Human Milk Research Research Articles

Human Milk-The Biofluid That Nourishes Infants from the First Day of Life.

Human milk is a biofluid with a unique composition among mammalian milks. Besides this milk's major components, its bioactive compounds, like hormones, immune factors, and oligosaccharides, are unique and important for infant growth and development. The best form of nutrition for term and preterm infants is the mother's own milk. However, in the absence of the mother's own milk, donor milk should be made available. Milk banks support neonatal intensive care units by providing preterm infants with human milk that generally has reasonable nutritive value for this sensitive population. However, neither mother's own milk nor donor milk has sufficient energy content for the growth of preterm babies, so adequate human milk supplementation is crucial for their progress. Due to the different characteristics of human breast milk, as well as ubiquitous environmental pollutants, such as microplastics, new methods are required for monitoring the quality and characteristics of human milk, which will lay a solid foundation for the further development and progress of human milk research.

Influence of an Early Human Milk Diet on the Duration of Parenteral Nutrition and Incidence of Late-Onset Sepsis in Very Low Birthweight (VLBW) Infants: A Systematic Review.

Introduction: Human milk is the preferred source of enteral nutrition for very low birthweight (VLBW) infants, and it possibly decreases dependence on parenteral nutrition (PN) and reduces incidence of late-onset sepsis (LOS). No systematic review to date has specifically addressed the value of early versus late introduction of human milk diet (HMD) on duration of PN and incidence of LOS among VLBW infants. Objective: To review the evidence for an early versus late introduction of HMD on duration of PN and incidence of LOS in VLBW infants. Method: Preferred reporting items for systematic reviews and meta-analysis-guided search of EMBASE and PubMed/Medline databases was conducted for this systematic review using phrases addressing population, intervention, comparator, and outcome framework to identify articles published over the past two decades without language restrictions. Full-text articles (both observational and randomized) that studied an early versus late initiation of HMD were included. Mean difference (MD) and relative risk (RR) with 95% confidence intervals (CIs) were calculated for PN and LOS. Quality of evidence was analyzed using UK National Service Framework and the risk-of-bias was assessed using Robvis®. Results: One randomized controlled trial (RCT) and two observational studies (two English and one Chinese) recruited 474 VLBW infants (455 analyzed). Among an intrauterine growth-restricted cohort enrolled in the RCT (n = 72), early HMD resulted in statistically significant reduction in PN dependence. However, no statistically significant difference was found in LOS. Two observational studies found similar reductions in PN duration and LOS incidence among the early HMD cohort. One observational study reported significant PN reduction; however, the incidence of LOS did not reach statistical significance in either case. Conclusion: An early HMD may reduce the duration of PN for a growth-restricted VLBW cohort. Observational studies suggesting reduced PN and LOS from early HMD endorse the need for bioactivity-focused human milk research. Variations in feeding guidelines among VLBW infants have the potential to influence neonatal outcomes significantly.

Access to and interest in human milk research opportunities among Black pregnant and postpartum people.

Concerns exist regarding biomedical research participation in marginalized and historically disadvantaged communities. The purpose of this study was to understand critical barriers to participation in human milk research from the perspective of Black pregnant and postpartum people. A national sample of Black pregnant and postpartum people (n = 104) was recruited to complete a cross-sectional online survey informed by the Life Course Perspective. Survey questions assessed research experiences and preferences, particularly related to human milk research, knowledge of historical events/policies targeting Black communities, and demographic characteristics. A socio-economic composite score was calculated as an indicator of socio-economic advantage. Survey data were summarized descriptively and potential correlates of research engagement were evaluated. Most (69%, n = 71) respondents reported previous participation in a research study, yet only 8 (8%) reported ever being asked to participate in a breastfeeding/chestfeeding or human milk study, and one respondent was unsure. Despite so few having been asked, 59% (n = 61) of respondents indicated they would donate breast/human milk to research if asked. Respondent characteristics associated with prior research participation included having greater socio-economic advantage (p = 0.027) and greater knowledge of discriminatory historical events/policies (p < 0.001). In contrast, the only respondent characteristic associated with willingness to donate human milk to research was younger age (p = 0.002). Our findings suggest that Black pregnant and postpartum people are interested in biomedical research, specifically human milk and lactation research. However, greater intentionality and targeted recruitment of this underrepresented population is needed to increase diversity among human milk and lactation study samples. Structural and community-based interventions, informed by community members, are needed to address concerns and improve participant engagement.

