Microbiota Composition of Breast Milk from Women of Different Ethnicity from the Manawatu-Wanganui Region of New Zealand

The association between maternal body mass index and breast milk composition: a systematic review

CONTEXT

Breast milk composition is influenced by many factors, ranging from maternal nutritional status to infant sex. Previous studies have explored the relationship between maternal body mass index (BMI) and breast milk composition; however, the findings have been inconsistent and controversial.

OBJECTIVE

To systematically review the evidence on the association of maternal weight and BMI with breast milk composition.

DATA SOURCES

The PubMed and Scopus databases were searched up to May 3, 2023, using the following search strategy: ("maternal weight" OR "maternal BMI" OR "mother's weight" OR "mother's BMI") AND ("maternal milk" OR "human milk" OR "breast milk").

DATA EXTRACTION

A total of 83 publications, involving data from more than 11 310 lactating women, were identified. All extracted data were compiled, compared, and critically analyzed.

DATA ANALYSIS

Overall, maternal BMI was associated with higher levels of leptin and insulin, and the ratio of omega-6 to omega-3 polyunsaturated fatty acids in breast milk. However, no conclusive associations were found between maternal BMI and the levels of energy, macronutrients, micronutrients, and other components of breast milk.

CONCLUSIONS

This systematic review provides robust evidence supporting a positive correlation between maternal BMI and breast milk concentrations of leptin, insulin, and the omega-6 to omega-3 polyunsaturated fatty acid ratio. Nevertheless, disparities in findings are noticeable for other constituents of breast milk. To comprehensively grasp the influence of maternal weight and BMI on breast milk composition, further research endeavors are imperative.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42023458667.

The Impact of the Human Milk Microbiota in the Prevention of Disease and Infant Health

Background: Human milk is recognized as an ideal food for newborns and infants owing to the presence of various nutritive factors, including healthy bacteria. Aim/Objective: This review aimed to understand the effects of human milk microbiota in both the prevention of disease and the health of infants. Methods: Data were obtained from PubMed, Scopus, Web of Science, clinical trial registries, Dergipark, and Türk Atıf Dizini up to February 2023 without language restrictions. Results: It is considered that the first human milk microbiota ingested by the newborn creates the initial microbiome of the gut system, which in turn influences the development and maturation of immunity. Bacteria present in human milk modulate the anti-inflammatory response by releasing certain cytokines, protecting the newborn against certain infections. Therefore, certain bacterial strains isolated from human milk could serve as potential probiotics for various therapeutic applications. Conclusions: In this review, the origin and significance of human milk bacteria have been highlighted along with certain factors influencing the composition of human milk microbiota. In addition, it also summarizes the health benefits of human milk as a protective agent against certain diseases and ailments.

Maternal Gut Microbiota in the Postpartum Period: A Systematic Review

Studies have demonstrated the importance of the gut microbiota during pregnancy, and there is emerging literature on the postpartum maternal gut microbiota. The primary objective of this paper was to synthesize the literature on the postpartum gut microbiome composition and diversity measured in stool samples from healthy mothers of predominantly term infants. The secondary objectives were (1) to identify biological and environmental factors that influence postpartum maternal gut microbiota and (2) to assess health conditions and clinical intermediate measures associated with postpartum gut microbiota changes in all mothers. Electronic searches were conducted November 9, 2020 and updated July 25, 2021 without publication time limits on PubMed, Embase, CINHAL, Scopus, Cochrane Library, BioArchives, and OpenGrey.eu. Primary research on maternal gut microbiota in the postpartum (up to one year after childbirth) were eligible. Postpartum gut microbiota comparisons to pregnancy or non-pregnancy gut microbiota were of interest, therefore, studies examining these in addition to the postpartum were included. Studies were excluded if they were only conducted in animals, infants, pregnancy, or microbiome of other body locations (e.g., vaginal). Data extraction of microbial composition and diversity were completed and synthesized narratively. Studies were assessed for risk of bias. A total of 2512 articles were screened after deduplication and 27 were included in this review. Of the 27 included studies, 22 addressed the primary objective. Firmicutes was the predominant phylum in the early (<6 weeks) and late postpartum (6 weeks to 1 year). In early postpartum, Bacteroides was the predominant genus. Findings from longitudinal assessments of alpha and beta diversity from the early to the late postpartum varied. Nineteen of the 27 studies assessed biological and environmental factors influencing the postpartum gut microbial profile changes. Timing of delivery, probiotic supplementation, triclosan exposure, and certain diets influenced the postpartum gut microbiota. Regarding health conditions and intermediate clinical measures assessed in 8 studies; inflammatory bowel disease, postpartum depression, early-onset preeclampsia, gestational diabetes, excessive gestational weight gain, and anthropometric measures such as body mass index and waist-to-hip ratio were related to gut microbiota changes. There is limited data on the maternal postpartum gut microbiota and how it influences maternal health. We need to understand the postpartum maternal gut microbiome, establish how it differs from non-pregnancy and pregnancy states, and determine biological and environmental influencers. Future research of the gut microbiome's significance for the birthing parent in the postpartum could lead to a new understanding of how to improve maternal short and long-term health.

