cohort: The Mothers, Infants and Lactation Quality Study

Authors: CHRISTENSEN, SOPHIE - University Of Copenhagen; LEWIS, JACK - University Of Copenhagen; FRØKIÆR, HANNE - University Of Copenhagen; JOHNSEN, PETER - University Of Copenhagen; PEERSON, JANET - Eg Consulting (SELF-EMPLOYED); TAN, XIUPING (JENNY) - University Of California, Davis; Shahab-Ferdows, Setareh; HAMPEL, DANIELA - University Of California, Davis; ISLAM, MUNIRUL - International Centre For Diarrhoeal Disease Research; KAC, GILBERTO - Federal University - Brazil; DE BARROS MUCCI, DANIELA - Federal University - Brazil; FIGUEIREDO, AMANDA - Federal University - Brazil; MOORE, SOPHIE - King'S College; MØLGAARD, CHRISTIAN - University Of Copenhagen; Allen, Lindsay; MICHAELSEN, KIM - University Of Copenhagen

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2025
Publication Date: 5/8/2025
Citation: Christensen, S.H., Lewis, J.I., Frøkiær, H., Johnsen, P.R., Peerson, J., Tan, X., Shahab-Ferdows, S., Hampel, D., Islam, M., Kac, G., de Barros Mucci, D., Figueiredo, A.C., Moore, S.E., Mølgaard, C., Allen, L.H., Michaelsen, K.F. 2025. Cytokines and appetite-regulating hormones in human milk and associations with infant growth across four sites in a longitudinal cohort: The Mothers, Infants and Lactation Quality Study. PLOS ONE. 20(5). Article e0323204. https://doi.org/10.1371/journal.pone.0323204.
DOI: https://doi.org/10.1371/journal.pone.0323204

Interpretive Summary: In developing countries, mothers and their infants are subjected to environmental factors that can increase the occurrence of infectious diseases and could impact the human milk (HM) cytokine profile. HM hormones are thought to affect appetite-regulation and growth. Hence, we aim to compare cytokines and appetite-regulating hormones (ARHs) in HM of mothers from four populations exposed to different environmental factors and investigate the association between these HM markers and infant growth. The sample size of 820 well-characterized mother-infant dyads from four countries uniquely enable us to compare associations between HM bioactive compounds and infant growth across lactation in a global perspective. Our results indicate that different environmental exposures, and the subsequent stimulus of the maternal immune response, are reflected in the HM cytokine profile, and thus, possibly reflect the immune stimulatory environment of the offspring.

Technical Abstract: In low- and middle-income countries, mother-infant dyads are exposed to environmental factors which increase the risk of infectious diseases and may influence the cytokine profile of human milk (HM). Hormones in HM have further been proposed to influence appetite-regulation and possibly growth in exclusively breastfed infants. Our objective was to compare cytokines and appetite-regulating hormones (ARH) in HM of mothers exposed to different health and nutrition environments, and investigate the association between these HM markers and infant growth. 820 mother-infant dyads participating in the Mothers, Infants and Lactation Quality (MILQ) Study from Bangladesh (BD, n=245), Brazil (BR, n=194), Denmark (DK, n=194) and from The Gambia (GM, n=187) were included in the present analysis. HM samples were collected between 1-3.5 months postpartum and analyzed for the cytokines Tumor-necrosis factor (TNF)-a, Interferon (IFN)-', Interleukin(IL)-1ß, IL-4, IL-6, IL-8, IL-10, IL-33, and the ARHs insulin, leptin and adiponectin. Infant growth was measured twice between 1.0-5.99 months postpartum and Z-scores were calculated according to WHO Growth references. Analysis of Covariance was used to compare logarithmic means of HM markers between the four populations . Linear regression analysis was applied to investigate the associations between HM markers and infant growth Z-scores. Differences in logarithmic means between the four study sites were found for all cytokines and ARHs in HM after adjustment for possible explanatory variables. Lowest levels of most HM cytokines were found in BD, whereas HM levels of IL-33 and adiponectin were different in all four populations. Most cytokines were inversely associated with weight-for-age and weight-for-length Z-scores (WAZ, WLZ) in GM only. We showed significant differences in HM composition of cytokines and ARHs between the four countries of the MILQ cohort. Highest levels of cytokines typically related to increased risk of atopic diseases were found in DK, while levels of ARHs were highest in BR and lowest in BD. Furthermore, higher levels of most HM cytokines were associated with declining WAZ and WLZ up to six months postpartum in GM only. The results likely reflect different environmental exposures in the four countries, which may affect growth in GM.