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

Abstract

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.

Introduction

Human milk is highly nutritious and possesses a unique composition in terms of a higher amount of protein, lactose, and specific growth factors and microbiome. It is considered an ideal food for infant nutrition owing to the presence of certain nutritional factors such as lactoferrin, immunoglobulins, and leukocytes conferring immunity to the infants.¹ Diverse microorganisms present in the initial streams of human milk modulate the colonization of microbiota in the small intestine of infants and it has been recognized that it significantly affects the development and maturation of the infant's immune system. Thus, breastfeeding is considered critical for the overall growth and development of newborns as it establishes local and systemic immune tolerance to the foreign molecules ingested during breastfeeding.² Although human milk is considered sterile, recently researchers have established the presence of certain commensals and other probiotic bacteria considered the best for infant's gut.³

Staphylococci, Bifidobacteria, Streptococci, and lactic acid bacteria are certain microorganisms found in human milk. Among these, Bifidobacteria is considered to stimulate the growth of other potential healthy bacteria in the newborn gut system, although the origin of all these bacteria remains controversial.^3,4 Human milk ingested by newborns (800 mL/day) contains around 105–107 bacteria, which proves the close proximity of the gut microbiota of the infant to the mother's milk. Furthermore, human milk oligosaccharides (HMOs) have an essential role in the development of healthy bacteria in breastfed infants. Lactobacillus strain in human milk is found to stimulate the production of cytokines and inflammatory mediators (CD4+, CD8+, natural killer cells, and regulatory T cells).⁵ Human milk bacteria serve as biotherapeutic agents as these are considered to possess probiotic potential, antiallergic, antiarrhythmic, and inhibiting the infectivity of HIV and others.

Therefore, this review underlines the significance of diverse human milk microbiota and its role in the protection of certain diseases and ailments in newborn and infants. It also highlights certain factors that can influence the composition of milk thereby affecting the overall growth and development of the newborn.

Human Milk Microbiota

Breastfeeding has strong beneficial effects on infantile immunity,⁶ cognitive development,^7–9 protection against sudden infant death syndrome,^10,11 and infections.^12–14 Moreover, increasing evidence suggests that breastfed infants are better protected against noncommunicable chronic diseases later in their life, including type 1 and 2 diabetes mellitus, obesity, cardiovascular diseases, allergies, asthma, and inflammatory bowel disease, than nonbreastfed infants.^15–19 With the increase in the incidence of noncommunicable chronic diseases recently, research on the potential relationship between the developmental origins of these diseases and early infant microbial colonization has become interesting.

Human milk contains diverse bacterial species and hosts bacteria at concentrations of approximately 10³ colony-forming units (CFUs).^20–22 Using the culture-dependent and/or culture-independent methods, many studies have explored the microbial diversity of human milk and the infant's gut and revealed the co-occurrence of bacteria in human milk and the infant's gut, endorsing the hypothesis of vertical bacterial transmission from milk to the infant gut.^22–24 Recently, the taxonomic classification at the strain level of bacteria revealed that Streptococcus spp. and Veillonella dispar are shared by human milk and correspond in the feces of infants.²⁵ It has also been reported that this co-occurrence is reduced depending on breastfeeding methods such as breast pumps and feeding from a bottle.²⁵ Apart from the method of breastfeeding, epidemiological studies have revealed that gut microbiota composition differs in breastfed and formula-fed infants.^25,26

A study from Northeast China showed that the differences in gut microbiota and metabolite composition of healthy infants were related to various feeding methods, such as exclusively breastfeeding, mixed-feeding, exclusively formula-feeding, and complementary feeding.²⁶ The study reported that exclusively breastfed infants have decreased bacterial species richness or diversity, but have a more stable microbial community, containing a higher abundance of saccharolytic species to provide health-promoting benefits to their hosts such as Bifidobacterium and Lactobacillus.²⁶ Moreover, the gut microbiota of formula-fed infants seems to have increased richness and diversity with higher numbers of Enterococcus, Enterobacter, Citrobacter, Escherichia coli, and Clostridium difficile.^27–30

In a meta-analysis of seven microbiome studies from five different countries (the United States, Canada, Haiti, South Africa, and Bangladesh), 1,825 feces samples from 684 infants were examined.³¹ According to the results of the meta-analysis, intestinal bacterial diversity, microbiota age, and relative abundances of Bacteroidetes/Firmicutes in the first 6 months of life were found to be higher in nonexclusively breastfed infants compared with exclusively breastfed infants. The results of the study suggested that exclusively breastfeeding is associated with a more steady, less diverse, gut microbiota, which may be necessary for the early months of development.³¹

Bacterial Diversity of Human Milk

Human milk is the first and major source of both HMOs and microorganisms for early infant microbial colonization.^32–34 In colostrum (0–5 days), there are higher microbial contents than in transitional (6–14 days) and mature milk (15–90 days).³⁵ Many studies have searched for the difference in microbial contents of human milk regarding lactation stages.^35–42 The results of the studies are summarized in Table 1. Colostrum is characterized by an increased abundance of Weissella, Leuconostoc, Staphylococcus, Streptococcus, and Lactococcus.²⁰ Damaceno et al. found that the total bacterial concentration in colostrum (median: 3.44 log₁₀ CFU/mL) was higher than in transitional (2.2 log₁₀ CFU/mL) and mature milk (2.68 log₁₀ CFU/mL) (p < 0.00001; however, more genera were identified in transitional and mature milk than in colostrum.³⁵

Table 1.