Maternal weight status and the composition of the human milk microbiome: A scoping review

The human milk microbiome is thought to partly contribute to the assembly of the infant gut microbiome, a microbial community with important implications for infant health and development. While obesity has well-established links with the adult gut microbiome, less is known about how it affects the human milk microbiome. In this scoping review, we synthesize the current literature on the microbial composition of human milk by maternal weight status, defined broadly as BMI (prepregnancy and postpartum) and gestational weight gain (GWG). This study followed the a priori protocol published in Prospero (registration #: CRD42020165633). We searched the following databases for studies reporting maternal weight status and a characterization of milk microbiota through culture-dependent and culture-independent methods: MEDLINE, Embase, Web of Science, CINAHL, and Scopus. After screening 6,365 studies, we found 20 longitudinal and cross-sectional studies investigating associations between maternal weight status and the composition of the milk microbiome. While some studies reported no associations, many others reported that women with a pre-pregnancy or postpartum BMI characterized as overweight or obese, or with excessive GWG, had higher abundances of the genus Staphylococcus, lower Bifidobacterium abundance, and lower alpha diversity (within-sample diversity). This review suggests that maternal weight status is minorly associated with the composition of the milk microbiome in various ways. We offer potential explanations for these findings, as well as suggestions for future research.

Food Insecurity and Maternal Diet Influence Human Milk Composition between the Infant's Birth and 6 Months after Birth in Central-Africa

Although the World Health Organization (WHO) and UNICEF recommend that infants should be exclusively breastfed for the first 6 months of life, evidence is scarce on how the mother’s undernourishment status at delivery and maternal dietary factors influence human milk (HM) composition during the first 6 months of life in regions with high food insecurity. The maternal undernourishment status at delivery, maternal diet, and HM nutrients were assessed among 46 women and their 48 vaginally born infants in Bangui at 1, 4, 11, 18, and 25 weeks after birth through 24-h recalls and food consumption questionnaires from December 2017 to June 2019 in the context of the "Mother-to-Infant TransmIssion of microbiota in Central-Africa" (MITICA) study. High food insecurity indexes during the follow-up were significantly associated with them having lower levels of many of the human milk oligosaccharides (HMOs) that were measured and with lower levels of retinol (aß-coef = −0.2, p value = 0.04), fatty acids (aß-coef = −7.2, p value = 0.03), and amino acids (aß-coef = −2121.0, p value < 0.001). On the contrary, women from food-insecure households displayed significantly higher levels of lactose in their HM (aß-coef = 3.3, p value = 0.02). In parallel, the consumption of meat, poultry, and fish was associated with higher HM levels of many of the HMOs that were measured, total amino acids (aß-coef = 5484.4, p value < 0.001), and with lower HM levels of lactose (aß-coef = −15.6, p value = 0.01). Food insecurity and maternal diet had a meaningful effect on HM composition with a possible impact being an infant undernourishment risk. Our results plead for consistent actions on food security as an effective manner to influence the nutritional content of HM and thereby, potentially improve infant survival and healthy growth.

Association between Maternal Characteristics and Immune Factors TGF-β1, TGF-β2, and IgA in Colostrum: An Exploratory Study in Japan

Colostrum is the first food for newborns and it contains various crucial immune factors. The concentrations of immune factors in breast milk may change depending on maternal characteristics such as body mass index, collection day, and age at first pregnancy. In this exploratory study, we investigated the association between TGF-β1, TGF-β2, and IgA in colostrum and rarely studied factors that affect breast milk components, including the use of labor-inducing medication, colostrum secretion, sex of newborns, breast or nipple problems, and nipple care. Breast milk samples were collected from 42 mothers and analyzed for TGF-β1, TGF-β2, and IgA. The results suggest that parity and mode of delivery may be correlated with the concentrations of immune factors in colostrum. However, we found no association between the immune factors in colostrum and the use of labor-inducing medications, colostrum secretion, sex of newborns, breast or nipple problems, and nipple care. These findings have some implications for further analysis of the effects of immune factors in breast milk on the prognosis of allergies in children.