Consistency and Variability of the Human Milk Oligosaccharide Profile in Repeat Pregnancies.

Human milk oligosaccharides (HMOs) are a set of complex carbohydrates and the third largest solid component of human milk, after lactose and lipids. To date, over 150 HMOs have been identified and the diversity of structures produced by lactating women is influenced by maternal genetics as well as other maternal, infant, and environmental factors. While the concentrations of individual HMOs have been shown to vary between individuals and throughout the course of lactation, the variability of HMO concentration profiles following different pregnancies occurring in the same woman is presently unknown. As such, the objective of this study was to compare HMO concentrations in human milk samples provided by the same women (n = 34) following repeat pregnancies. We leveraged existing human milk samples and metadata from the UC San Diego Human Milk Research Biorepository (HMB) and measured the concentrations of the 19 most abundant HMOs using high-performance liquid chromatography with fluorescence detection (HPLC-FL). By assessing dissimilarities in HMO concentration profiles, as well as concentration trends in individual structures between pregnancies of each participant, we discovered that HMO profiles largely follow a highly personalized and predictable trajectory following different pregnancies irrespective of non-genetic influences. In conclusion, this is the first study to assess the interactions between parity and time following delivery on variations in HMO compositions.

Cannabidiol Exposure Through Maternal Marijuana Use: Predictions in Breastfed Infants.

Knowledge about exposure to cannabidiol (CBD) in breastfed infants can provide an improved understanding of potential risk. The aim was to predict CBD exposure in breastfed infants from mothers taking CBD and CBD-containing products. Cannabidiol concentrations in milk previously attained from data collected through an existing human milk research biorepository were used to simulate infant doses and identify subgroups. A developed pediatric physiologically based pharmacokinetic model produced virtual breastfed infants administered the simulated CBD doses. Predicted breastfed infant exposures and upper area under the curve ratios were compared to the lowest therapeutic dose for approved indications in children. The existing human milk research biorepository contained 200 samples from 181 unique breastfeeding mothers for whom self-reported administration data and CBD concentrations had previously been measured. Samples that were above the lower limit of quantification with only one maternal administration typerevealed that administration type, i.e., joint/blunt or edible versus oil or pipe, resulted in significantly different subgroups in terms of milk concentrations. Resulting simulated infant doses (ng/kg) were described by lognormal distributions with geometric means and geometric standard deviations: 0.61 ± 2.41 all concentrations, 0.10 ± 0.37 joint/blunt or edible, and 2.23 ± 8.15 oil or pipe. Doses administered to breastfed infants had exposures magnitudes lower than exposures in children aged 4-11 years administered the lowest therapeutic dose for approved indications, and low upper area under the curve ratios. Based on real-world use, breastfeeding infants are predicted to receive very small exposures of CBD through milk. Studies examining adverse reactions will provide further insight into potential risk.

Persistent organic pollutants in Croatian breast milk: An overview of pollutant levels and infant health risk assessment from 1976 to the present.