Microbial Diversity in Human Milk

Participants	Delivery mode	Feeding method	Stages of lactation	Analytical method	Bacterial diversity	Region	Ref.
n = 24 healthy mothers	29.17% delivered vaginally, 70.83% cesarean section	NS	Colostrum, transitional, and mature milk	MALDI-TOF MS and 16S DNA sequencing	Staphylococcus epidermidis, Staphylococcus aureus, Staphylococcus hominis, Staphylococcus lugdunensis, Staphylococcus capitis, Streptococcus vestibularis, Leuconostoc mesenteroides, and Lacticaseibacillus rhamnosus ^Comparing the bacterial counts during the lactation period, it was shown that there is a higher bacterial count in colostrum samples than in transitional and mature milk ^No significant differences in human milk microbiota comparing the delivery method	Brazil	³⁵
n = 47 healthy women	57.4% delivered vaginally and 42.6% cesarean section	NS	Colostrum, transitional, and mature milk	MALDI-TOF MS	The most dominant species: Staphylococcus epidermidis. Lactobacillus gasseri, Bifidobacterium breve, and Streptococcus salivarius were identified as potential probiotics	Brazil	³⁶
n = 20 mother–infant pairs	45% delivered vaginally	75% latched for breastfeeding, 25% never-latched	Late lactation period (weeks 21–48)	16S rRNA gene sequencing and shotgun metagenomics	Never-latched group: Staphylococcus, Finegoldia, and Corynebacterium. Latched group: Staphylococcus, Streptococcus, Acinetobacter, Enterobacter, Corynebacterium, Veillonella, and Haemophilus	The United States	⁵²
n = 10 healthy lactating women	60% delivered vaginally and, 40% cesarean section	Breastfeeding for at least 4 weeks after birth	Weeks 1, 3, 6, and 12	Culture-independent	Staphylococcus, Streptococcus, Bifidobacterium, Lactobacillus, Elizabethkingia, Pseudomonas, Variovorax, Flavobacterium, Stenotrophomonas, Brevundimonas, Chryseobacterium, and Enterobacter	Ireland	³⁷
n = 39 healthy lactating women	NS	NS	Day 6 and onward postpartum	Culture-independent	Staphylococcus, Enterobacteriaceae, Pseudomonas, Streptococcus, and Lactobacillus	Canada	⁶⁷
n = 16 healthy women	100% delivered vaginally	NS	Weeks 1 and 4	Culture-independent	Lactobacillus, Staphylococcus, Rothia, and Streptococcus	Finland	³⁸
n = 84 healthy women	72.6% delivered vaginally	70% exclusive breastfeeding	1 Month postpartum	Culture-independent	Streptococcaceae, Staphylococcaceae, Oxalobacteraceae, Moraxellaceae, Rhizobiales, Gemellaceae, Comamonadaceae, Micrococcaceae, Veillonellaceae, Alphaproteobacteria, Corynebacteriaceae, and Sphingomonadaceae	Finland	⁶⁸
n = 99 healthy lactating women	86.2% delivered vaginally	NS	1.3, 2.5, 6.5, 8.2, 12.5, 31.3, and 41.6 months postpartum	16S rRNA gene sequencing and quantitative real-time PCR	Streptococcaceae, Staphylococcaceae, Enterobacteriaceae, Moraxellaceae, Pseudomonadaceae, Propionibacteriaceae, Xanthomonadaceae, Bradyrhizobiaceae, Micrococcaceae, and Carnobacteriaceae	Spain	¹⁴³
n = 31	62% delivered vaginally	NS	At birth and 2 months postpartum	16S rRNA gene sequencing	Streptococcus, Staphylococcus, Gemellaceae, Neisseriaceae, Caulobacteraceae, Micrococcaceae, Pasteurellaceae, Propionibacteriaceae, Comamonadaceae, and Lactobacillaceae	Finland	⁴⁰
n = 80 (20 each country)	50% delivered vaginally	NS	1 Month postpartum	16S rRNA gene sequencing	Streptococcus (China) Firmicutes (Finland) Enterobacteriaceae and Pseudomonadaceae (South Africa) Cutibacterium, Pseudomonas (Spain)	China, Finland, South Africa, and Spain	⁵⁶
n = 25 healthy Uyghur mother	100% delivered vaginally	36% exclusively breastfeeding, 64% partial feeding	7–720 days	Next-generation sequencing datasets of the bacterial 16S rRNA gene	Proteobacteria (46.5%), Enterobacteriaceae (25.5%), Streptococcaceae (19.3%), and Pseudomonadaceae (2.2%)	Kashgar, Xingjiang, China	⁴¹
n = 412 healthy lactating women from 11 different populations	Delivered vaginally: 100% Ethiopian rural area, Ethiopian urban area, The Gambia rural area; 97% The Gambia urban area; 92% Ghana, 78% Kenya, 51% Peru; 90% Spain; 79% Sweden; 63% U.S. California; 79% U.S. Washington¹⁴⁴	Exclusively breastfed: 95% Ethiopian rural area, 87% Ethiopian urban area, 97% The Gambia rural area, 53% The Gambia urban area, 34% Ghana, 36% Kenya, 31% Peru, 62% Spain, 48% Sweden, 50% U.S. California, 57% U.S. Washington¹⁴⁴	NS	Metataxonomic analysis-targeted 16S rRNA hypervariable regions	Firmicutes, Proteobacteria, Actinobacteriota, and Patescibacteria Higher relative abundance of Proteobacteria in the African cohorts, Patescibacteria in the European countries (p < 0.001). Lower relative abundance of Streptococcus and higher relative abundance of Lactobacillus in African cohorts (p < 0.001) (at the genus level)	Sweden, Spain, the United States, Peru, Ethiopia, Ghana, Kenya, and Gambia	¹⁴⁵
n = 22 lactating mothers	100% delivered vaginally	100% Exclusive breastfeeding	At a postnatal age ≤7 days	16S rRNA gene sequencing	Proteobacteria (84%), Actinobacteria (5%), Firmicutes (8%), Bacteroidetes (3%)	North India	¹⁴⁶
n = 117	NS	NS	Colostrum, transitional milk, and mature milk	16S rRNA gene sequencing	At the phylum level: Proteobacteria, Firmicutes At the genus level: Staphylococcus, Streptococcus, Lactobacillus, Acinetobacter, Pseudomonas Human milk microbial diversity was the highest in colostrum and then decreased across lactation time	China	⁴²
n = 117 women	56.6% delivered vaginally and 43.4% cesarean section	NS	At 3 months postpartum	V4-16S ribosomal RNA gene sequencing	At the phylum level: Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, and Fusobacteria At the genus level: Pseudomonas, Streptococcus, Staphylococcus, Acinetobacter, Veillonella, Gemella, Corynebacterium, Rothia, Aeromonas, and Brevundimonas	Canada	¹⁴⁷
n = 78 breastfeeding women (aged 18–55 years)	81.8% delivered vaginally and 18.2% cesarean section	NS	Over 1-week period between 6 and 8 weeks postpartum	V3–V4 hypervariable region of the 16s rRNA gene	Ruminococcaceae, Bifidobacterium, and Lachnospiraceae No significant differences in human milk microbiota compared with the delivery method and human milk microbiota varied among the ethnic groups (Asian, Maori and Pacific Island, and Europeans), but not BMI classifications	New Zealand	¹⁴⁸

BMI, body mass index; MALDI-TOF MS, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry; NS, not specified; PCR, polymerase chain reaction; rRNA, ribosomal RNA.

A recent study revealed a significant decrease in microbial diversity throughout the first 6 months of lactation, especially between weeks 8 and 24.⁴³ Similarly, previous studies have shown that as lactation progresses, bacterial diversity decreases,^20,37,42 and it may be related to the change in the nutritional composition and bioactive compounds of human milk during the lactation stages. Higher availability of proteins, immunoglobulins, cytokines, and HMOs in the colostrum may contribute to higher microbial diversity.⁴⁴

Origin of Human Milk Microbiota

The microbial content of the colostrum, which is the first contact of the newborn, is the microorganism that first colonizes the baby's intestines. Many studies have demonstrated that human milk microbiota is transmitted from mother to infant at the species and/or strain level.^{23,24,37,45,46} Although breast milk has emerged as a source of infant gut bacteria, the origin of human milk microbiota is still largely unknown. It was previously considered that bacteria found in human milk originated from the infant's oral cavity and the mother's breast skin. However, the finding of anaerobic bacteria associated with the gut microbiota in human milk by culture-dependent and/or culture-independent methods has sparked new debates about the origin of breast milk microbiota.^20,47–50

Martı´n et al.⁵¹ hypothesized that maternal gut-originated bacteria could transmit to the infant through breastfeeding due to changes in the lactating mammary gland. They suggested that all changes in the mammary areola and mammary canal system, including enlargement of the nipple and areola, increased lymph and blood flow to the mammary gland, and contraction of myoepithelial cells under the influence of oxytocin, may prepare a suitable environment for the bacterial transmission.⁵¹ In a study investigating the factors contributing to the breast milk microbiome, a distinct strain of Bifidobacterium breve was determined in the maternal gut, breast milk, and infant's gut.⁵² The fact that the baby was delivered by cesarean section limits the risk of transmission of this anaerobic bacterial strain during delivery and strengthens the presence of microbial translocation via the enteromammary pathway.⁵²