The human milk microbiome aligns with lactation stage and not birth mode

We analysed the human milk microbiome in a cohort of 80 lactating women and followed the dynamics in taxa over the course of lactation from birth to 6 months. Two hundred and thirty one milk samples were collected from full-term lactating women at 1, 4, 8 and 24 weeks following birth and analysed for microbiota composition using 16S rRNA sequencing. A significant decrease in milk microbiota diversity was observed throughout the first 6 months of lactation, with the greatest difference seen between week 8 and week 24. Nine genera predominated in milk over lactation from week 1 to week 24, comprising of Staphylococcus, Streptococcus, Pseudomonas, Acinetobacter, Bifidobacterium, Mesorhizobium, Brevundimonas, Flavobacterium, and Rhodococcus; however, fluctuations in these core genera were apparent over time. There was a significant effect of stage of lactation on the microbiome, while no effect of birth mode, infant sex and maternal BMI was observed throughout lactation. Streptococcus had the highest mean relative abundance at week 1 and 24 (17.3% and 24% respectively), whereas Pseudomonas predominated at week 4 (22%) and week 8 (19%). Bifidobacterium and Lactobacillus had the highest mean relative abundance at week 4 (5% and 1.4% respectively), and occurred at a relative abundance of ≤ 1% at all other time points. A decrease in milk microbiota diversity throughout lactation was also observed. This study concluded that lactation stage was the primary driving factor in milk microbiota compositional changes over lactation from birth to 6 months, while mode of delivery was not a factor driving compositional changes throughout human lactation.

Breastfeeding Practices Influence the Breast Milk Microbiota Depending on Pre-Gestational Maternal BMI and Weight Gain over Pregnancy

Breastfeeding is critical for adequate neonatal microbial and immune system development affecting neonate health outcomes in the short and long term. There is a great interest in ascertaining which are the maternal factors contributing to the milk microbiota and the potential relevance for the developing infant. Thus, our study aimed to characterize the effect of mixed and exclusive breastfeeding practices on the milk microbiota and to determine the impact of pre-pregnancy body mass index (BMI) and weight gain over pregnancy on its composition. Breast milk samples from 136 healthy women were collected within the first month post-partum and milk microbiota profiling was analyzed by 16S rRNA gene sequencing. Information on breastfeeding habits and maternal-infant clinical data were recorded. Breastfeeding practices (exclusive vs. mixed), maternal pre-gestational BMI, and weight gain over pregnancy contributed to the milk microbiota variation. Pre-gestational normal-weight women with exclusive breastfeeding habits harbored a significantly higher abundance of Bifidobacterium genus, and also, higher alpha-diversity compared to the rest of the women. Our results confirm the importance of controlling weight during pregnancy and breastfeeding practices in terms of milk microbiota. Further studies to clarify the potential impact of these maternal factors on milk and infant development and health will be necessary.

Can we modulate the breastfed infant gut microbiota through maternal diet?

Initial colonisation of the infant gut is robustly influenced by regular ingestion of human milk, a substance that contains microbes, microbial metabolites, immune proteins, and oligosaccharides. Numerous factors have been identified as potential determinants of the human milk and infant gut microbiota, including maternal diet; however, there is limited data on the influence of maternal diet during lactation on either of these. Here, we review the processes thought to contribute to human milk and infant gut bacterial colonisation and provide a basis for considering the role of maternal dietary patterns during lactation in shaping infant gut microbial composition and function. Although only one observational study has directly investigated the influence of maternal diet during lactation on the infant gut microbiome, data from animal studies suggests that modulation of the maternal gut microbiota, via diet or probiotics, may influence the mammary or milk microbiota. Additionally, evidence from human studies suggests that the maternal diet during pregnancy may affect the gut microbiota of the breastfed infant. Together, there is a plausible hypothesis that maternal diet during lactation may influence the infant gut microbiota. If substantiated in further studies, this may present a potential window of opportunity for modulating the infant gut microbiome in early life.

Best Practices for Human Milk Collection for COVID-19 Research

In addition to providing life-giving nutrients and other substances to the breastfed infant, human milk can also represent a vehicle of pathogen transfer. As such, when an infectious disease outbreak, epidemic, or pandemic occurs-particularly when it is associated with a novel pathogen-the question will naturally arise as to whether the pathogen can be transmitted through breastfeeding. Until high-quality data are generated to answer this question, abandonment of breastfeeding due to uncertainty can result. The COVID-19 pandemic, which was in full swing at the time this document was written, is an excellent example of this scenario. During these times of uncertainty, it is critical for investigators conducting research to assess the possible transmission of pathogens through milk, whether by transfer through the mammary gland or contamination from respiratory droplets, skin, breast pumps, and milk containers, and/or close contact between mother and infant. To promote the most rigorous science, it is critical to outline optimal methods for milk collection, handling, storage, and analysis in these situations, and investigators should openly share their methods in published materials. Otherwise, the risks of inconsistent test results from preanalytical and analytical variation, false positives, and false negatives are unacceptably high and the ability to provide public health guidance poor. In this study, we provide "best practices" for collecting human milk samples for COVID-19 research with the intention that this will also be a useful guide for future pandemics.