This review article summarizes our research of persistent organic pollutants (POPs) in human milk from Croatian mothers over the last few decades. Our studies make up the bulk of all POPs research in human milk in Croatia and show a state-of-the art in the research area. The first investigations were made in 1970`s. Aim of our review article is to document the comprehensive results over several decades as the best tool to: 1.) contribute to understanding of POPs and their potential health risks, 2.) evaluate effectiveness of legislative bans and restrictions on human exposure to POPs in Croatia, and 3.) to suggest further actions. In our review we discuss: 1.) Human milk between 2011 and 2014 - evaluation of interrelations of organochlorine pesticides (OCP) and polychlorinated biphenyls (PCB) in human milk and their association with the mother's age and parity using artificial intelligence methods; and our yet unpublished research data on health risks for infants assessed through daily PCB and OCP intake. 2.) Time trends of PCB and OCP in human milk between 1976 and 2014.3.) polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofuran (PCDD/F) in human milk in 2000., and yet unpublished data on PCDD/F and polybrominated diphenyl ethers (PBDE) in 2014.

The impact of thawing duration on leptin and adiponectin levels in frozen human milk samples.

Measurements of hormone concentrations in human milk from understudied populations across the world is of growing scientific interest. Due to limited access to suitable laboratory facilities at many research sites, human milk samples are often shipped frozen to distant laboratories for analysis. Shipping and handling exposes samples to the risk of thawing and degradation as the results of delays, mishandling, or other unforeseen circumstances. Similar degradation risk factors are well known in serum samples. However, the vulnerability of hormone degradation in human milk to thawing during transportation is largely unexplored. Leptin and adiponectin are of particular importance due to their roles in feeding behavior and metabolism in infants, hence our focus on these two hormones. In addition, leptin and adiponectin have been shown to be vulnerable to pasteurization temperature degradation in human milk samples. We tested the degradation of human milk metabolic hormones - leptin and adiponectin - in a controlled environment in response to a variety of freeze/thaw conditions that are reflective of potential temperature fluctuations during transportation. Human milk samples were experimentally subjected to thaw durations ranging from 4 to 16 h and assayed for hormonal levels to observe changes from baseline. Samples were also subjected to two additional experimental conditions, re-freezing after an extended period outside freezers or remaining thawed with additional ice packs, to investigate the impact of common transportation conditions. We found the assayed levels of leptin were not significantly impacted by an extended thaw cycle of 16 h. However, leptin levels were impacted by the extended period of 40 h outside of the freezer. Adiponectin showed a decrease in concentration percentage after the initial 16-h thaw period, but the increased degradation between 0-16 h and 16-40 h was not as severe as that seen in the leptin samples. The results of this experiment can be used to inform hormone measurement consistency given different thawing lengths or freezing conditions during transportation. Additionally, this research informs decisions regarding transportation, storage/handling, and data analysis in human milk research.

Editorial introductions.

Editorial introductions.

An equitable, community-engaged translational framework for science in human lactation and infant feeding—a report from “Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN)” Working Group 5

Human milk is the ideal source of nutrition for most infants, but significant gaps remain in our understanding of human milk biology. As part of addressing these gaps, the Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) Project Working Groups 1–4 interrogated the state of knowledge regarding the infant–human milk–lactating parent triad. However, to optimize the impact of newly generated knowledge across all stages of human milk research, the need remained for a translational research framework specific to the field. Thus, with inspiration from the simplified environmental sciences framework of Kaufman and Curl, Working Group 5 of the BEGIN Project developed a translational framework for science in human lactation and infant feeding, which includes 5 nonlinear, interconnected translational stages, T1: Discovery; T2: Human health implications; T3: Clinical and public health implications; T4: Implementation; and T5: Impact. The framework is accompanied by 6 overarching principles: 1) Research spans the translational continuum in a nonlinear, nonhierarchical manner; 2) Projects engage interdisciplinary teams in continuous collaboration and cross talk; 3) Priorities and study designs incorporate a diverse range of contextual factors; 4) Research teams include community stakeholders from the outset through purposeful, ethical, and equitable engagement; 5) Research designs and conceptual models incorporate respectful care for the birthing parent and address implications for the lactating parent; 6) Research implications for real-world settings account for contextual factors surrounding the feeding of human milk, including exclusivity and mode of feeding. To demonstrate application of the presented translational research framework and its overarching principles, 6 case studies are included, each illustrating research gaps across all stages of the framework. Applying a translational framework approach to addressing gaps in the science of human milk feeding is an important step toward the aligned goals of optimizing infant feeding across diverse contexts as well as optimizing health for all.