Another finding supporting the enteromammary pathway is that colostrum samples obtained before first infant feeding already harbors a microbial community.³⁶ As mentioned above, one of the two main pathways suggested for the origin of human milk microbiota is the enteromammary pathway, and the other is retrograde inoculation by the infant's oral microbiota.⁵³

The exact origin of the microorganisms (skin, oro-nasopharynx, maternal gut, vaginal delivery) in human milk is difficult to determine due to the complex and interactive relationship between mother and infant. Many external factors affect the composition of human milk microbiota (breast pump, nipple shield, water, other breastfed sibling, clothes, family, medical staff, pets, etc.) apart from the enteromammary pathway and retrograde inoculation. Figure 1 shows the factors affecting the human milk microbiota.

FIG. 1.

Origin of the human milk microbiota. Maternal and exogenous microbiota plays important roles in the origin of human milk microbiota, which eventually affects infant gut and health.

Maternal Factors That Influence Microbial Composition of Human Milk

Maternal factors that influence the microbial composition of human milk include diet and habits, gestational age, mode of delivery, parity, lactation stages, mastitis, obesity, cancer, celiac disease, gestational diabetes, HIV, and coronavirus disease 2019 (COVID-19). Besides, the infant's gender and the nutrition method also compose other factors that influence the microbial composition of human milk (Fig. 2).

FIG. 2.

Maternal factors that influence the microbial composition of human milk. There are many maternal factors that affect the microbial composition of human milk such as obesity, diet, mode of delivery, gestational age, and medications.

Lifestyle habits

Human milk is a highly complex compound for infant growth, consisting of fat, carbohydrates, proteins, minerals, vitamins, and other nutrients. With the balance of nutrients, human milk has become sufficient as the sole source of nutrition for a while in an infant's life. The interaction of macronutrients, micronutrients, and bioactive factors in human milk and the biochemistry of human milk change during breastfeeding stages and according to the needs of the infant.⁵⁴ Nutrition received through the maternal diet affects the content, taxonomic components, and microbiota of human milk. Some studies report that the content of human milk changes according to the diet and local food received by the mother.^55–59 Albesharat et al. reported that since fermented food is highly consumed in Syria, the breast milk of Syrian women contains higher levels of Lactobacillus plantarum.⁵⁵

Williams et al. reported that overweight and obese women produce milk with relatively higher abundance of Granulicatella. The Granulicatella level increases with the increase in energy intake. Moreover, saturated fatty acids and monounsaturated fatty acids in the mother's diet were inversely associated with the relative abundance of the Corynebacterium level.⁵⁸ Similarly, Kumar et al. reported a negative relationship between saturated fatty acids and Corynebacterium and Streptococcus.⁵⁶ Padilha et al. associated vitamin C consumption during pregnancy with a high Staphylococcus level in breast milk content during lactation. Increased glucose intake in lactation decreases the Pseudomonas level.⁵⁷ Compared with the lactation period, the mother's diet during pregnancy affects human milk microbiota further.

Vitamin C consumption during pregnancy is associated with the components of human milk microbiota. Furthermore, the polyunsaturated fatty acid (PUFA)/linoleic fatty acid level in the newborn's gut microbiota is closely associated with the increase in the amount of Bifidobacterium in human milk.⁵⁷ It causes changes in the human milk microbiota of Italian and Burundian mothers who have different lifestyles and dietary habits. However, besides lifestyle and dietary habits, other factors can affect the microbiota between these two populations. Especially in Burundi, factors such as younger mothers, lower passive smoking exposure, and higher prenatal antibiotic use affect human milk microbiota.⁶⁰ The fatty acid (FA) composition of milk varies according to dietary patterns. In the study evaluating the FA composition and the results of the diet in the milk of lactating Tibetan women, n-3 PUFA, linoleic acid, and α-linolenic acid (ALA) were found to be deficient, including docosahexaenoic acid (DHA).

Besides, the Tibetan maternal diet is primarily rich in Zanba (butter tea). However, the intake of fatty fish, vegetables, and fruits in the diet is insufficient. Therefore, this situation led to a high carbohydrate intake in mothers. Carbohydrate intake affects the main FAs in milk. Because of this study, a negative correlation was found between carbohydrates and eicosapentaenoic acid and DHA concentrations. In this regard, it is recommended that lactating mothers living in the region consume diets rich in DHA.⁶¹ There are water-soluble B vitamins (B1, B2, B3, B6, B9, B12), vitamin C, and fat-soluble vitamins A and E in human milk. B vitamins are coenzymes in metabolic processes and are crucial for neurotransmitter synthesis. In infants who are not treated for vitamin B1 deficiency, beriberi develops. Vitamins C and E, which are antioxidants, protect tissues from oxidative stress and damage in the early postnatal period.

Vitamin A is critical for vision, cell growth and development, and immune system function. Although human milk is a good source of these vitamins, it is not an adequate source of vitamins D and K. Because vitamin D is the vitamin responsible for bone health and vitamin K is responsible for blood clotting, it is important for the baby. In this regard, vitamin D and K supplements are provided to the newborn in the postpartum period.⁵⁴ Maternal vitamin supplementation is important in the case of need. However, these supplements can cause changes in human milk content. Maternal vitamin A supplementation significantly increases retinol, α, and β-carotene concentrations in human milk. Maternal vitamin D supplementation, on the contrary, increases 25-hydroxy-D levels in human milk.

A higher level of ascorbic acid was observed in the human milk of women taking vitamin C supplements. The levels of α-tocopherol increased in the human milk of women who took vitamin E supplements. Breastfeeding mothers should consume all essential nutritional sources both for their health and for protecting human milk concentrations.⁶² During the breastfeeding period, habits are important and diet. Smoking is reported to affect human milk negatively.⁶³ The milk of mothers who smoked during the lactation period contains lower fat and energy. This condition is considered to be caused by smoking-related toxic effects accumulated in fatty tissues, particularly in mammary glands.⁶³

In a study evaluating the effect of exercise on human milk, it was reported that interleukin (IL)-8 and tumor necrosis factor-α (TNF-α) concentrations in mothers who exercised were 36% and 27% lower, respectively, compared with the control group. There was 22% lower IL-6 in the colostrum of mothers who continued the exercise program, 30% more fractalkine, and 20% higher IL-10 in mature milk.⁶⁴ Another factor affecting breastfeeding and the mother–infant relationship is stress. The stress factors of the mother and the stressful lifestyle can affect the content of human milk. The mechanisms underlying the transmission of maternal stress to the child remain unclear. In a Dutch study, maternal stress in the first month postpartum was generally associated with overall lower levels of FA in human milk. This may indicate a pathway for transmitting maternal stress signals to an infant.⁶⁵

Gestational age

Gestational age is a factor that affects the content of human milk. The content of human milk microbiota changes according to the time of labor.⁵⁹ Compared with preterm deliveries, Bifidobacterium levels were reported to be higher in mothers who have term delivery.⁶⁶ However, the time of labor was reported not to affect bacterial components in human milk in another study.⁶⁷

Mode of delivery

The content of human milk could differ by the mode of delivery. Khodayar-Pardo et al. reported that while women who had a cesarean section had higher bacterial concentrations in colostrum and transitional milk, women who delivered vaginally had higher levels of Bifidobacterium.⁶⁶ Hermansson et al. reported that human milk microbiota had relatively less diversity in women who had a cesarean section compared with women who delivered vaginally.⁶⁸ Burianova et al. reported that women who had vaginal delivery had higher carbohydrate content in their milk.⁶³ In addition to the mode of delivery, antibiotics used during labor could also affect human milk microbiota. The mode of delivery is reported to have more effects on the microbiota composition according to intrapartum antibiotic administration.⁶⁸ On the contrary, in some studies, the mode of delivery was reported to have no effects on human milk microbiota.⁶⁷

Infant's sex

The biological sex of the infant is a factor that can affect the human milk microbiota. Moossavi et al. reported that women who had a male infant had more limited human milk microbiota diversity.⁶⁹ Williams et al. reported that the milk of women who had a male baby was richer in terms of Streptococcus.⁵⁸ On the contrary, some studies in the literature indicated that the infant's sex did not affect human milk microbiota.⁶⁷ It has been reported that the composition of animal milk differs according to the sex of the offspring.^70,71 However, studies showing the relationship between human milk compositions and infant sex are limited.^72–76 The findings of these limited study are contradictory. It has been reported that there is no relationship between breast milk composition and infant sex in the Filipino population.⁷²

On the contrary, it has been reported that the energy in human milk is higher in male infants in the American population, and in female infants in the Korean and Kenyan populations.^73–75 Researchers emphasize that the content of human milk is not only related to sex and can be affected by many other factors. In particular, socioeconomic status is stated to be a related factor that has a significant effect on human milk content.⁷⁶ There is higher level evidence that male infants with a higher growth rate than female infants consume greater amounts of breast milk. Increased milk consumption in male infants is associated with increased nutritional needs.⁷⁷ In a study with Chinese, Malay, and Indian populations, mothers of the postpartum first 3 months of male infants reported higher levels of energy and lipids in human milk.

In human milk of mothers with male infants, lipids were found to be 39% higher and energy 24% higher.⁷⁸ It has been reported that higher concentrations of free amino acids, glutamine, glutamate, glycine, cysteine, and tyrosine associated with male infant sex are observed in mature human milk monitored monthly in the first trimester.⁷⁹ In another study with a 7-month postnatal follow-up, it was reported that the composition of human milk did not differ according to the sex of the newborn.^80,81 All these results suggest that human milk composition may be sex-specific and sex-related differences become less clear 2–4 months after birth.⁷⁷

Parity

A few studies in the literature report that parity affects human milk microbiota. Moossavi et al. showed that human milk microbiota had less diversity in primiparous women in comparison with multiparous women.⁶⁹ Primiparous women have higher protein and lower carbohydrate levels in their breast milk, yet some other studies in the literature report that parity does not have effects on human milk microbiota.^63,69

Lactation stages

Human milk composition varies according to the lactation stage. The colostrum content is rich in proteins, minerals, antibodies, antimicrobial peptides, complement factors, cytokines, lysozyme, and HMOs. During the transition from colostrum to mature milk, while protein and mineral concentrations decrease, lipid and carbohydrate concentrations increase. Studies show that colostrum has more varied microbiota than mature milk.^59,82 However, some other studies claim that mature milk has more varied microbiota than colostrum.^{36,39,60,66,82} The literature also includes studies indicating that colostrum and mature milk are similar in terms of microbiota.^67,83,84

Using a breast pump

In addition to being nutritious, human milk is a protective factor for the infant thanks to the microbiota diversity it has due to being nonsterile. In a physiological translocation mechanism, the maternal gut microbiota is considered to be transported to the mammary gland during breastfeeding. The presence of bacterial communities accumulated in the colostrum before the first lactation supports this condition.⁸⁵ This process could be explained by physiological and hormonal changes and increased permeability in the gut epithelium during late pregnancy. Mononuclear cells, dendritic cells, and CD18 cells are involved during the transition of these microbes from the gut to the breasts.⁸⁶ By loosening the connections between gut epithelial cells and passing bacteria through the intestinal lumen, dendritic cells penetrate the gut epithelium, making the transportation of bacteria possible by macrophages to the mesenteric lymph nodes and eventually to the mammary gland.^87,88

Human milk can be given to the baby in ways other than breastfeeding. Milking techniques affect human milk microbiota, but aseptic conditions are one of the most important factors causing microbiota diversity. Human milk samples taken in aseptic conditions indicated less microbiota diversity.^22,47,84 Besides, the microbiota of women who fed their baby only with breast milk was reported to be richer than that of women who used mixed feeding.⁸⁹ Moossavi et al. reported that breast milk milked with a pump was poorer in terms of microbiota than breast milk milked by hand.⁶⁹

Obesity

Maternal body mass index before pregnancy is important in the development of human milk and an infant's gut microbiota.⁹⁰ The breast milk of obese women involves high fat and energy levels. However, the woman's weight has no effects on the human milk calorie. The protein level is high in mothers who are overweight and obese, yet mature milk demonstrates differences according to the mother's fatty mass. While total saturated and n-3 PUFAs decrease, monounsaturated and n-6 PUFAs increase in the colostrum of women who are overweight or obese.^63,91

Mastitis

Mastitis is usually related to an infection from Staphylococcus aureus. The use of probiotics as an alternative or supplementary to antibiotic treatment is of importance in the management of mastitis.^92–94 The use of probiotics is reported to be beneficial for preventing mastitis-related dysbiosis.⁹⁵ However, some studies indicate that probiotic treatment causes a significant decrease in the number of bacteria in human milk.⁹⁶ A study investigated women diagnosed with mastitis who were administered Lactobacillus fermentum, CECT 5716 or CECT 5713 Lactobacillus salivarius, and antibiotics daily for 3 weeks. While the average amount of bacteria was similar in the three groups on day 0, the amount of bacteria was found to be lower in the probiotic groups in comparison with the control group on day 21.