The Human Milk Metabolome: A Scoping Literature Review.

Human milk is a complex source of nutrition and other bioactives that protects infants from disease, holding a lifetime of beneficial effects. The field of metabolomics provides a robust platform through which we can better understand human milk at a level rarely examined. To Identify, describe, synthesize, and critically analyze the literature within the past 5 years related to the human milk metabolome. We conducted a scoping literature review and quality analysis of the recent science reflecting untargeted metabolomic approaches to examining human milk. We searched six databases using the terms "breast milk," "metabolome," "metabolite," and "human milk," Out of more than 1,069 abstracts, we screened and identified 22 articles that met our inclusion criteria. We extracted data related to the study author, geographic location, research design, analyses, platform used, and results. We also extracted data related to human milk research activities, including collection protocol, infant/maternal considerations, and time. Selected studies focused on a variety of phenotypes, including maternal and infant disease. Investigators used varying approaches to evaluate the metabolome, and differing milk collection protocols were observed. The human milk metabolome is informed by many factors-which may contribute to infant health outcomes-that have resulted in disparate milk metabolomic profiles. Standardized milk collection and storage procedures should be implemented to minimize degradation. Investigators may use our findings to develop research questions that test a targeted metabolomic approach.

The Association Between Adverse and Positive Childhood Experiences and Marijuana Use During Lactation.

Background: Adverse childhood experiences (ACEs) are associated with substance use later in life, including marijuana use. It is unknown whether these behaviors extend to lactating women. Our objective was to examine the association between childhood ACE and marijuana use in lactating individuals and determine whether positive childhood experiences (PCEs) modified this association. Methods: This study included 617 lactating individuals from the UC San Diego Human Milk Research Biorepository enrolled from 2015 to 2020. ACE and PCE histories were assessed by the Positive and Adverse Childhood Experiences questionnaire. Past 2-week marijuana use was self-reported at enrollment. Multivariable log-linear regressions were used to calculate adjusted risk ratios (aRRs) and 95% confidence intervals (CIs) for ACE history and marijuana use, and to assess modification by PCE. Results: Marijuana use during lactation was higher among individuals who reported three or more ACEs (aRR = 2.58, 95% CI = 1.23-5.44), household dysfunction (aRR = 3.08, 95% CI = 1.17-8.10), sexual abuse (aRR = 2.25, 95% CI = 1.08-4.68), or physical abuse (aRR = 2.10, 95% CI = 1.02-4.13). There was no association between emotional abuse and marijuana use during lactation. There was no effect modification by PCEs. Conclusion: Higher ACE frequency, and specifically history of household dysfunction, physical abuse, or sexual abuse increased risk for marijuana use during lactation. Because of marijuana's potential adverse effects on the infant through human milk, postpartum ACE screening is warranted.

Human Milk Oligosaccharides, Important Milk Bioactives for Child Health: A Perspective.

Human milk contains all nutritive and bioactive compounds to give infants the best possible start in life. Human milk bioactives cover a broad range of components, including immune cells, antimicrobial proteins, microbes, and human milk oligosaccharides (HMOs). Over the last decade, HMOs have gained special attention as their industrial production has allowed the study of their structure-function relation in reductionist experimental setups. This has shed light on how HMOs steer microbiome and immune system development in early life but also how HMOs affect infant health (e.g., antibiotic use, respiratory tract infections). We are on the verge of a new era where we can examine human milk as a complex biological system. This allows not only study of the mode of action and causality of individual human milk components but also investigation of synergistic effects that might exist between different bioactives. This new wave in human milk research is largely fueled by significant advances in analytical tools in the field of systems biology and network analysis. It will be exciting to explore how human milk composition is affected by different factors, how different human milk compounds work together, and how this influences healthy infant development.