The probiotic treatment was found to cause a significant decrease in the abundance of milk bacteria. After the probiotic supplementation, Lactobacillus salivarius ECT 5713 and Lactobacillus fermentum CECT 5716 could be identified in women's milk samples. Women in the antibiotic group were found to have significant differences in decreasing the number of bacteria and improving pain scores.⁹⁶

Cancer and cancer treatments

As cancer cells may include estrogen receptors, they could multiply rapidly. Therefore, anticancer medicine could demonstrate a more toxic effect on rapidly multiplying cells. Cancer cells are considered not to maintain their presence in mammal tissues during the breastfeeding period due to the effects of high calcium concentrations and fluidity of the milk. Fluidity plays a natural barrier role in the human body. Diseases such as cancer develop when the fluidity decreases in the body. Hence, breastfeeding could demonstrate a protective effect mechanism against cancer.⁹⁷

The mother's receiving chemotherapy during lactation also affects human milk microbiota. Urbaniak et al. analyzed the human milk content of a breastfeeding woman who received chemotherapy due to Hodgkin's lymphoma at 2-week intervals for 4 months. Throughout the treatment, decreases were found in Bifidobacterium, Eubacterium, Staphylococcus, Cloacibacterium, DHA, and inositol metabolites. This change in the microbiota reduces the useful effects of human milk.⁶⁷ “Human alpha-lactalbumin made lethal to tumor cells (HAMLET)” is an important component that has a bactericide effect on human milk content. This component is a complex structure that is composed of human α-lactalbumin and oleic acid. HAMLET has a killing effect on gram-positive bacteria with a mechanism similar to apoptosis in eukaryotic cells.⁹⁸ Glycolytic enzymes are required for the full demonstration of HAMLET activity. Hence, HAMLETs mediating a change in cancer cell metabolism as part of death induction could be explained by glycolysis inhibition.⁹⁹

Brisuda et al.¹⁰⁰ presented the first human placebo-controlled double-blind experimental study that analyzed the effects of HAMLET on cancer cells. The study group (n = 40) was composed of individuals who had nonmuscle invasive bladder cancer. The study formed alpha-helical peptide oleic acid complexes (alpha1-oleate) from the A39 residue obtained from alpha-lactalbumin. The patients received six infusions of alpha 1H or placebo treatment for 22 days. The study results showed that intravesical instillations of alpha1-oleate enabled the shrinking of tumor cells significantly and made their size smaller. No significant side effects were detected after the treatment.¹⁰⁰ Hence, studies support that HAMLET had a killing effect on the cancer cells.^98,100

Gestational diabetes

Human milk microbiota changes with the effects of the metabolic changes happening during the pregnancy period. Gestational diabetes mellitus (GDM) and maternal obesity cause dysbiosis of the gut microbiota. In this regard, it could also affect human milk microbiota via the breast. The gut microbiota of obese women has less diversity.^101,102 In a similar vein, the gut microbiota of women with GDM is also reported to have low diversity.¹⁰³ In this regard, these changes experienced in microbiota affect human milk content and cause an obesogenic environment in the infant's gut. This condition is a factor that increases the baby's risk of obesity.^102,103 A study reported higher amounts of Gemella in the breast milk of obese women with GDM or impaired glucose tolerance. On the contrary, apart from diabetes and obesity, human milk microbiota is reported to be affected by factors such as the use of antibiotics and an infant's sex.¹⁰²

Villamil et al. reported that in the late lactation period, Immunoglobulin A (IgA) and Immunoglobulin M levels were lower in human milk of celiac disease patients. While IL-6, TNF-α, and monocyte chemoattractant protein-1 were the highest in these women's milk, the soluble Toll-like receptor-2 prevalence was found to be lower.¹⁰⁴

Celiac disease

Celiac disease is a chronic autoimmune small bowel disease that emerges with intolerance against gluten-containing food. A study conducted showed that celiac disease and a gluten-free diet did not have effects on human milk microbiota. However, compared with healthy women, human milk microbiota was shown to be more diverse in women with a continuing risk of celiac disease.¹⁰⁵ Olivares et al. reported that the human milk of patients with celiac disease contained significantly lower IL 12p70, transforming growth factor (TGF)-β1, Bifidobacterium, Bacteroides fragilis group, IgA, and interferon (IFN) levels. These changes in human milk content could decrease its protective effects on babies against celiac disease.¹⁰⁶

Olshan et al. analyzed the human milk microbiome in the study groups composed of gluten-free diet (n = 20) celiac patients and healthy controls (n = 16). Three increased bacterial strains were found as Acinetobacter ursingii SM 16.037 = CIP 107286, Rothia mucilaginosa ATC 25296, and Acinetobacter sp. 479375 in women with celiac disease who received a gluten-free diet. Besides, there was an increase in Bacillus cereus abundance. The four increased bacterial strains in the human milk of healthy women were found as Bacteroides, Faecalibacterium prausnitzii, Clostridiales, and Gemella.¹⁰⁷ Human milk microbiota (Bifidobacterium) of healthy women and women with celiac disease was found to demonstrate differences in terms of immunity agents (IgA) and TGF-β1.¹⁰⁸ These differences in human milk microbiota affect infants' immune systems by changing their gut microbiota.¹⁰⁵

HIV

The literature excludes clear evidence on whether the HIV infection is transmitted via breast milk. Human milk is considered the source of pediatric HIV-1 infection. However, there is evidence showing that the babies breastfed by HIV-positive women were not infected. In this regard, human milk is seen as both a transmission factor and a protection factor for HIV-1.⁹³ CD4+ cells in human milk have a protective effect against HIV.¹⁰⁹ A study measured the HIV-specific secretory IgA (SIgA) level of human milk in mothers whose baby was infected with HIV (n = 26) and who were not (n = 64). HIV-specific SIgA, HIV RNA, CD4 counts in human milk, and plasma RNA amounts were found to be similar in both groups. HIV-specific SIgA in human milk did not show a protective effect against HIV transmission.¹¹⁰ In this regard, particularly in developing countries, HIV-positive women are generally encouraged to breastfeed their babies.

Depending on local and individual conditions, the main justification for breastfeeding is that HIV infections transmitted via human milk enable protection against morbidity and mortality associated with optimal nutrition for infant, diarrhea, and lower respiratory tract infections.⁹³ A study that investigated human milk microbiota compositions of women who have and who do not have HIV RNA in their breast milk found that human milk that had HIV RNA had higher levels of bacterial diversity and Lactobacillus spp. ratio. Bifidobacterium, Streptococci, and Enterococci are reported to be the primary bacterial groups in the infant's feces.⁸⁹ On the contrary, another study reported that human milk microbiota of HIV (+) and HIV (−) women indicated no significant differences in terms of their compositions. Besides, bacterial diversity was also found to be similar to each.¹¹¹

COVID-19

There were uncertainties regarding medical protocols at the start of the pandemic. In the early times of the pandemic, breastfeeding and skin-to-skin contact of mothers with COVID-19 (+) were delayed.³ Demers-Mathieu et al. reported a positive relationship between antigen samples and secretory antibodies in human milk samples taken from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-positive women.¹¹² Breast milk of women who were infected with SARS-CoV-2 enables protection against COVID-19 and passive immunity for their babies.^45,113,114 However, human milk samples taken from women who were SARS-CoV-2-positive or who had previously been infected with SARS-CoV-2 included no RNA.¹¹⁵ Although the human milk microbiota dysbiosis in SARS-CoV-2-positive women is not yet clear, there is evidence in the literature that COVID-19 may alter the human milk microbiota.¹⁰¹ A change in proteomics and metabolomics has been reported in human milk samples from COVID-19-positive mothers. It is stated that this change develops in three ways as complement activation, platelet degranulation, and macrophage function.¹¹⁶

Although some published guidelines recommend expressing breast milk as an alternative to direct breastfeeding for mothers with positive/suspected SARS-CoV-2 infection, there is substantial evidence to suggest that breastfeeding is an important component of promoting a healthy neonatal microbiome. It has been reported that exposure to the skin of the areola in addition to breast milk is necessary for developing the microbiome. Other infant feeding methods, alternative to breastfeeding, caused depleted Bifidobacteria and an increase in negative microbiota parameters, including the enrichment of potential pathogens. Therefore, direct breastfeeding is recommended.^117,118