Past, Present and Future of Human Milk Research.

Human milk is the best source of infant nutrition and is recognized as a biological fluid vital for optimal growth and development. It has established short- and long-term benefits to infants and mothers. Sapiens' milk has coevolved with mammalian species for millennia which has resulted in this remarkable secretory product of nutrient-rich milk. The nutritional composition and nonnutritive bioactive factors in human milk are uniquely appropriate for the infant, which provides survival and healthy development. Research over the past 2-3 decades focused on increasing the understanding about the composition of human milk and different factors that influence the composition such as stage of lactation, impact of maternal diet, geographical location, gestational age at infant birth, and circadian rhythm. Presently, collaborative efforts are ongoing in communicating the clinical advantages of human milk composition in relation to public health. Different groups are also working on the establishment of reference in the form of databases using reference and growth standard methodology. Toward the future, with computational and modeling methods, the next stage is to understand human milk as a biological system. Cellular agriculture is also the next exciting field of human milk research.

The Prevalence of Nonserious Events in a Cohort of Breastfed Infants.

Introduction: Data on baseline rates of nonserious events in breastfed infants in the general population are sparse. This results in difficulty determining if there is an increase in infant nonserious events potentially due to prescription medication exposure through human milk. In this study, we determined the prevalence of nonserious events in infants consuming human milk whose mothers reported no exposure to any prescription medications, tobacco, or recreational drugs in the previous 14 days. Materials and Methods: Between August 2014 and December 2019, 487 breastfeeding mothers without any recent exposure to prescription medications, tobacco, or recreational drugs enrolled in the Human Milk Research Biorepository at the University of California, San Diego. Participants completed a semistructured telephone interview with trained research staff and provided information on maternal and child health, breastfeeding habits, recent medication, and lifestyle exposures, and completed a standard checklist of infant adverse reactions. Results: We found 131 (44.1%) participants reported one or more infant nonserious adverse events in the past 14 days at the time of their study interview. The most commonly reported nonserious events were rash (12.1%), irritability (9.4%), constipation (7.8%), poor sleep (7.1%), and fever (6.3%). Conclusions: These baseline frequencies provide a benchmark for rates of recent nonserious events in breastfed infants in the general population. These data can be used as a reference point for studies that examine adverse events in breastfed infants following maternal use of prescription medications or exposures due to other lifestyle habits such as tobacco or other substances. Clinical Trial Registration Number: NCT05553743.

Point-of-care human milk testing for maternal secretor status

We present an electrochemical impedimetric-based biosensor for monitoring the variation in human milk oligosaccharide (HMO) composition. 2′-Fucosyllactose (2’FL) is an HMO associated with infant growth, cognitive development, and protection from infectious diarrhea, one of the major causes of infant death worldwide. Due to genetic variation, the milk of some women (non-secretors) contains no or very little 2′FL with potential implications for infant health and development. However, there is currently no technology to analyze the presence and concentration of HMOs in human milk at the point-of-care (POC). The lack of such technology represents a major impediment to advancing human milk research and improving maternal-infant health. Towards this unmet need, we report an impedimetric assay for HMOs with an α-1,2 linkage, the most abundant of which is 2′FL. The sensor uses a lectin for affinity, specifically Ulex europaeusagglutininI (UEA), with electrochemical readout. In spiked studies, the sensor exhibited a high degree of linearity (R2 = 0.991) over 0.5 to 3.0 μM with a 330-nM detection limit. The sensor performance was clinically validated using banked human milk samples and correctly identified all secretor vs. non-secretor samples. Furthermore, despite the short 35-min assay time and low sample volume (25 μL), the assay was highly correlated with HPLC measurements. This bedside human milk testing assay enables POC, “sample-to-answer” quantitative HMO measurement, and will be a valuable tool to assess milk composition.Graphical abstract

Maternal and Child Outcomes Reported by Breastfeeding Women Following Messenger RNA COVID-19 Vaccination.