Role of Human Milk Microbiota in the Prevention of Disease and Infant Health

Shaping the infant microbiota

The microbiota of the newborns develops and has diversity over time because of some changes. The gut microbiota of the newborn is limited to a few types after birth, but microbiota diversity increases as the baby grows up. In babyhood, there are 1,012 bacteria and around 150–200 bacterial types per gram on average. Maternal microbiota is the main origin of the infant's microbiota. The transmission way of microbes is important in terms of the development of microbiota. Vertically and horizontally acquired microbes have a role in the shaping of the gut microbiota in the early period. Anaerobic clostridia and bacteroides are vertically acquired (birth, enteromammary, etc.) microbes.¹¹⁹ In the first days of life, around 16.3% of the infant's gut microbiota originated vaginally. While the gut of babies born vaginally is rich in Lactobacillus and Prevotella, the gut of babies born via the cesarean section is rich in Staphylococcus, Corynebacterium, and Propionibacterium.^120,121

In the horizontal transmission, microbes are transmitted to the infant from siblings, individuals out of the family, surfaces at home and hospital, animals, complementary food, and the environment. Horizontally acquired microbes are generally composed of facultative anaerobic basils.¹²² Human milk microbiota is important for developing infant gut microbiota (Table 2; Fig. 3). A study in the literature reported that the maternal gut microbiota was rich in Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes, and human milk is considered to be based on maternal gut microbiota.¹²³ Gut microbiota has some differences between infants fed with human milk and infant formula. A study in the literature reported that the gut microbiota of infants who were fed only with breast milk was richer in Bifidobacterium, Staphylococcus, and Streptococcus. The gut microbiota of infants fed with infant formula was reported to be richer in Bacteroides, Clostridium, Enterobacteriaceae, Enterococcus, and Lachnospiraceae.⁵⁹

FIG. 3.

Role of human milk microbiota in the prevention of disease and infant health. Human milk microbiota has been shown to prevent some common diseases during the first year of life and later life such as obesity, asthma, celiac disease, immune system disorders, and gastrointestinal system disorders.

Table 2.

Role of Human Milk Microbiota in the Prevention of Disease and Infant Health

Disorders	Content of human milk and microbiota	Effect on prevention of disease and infant health	Ref.
Obesity	Lactobacillus Bifidobacterium Lactobacillus plantarum 73a or Bifidobacterium animalis subsp. lactis INL1	Antiobesity effect by reducing body weight and fat mass	^124,149
Immune system disorders	Lactoferrin Lactoperoxidase Osteopontin Caseins Lysozyme Superoxide dismutase Acetylhydrolase Alkaline phosphatase Growth factors Hormones Glycosaminoglycans Glycoproteins Glycolipids Oligosaccharides	Protective, anti-inflammatory, and antioxidative effects against infections and cancer	^127,128
Asthma	SCFA	Immunomodulatory and protective effects against the development of allergic diseases	^134,135
Gastrointestinal system disorders	Serum albumin IGF-I Casein Whey SIgA Lactoferrin Lysozyme	Growth and development An antimicrobial effect	¹³⁹
Celiac disease	Interleukin 12p70, TGF-β1 Bifidobacterium Bacteroides fragilis group IgA and interferon	A protective effect against celiac disease	^105,107

IgA, immunoglobulin A; IGF-I, insulin-like growth factor-I; SCFA, short-chain fatty acid-bacterial metabolites; SIgA, secretory IgA; TGF, transforming growth factor.

Another study reported that the Streptococcus parasanguinis ratio was higher in the breast milk of women who fed their babies only with breast milk compared with women who used mixed feeding.⁸⁹

Obesity

Human milk microbiota is reported to be protective against obesity (Table 2; Fig. 3). Various Lactobacillus and Bifidobacterium probiotic strains play a role in this effect mechanism. These strains enable an antiobesity effect by reducing body weight and fatty mass.¹²⁴ Human milk has a direct central effect on the gut microbiota of a 12-month baby.⁹⁰ A causal relationship is considered to exist between the gut microbiota and obesity. In this regard, the mother's use of probiotics enables such benefits as increasing gut barrier integrity, producing beneficial metabolites, and host immune system modulation.¹²⁵

Another study reported that the use of these strains, L. plantarum 73a alone or Bifidobacterium animalis subsp. lactis INL1 under SHIME^® system conditions, in obese infants, increased alpha diversity and healthiness. The administration of both strains leads to a reduction in Proteobacteria, which is associated with an inflammatory condition. In this regard, the use of L. plantarum 73a alone or along with Bifidobacterium animalis subsp. lactis INL1 seems to be a potential probiotic candidate for preventing obesity.¹²⁶

Immune system disease

Human milk has important effects on the infant's immune system and enables passive immunity of the infant. Some components play a role in enabling passive immunity in human milk. These components include lactoferrin, caseins, lysozyme, superoxide dismutase, platelet-activating factor, lactoperoxidase, osteopontin, acetylhydrolase, alkaline phosphatase, growth factors, hormones, some immune cells, glycosaminoglycans, glycoproteins, glycolipids, oligosaccharides, and microbiomes. These components have anti-inflammatory and antioxidative effects against infections and cancer in infants.^127,128 HAMLET, which is obtained from human milk and is a natural complex, is a component that eradicates Streptococcus pneumonia (pneumococcus) and is immune against the development of resistance. It was reported that HAMLET provided an effect that significantly reduced antibiotic concentrations required to eradicate pneumococci in clinically antibiotic-resistant strains.¹²⁹

The lack of Bifidobacterium and oligosaccharide in human milk is associated with systemic inflammation and immune disorders in the first years of life. Bifidobacterium infantis EVC001 suppresses gut T helper (Th)2 and Th17 cytokines and induces IFN-β. It also includes immune-regulatory galectin-1. Galectin-1 provides a connection between beneficial microbes and immune regulation.¹³⁰ Quin et al. analyzed the effect of sulfonated and diet-derived HMOs on infant gut microbiota and immunity. A positive relationship was found between sulfonated and diet-derived HMOs, yet no significant changes were observed in the infant's immune markers.¹³¹

Asthma and allergic diseases

By regulating the baby's immune system, the maternal gut microbiome could be associated with allergic diseases, eczema, and asthma (Fig. 3). Dendritic cells in the gut microbiome decrease allergic airway diseases by stimulating bone marrow hemopoiesis. Prevotella copri carrier is realized with succinate production in the mother during pregnancy. In this way, fetal dendritic cell networks that protect against allergic disease/asthma are established.¹³² In their meta-analysis, Wei et al. reported that the mother's probiotic use did not have effects on preventing eczema or asthma.¹³³ Infants' microbiome has a low genetic potential in allergic diseases for protecting butyrate. This condition highlights the importance of the production of short-chain fatty acid-bacterial metabolites (SCFA) in protecting infants from allergic diseases.¹³⁴ Zuurveld et al. reported that SCFA in human milk has immunomodulatory and protective effects against the development of allergic diseases.¹³⁵