Background: In December 2020, two novel messenger RNA (mRNA) vaccines for severe acute respiratory syndrome coronavirus-2 received emergency use authorization from the U.S. Food and Drug Administration; however, the early trials excluded lactating women. Methods: Breastfeeding women residing in the United States who received either of the two mRNA vaccines were enrolled into the Mommy's Milk Human Milk Research Biorepository at the University of California, San Diego. From December 14, 2020 to February 1, 2021, 180 women who received two doses of either mRNA vaccine were recruited into the study. Results: Similar proportions of women reported any one or more symptoms following vaccination with either mRNA vaccine. In addition, the frequency by specific type of symptom did not differ by brand. However, following the second dose of vaccine, women who received the Moderna brand were significantly more likely to report symptoms. A small proportion of women following the first dose of either vaccine brand reported a reduction in milk supply, and significantly, more women reported a reduction in milk supply following the second dose of Moderna. Few infant events were reported for either vaccine brand following either dose, and no serious adverse events were reported. Conclusions: These data are reassuring regarding the safety of vaccination in breastfeeding women and their breastfed children with either of the mRNA COVID-19 vaccines.

Human Milk and Brain Development in Infants

Human milk is considered the most advantageous source of nourishment for infants. Even though there is no ideal composition of human milk, it still contains a unique combination of components that contribute to brain development. The aim of this review is to provide an overview on the possible correlation of human milk with the neurodevelopment of infants, with a special emphasis on myelination and epigenetic modifications. Research in human milk is a rapidly expanding field and cutting-edge technologies might contribute to identify specific mechanisms underlying the beneficial effects on human milk on neurodevelopment.

Editorial introductions

Editorial introductions

The importance of infants' lipid intake in human milk research.

Human milk lipids are among the many nutrients delivered to the infant, providing >50% of the infant's calorie intake. These lipids are highly complex and variable, and bioactive, contributing to infant growth, development, and health. The lipid concentration of milk samples is often measured in human cohorts; however, few studies measure infant intake of milk. Intake is important because it considers the variability of both lipid concentration and infants' consumed volume of milk. Measurement of infants' lipid intake in exclusively breastfeeding infants requires 3 main considerations: human milk sampling protocol (ie, the collection of representative samples); measurement of the infant milk intake, because volume varies widely between infants; and appropriate analytical laboratory methods. The purpose of this review was to provide an overview of existing methodology and demonstrate the importance of measuring infants' lipid intake to understand the impact that human milk lipids have on infant outcomes.

Longitudinal Changes in Crude Protein and Amino Acids in Human Milk in Chinese Population: A Systematic Review.

More than 20% of the world population live in China, which has made significant achievement in human milk research. Part of the data that were published in Chinese were, however, unavailable to non-Chinese speakers. There was also no comprehensive overview of crude protein and amino acid levels in human milk in Chinese population. This systematic review aimed to compile the data on human milk crude protein and amino acid levels in Chinese population. After searching for and screening original research articles in both English and Chinese, 23 published from 1987 to 2019 were identified (18 in Chinese and 5 in English). The data were pooled into 9 defined lactation stages. Crude protein and amino acids (protein bound plus nonprotein bound) concentrations gradually decreased during the first 60 postpartum days and remained relatively static thereafter. The concentrations and dynamic change of crude protein and amino acids were similar to those in other populations. By contrast, the longitudinal changes in free amino acids (nonprotein bound) were less clear due to the limited data available. Several common weaknesses were identified in these studies. Our study represented the most comprehensive overview on crude protein and amino acid concentrations in human milk in Chinese population, and enhanced the knowledge of protein and amino acid intakes and requirements by Chinese infants.