Gastrointestinal system diseases

In addition to food digestion and nutrient absorption, the gastrointestinal system has a defense function in the intestinal tract. Commensal bacteria are abundant in guts (1 × 10¹⁴ CFU) and develop a defense system against agents that cause many diseases. The acidic environment in the stomach and mucosa of the small intestine provide a physical barrier. It is also responsible for sending signals to the lower tissues.¹³⁶ Maternal nutrient intake and the enteromammary pathway are of great importance for developing gut microbiota. Increased, riboflavin, pantothenic acid, vitamin B6, and vitamin B12 intake are associated with an increase in Prevotella and a decrease in Bacteroides.⁸⁸ Since the gastrointestinal and immune systems have not been fully mature in preterm infants and infants with low microbiota diversity, there is a decrease in the protective effect of microbiota and an increase in the risks of necrotizing enterocolitis.^137,138

Besides, the infants' gut microbiota has a protective effect against gut infections and diarrhea.¹³⁵ Casein, whey, SIgA, lactoferrin, and lysozyme in human milk have an antimicrobial effect in the infant's gut. Serum albumin and insulin-like growth factor-I enhance the growth and development of the infant.¹³⁹ With the maintenance of breastfeeding, it is shaped from the skin and gut-derived organisms such as Staphylococcus and Streptococcus to the infant's oral and skin organisms such as Veillonella, Leptotrichia, and Prevotella.²⁰

Celiac disease

Breastfeeding and human milk intake have a protective effect against the early development of celiac disease.¹⁴⁰ A meta-analysis reported that the risk of celiac disease decreases significantly when breastfed babies are given gluten.¹⁴¹ The study by Cilleruelo et al. highlighted that breastfeeding has a protective effect during gluten intake.¹⁴² A protective effect against celiac disease can be provided with IL 12p70, TGF-β1, Bifidobacterium, B. fragilis group, IgA, and IFN in breast milk^.105,107

Conclusion

Human milk contains a plethora of bacteria not only beneficial for the overall growth of newborns but also plays a critical role in the development of the gut system and maturation of the immune system of the newborn and infants. Among several controversies related to the origin of human milk microbiota, it has been successfully established that the mammary gland possesses its own unique microbiota during the late gestation period and early lactation.

However, several factors could influence the human milk and milk microbiota composition such as age, diseased conditions, food habits, and others. Although various lactic acid bacterial strains have been explored for their significant role in immune enhancement and modulation of gut bacteria in infants and newborns, efforts must establish the linkage and correlation of the mother's intestinal bacteria with mammary gland secretion and after that the colonization of bacteria in the newborn gut system. Research toward this field might open new avenues for researchers working in the field of biotherapeutics and probiotics.

Footnotes

Acknowledgment

Figures 1, 2, and 3 were created using .

Authors' Contributions

Drafted the work or revised it critically for important intellectual content and final approval of the version to be published: E.M., A.C., B.Y., and H.S. Designed and drafted the work and revised it critically for important intellectual content and final approval of the version to be published: S.G.S., B.A.V., E.G., F.O., and N.B. All the authors have read and agreed to the published version of the article.

Disclosure Statement

The authors declare no conflicts of interest.

Funding Information

No funding was received for this article.

References

Soyyılmaz

, Mikš

, Röhrig

, et al. The mean of milk: A review of human milk oligosaccharide concentrations throughout lactation. Nutrients, 2021; 13(8):2737.

Petrullo

, Baniel

, Jorgensen

, et al. The early life microbiota mediates maternal effects on offspring growth in a nonhuman primate. iScience, 2022; 25(3):103948.

Notarbartolo

, Giuffrè

, Montante

, et al. Composition of human breast milk microbiota and its role in children's health. Pediatr Gastroenterol Hepatol Nutr May, 2022; 25(3):194–210.

Saturio

, Nogacka

, Alvarado-Jasso

, et al. Role of bifidobacteria on infant health. Microorganisms, 2021; 9(12):2415.

Davis

, Castagna

, Sela

, et al. Gut microbiome and breast-feeding: Implications for early immune development. J Allergy Clin Immunol, 2022; 150(3):523–534.

Silfverdal

, Ekholm

, Bodin

. Breastfeeding enhances the antibody response to Hib and Pneumococcal serotype 6B and 14 after vaccination with conjugate vaccines. Vaccine, 2007; 25(8):1497–1502.

Koh

. Maternal breastfeeding and children's cognitive development. Soc Sci Med, 2017; 187:101–108.

Huang

, Peters

, Vaughn

, Witko

. Breastfeeding and trajectories of children's cognitive development. Dev Sci, 2014; 17(3):452–461.

Wallenborn

, Levine

, Carreira dos Santos

, et al. Breastfeeding, physical growth, and cognitive development. Pediatrics, 2021; 147(5):e2020008029.

10.

Thompson

JMD

, Tanabe

, Moon

, et al. Duration of breastfeeding and risk of SIDS: An individual participant data meta-analysis. Pediatrics, 2017; 140(5):e20171324.

11.

Landa-Rivera

, Pérez-Pérez

, González-Núñez

MDP

, et al. Population-based survey showing that breastfed babies have a lower frequency of risk factors for sudden infant death syndrome than nonbreastfed babies. Breastfeed Med, 2022; 17(2):182–188.

12.

Bowatte

, Tham

, Allen

, et al. Breastfeeding and childhood acute otitis media: A systematic review and meta-analysis. Acta Paediatr, 2015; 104(467):85–95.

13.

Quigley

, Kelly

, Sacker

. Breastfeeding and hospitalization for diarrheal and respiratory infection in the United Kingdom Millennium Cohort Study. Pediatrics, 2007; 119(4):e837–e842.

14.

Kramer

, Chalmers

, Hodnett

, et al. Promotion of Breastfeeding Intervention Trial (PROBIT): A randomized trial in the Republic of Belarus. JAMA, 2001; 285(4):413–420.

15.

Lodge

, Tan

, Lau

, et al. Breastfeeding and asthma and allergies: A systematic review and meta-analysis. Acta Paediatr, 2015; 104(467):38–53.

16.

Horta

, Loret de Mola

, Victora

. Long-term consequences of breastfeeding on cholesterol, obesity, systolic blood pressure and type 2 diabetes: A systematic review and meta-analysis. Acta Paediatr, 2015; 104(467):30–37.

17.

Xue

, Dehaas

, Chaudhary

, et al. Breastfeeding and risk of childhood asthma: A systematic review and meta-analysis. ERJ Open Res, 2021; 7(4):00504-2021.

18.

Kelishadi

, Farajian

. The protective effects of breastfeeding on chronic non-communicable diseases in adulthood: A review of evidence. Adv Biomed Res 2014, 2014; 3(1):3.

19.

, Lochhead

, Ko

, et al. Systematic review with meta-analysis: Breastfeeding and the risk of Crohn's disease and ulcerative colitis. Aliment Pharmacol Ther, 2017; 46(9):780–789.

20.

Cabrera-Rubio

, Collado

, Laitinen

, et al. The human milk microbiome changes over lactation and is shaped by maternal weight and mode of delivery. Am J Clin Nutr, 2012; 96(3):544–551.

21.

Le Doare

, Holder

, Bassett

, Pannaraj

. Mother's milk: A purposeful contribution to the development of the infant microbiota and immunity. Front Immunol, 2018; 9:361.

22.

Jost

, Lacroix

, Braegger

, et al. Vertical mother–neonate transfer of maternal gut bacteria via breastfeeding. Environ Microbiol, 2014; 16(9):2891–2904.

23.

Pannaraj

, Li

, Cerini

, et al. Association between breast milk bacterial communities and establishment and development of the infant gut microbiome. JAMA Pediatr, 2017; 171(7):647–654.

24.

Duranti

, Lugli

, Mancabelli

, et al. Maternal inheritance of bifidobacterial communities and bifidophages in infants through vertical transmission. Microbiome, 2017; 5(1):66.

25.

Fehr

, Moossavi

, Sbihi

, et al. Breastmilk feeding practices are associated with the co-occurrence of bacteria in mothers' milk and the infant gut: The CHILD Cohort Study. Cell Host Microbe, 2020; 28(2):285.e284–297.e284.

26.

, Yan

, Wang

, et al. Distinct gut microbiota and metabolite profiles induced by different feeding methods in healthy chinese infants. Front Microbiol, 2020; 11:714.

27.

Penders

, Vink

, Driessen

, et al. Quantification of Bifidobacterium spp., Escherichia coli and Clostridium difficile in faecal samples of breast-fed and formula-fed infants by real-time PCR. FEMS Microbiol Lett, 2005; 243(1):141–147.

28.

Bezirtzoglou

, Tsiotsias

, Welling

. Microbiota profile in feces of breast- and formula-fed newborns by using fluorescence in situ hybridization (FISH). Anaerobe, 2011; 17(6):478–482.

29.

Bäckhed

, Roswall

, Peng

, et al. Dynamics and stabilization of the human gut microbiome during the first year of life. Cell Host Microbe, 2015; 17(5):690–703.

30.

Wang

, Li

, Wu

, et al. Fecal microbiota composition of breast-fed infants is correlated with human milk oligosaccharides consumed. J Pediatr Gastroenterol Nutr, 2015; 60(6):825–833.

31.

, Li

, Lee-Sarwar

, et al. Meta-analysis of effects of exclusive breastfeeding on infant gut microbiota across populations. Nat Commun, 2018; 9(1):4169.

32.

Biagi

, Quercia

, Aceti

, et al. The bacterial ecosystem of mother's milk and infant's mouth and gut. Front Microbiol, 2017; 8:1214.

33.

Milani

, Duranti

, Bottacini

, et al. The first microbial colonizers of the human gut: Composition, activities, and health implications of the infant gut microbiota. Microbiol Mol Biol Rev, 2017; 81(4):e00036-00017.

34.

Dzidic

, Collado

, Abrahamsson

, et al. Oral microbiome development during childhood: An ecological succession influenced by postnatal factors and associated with tooth decay. ISME J, 2018; 12(9):2292–2306.

35.

Damaceno

, Gallotti

, Reis

IMM

, et al. Isolation and identification of potential probiotic bacteria from human milk. Probiot Antimicrob Proteins 2021. [Epub ahead of print]; doi: 10.1007/s12602-021-09866-5

36.

Damaceno

, Souza

, Nicoli

, et al. Evaluation of potential probiotics isolated from human milk and colostrum. Probiot Antimicrob Proteins, 2017; 9(4):371–379.

37.

Murphy

, Curley

, O'Callaghan

, et al. The composition of human milk and infant faecal microbiota over the first three months of life: A pilot study. Sci Rep, 2017; 7:40597.

38.

Pärnänen

, Karkman

, Hultman

, et al. Maternal gut and breast milk microbiota affect infant gut antibiotic resistome and mobile genetic elements. Nat Commun, 2018; 9(1):3891.

39.

Simpson

, Avershina

, Storrø

, et al. Breastfeeding-associated microbiota in human milk following supplementation with Lactobacillus rhamnosus GG, Lactobacillus acidophilus La-5, and Bifidobacterium animalis ssp. lactis Bb-12. J Dairy Sci, 2018; 101(2):889–899.

40.

Tuominen

, Rautava

, Collado

, et al. HPV infection and bacterial microbiota in breast milk and infant oral mucosa. PLoS One, 2018; 13(11):e0207016.

41.

Yan

, Luo

, Zhang

, et al. Association and occurrence of bifidobacterial phylotypes between breast milk and fecal microbiomes in mother–infant dyads during the first 2 years of life. Front Microbiol, 2021; 12:669442.

42.

Wan

, Jiang

, Lu

, et al. Human milk microbiota development during lactation and its relation to maternal geographic location and gestational hypertensive status. Gut Microbes, 2020; 11(5):1438–1449.

43.

Lyons

, Shea

C-AO

, Grimaud

, et al. The human milk microbiome aligns with lactation stage and not birth mode. Sci Rep, 2022; 12(1):5598.

44.

Bardanzellu

, Fanos

, Reali

. “Omics” in human colostrum and mature milk: Looking to old data with new eyes. Nutrients, 2017; 9(8):843.

45.

Fernández

, Rodríguez

. Human milk microbiota: Origin and potential uses. Nestle Nutr Inst Workshop Ser, 2020; 94:75–85.

46.

Asnicar

, Manara

, Zolfo

, et al. Studying vertical microbiome transmission from mothers to infants by strain-level metagenomic profiling. mSystems, 2017; 2(1):e00164-16.

47.

Jost

, Lacroix

, Braegger

, Chassard

. Assessment of bacterial diversity in breast milk using culture-dependent and culture-independent approaches. Br J Nutr, 2013; 110(7):1253–1262.

48.

Perez

, Doré

, Leclerc

, et al. Bacterial imprinting of the neonatal immune system: Lessons from maternal cells?. Pediatrics, 2007; 119(3):e724–e732.

49.

Collado

, Delgado

, Maldonado

, Rodríguez

. Assessment of the bacterial diversity of breast milk of healthy women by quantitative real-time PCR. Lett Appl Microbiol, 2009; 48(5):523–528.

50.

Hunt

, Foster

, Forney

, et al. Characterization of the diversity and temporal stability of bacterial communities in human milk. PLoS One, 2011; 6(6):e21313.

51.

Martı´n

, Langa

, Reviriego

, et al. The commensal microflora of human milk: New perspectives for food bacteriotherapy and probiotics. Trends Food Sci Technol, 2004; 15(3):121–127.

52.

Kordy

, Gaufin

, Mwangi

, et al. Contributions to human breast milk microbiome and enteromammary transfer of Bifidobacterium breve. PLoS One, 2020; 15(1):e0219633.

53.

McGuire

, McGuire

. Got bacteria? The astounding, yet not-so-surprising, microbiome of human milk. Curr Opin Biotechnol, 2017; 44:63–68.

54.

Andres

, Scottoline

, Good

. Shaping infant development from the inside out: Bioactive factors in human milk. Semin Perinatol, 2023; 47(1):151690.

55.

Albesharat

, Ehrmann

, Korakli

, et al. Phenotypic and genotypic analyses of lactic acid bacteria in local fermented food, breast milk and faeces of mothers and their babies. Syst Appl Microbiol, 2011; 34(2):148–155.

56.

Kumar

, du Toit

, Kulkarni

, et al. Distinct patterns in human milk microbiota and fatty acid profiles across specific geographic locations. Front Microbiol, 2016; 7:1619.

57.

Padilha

, Danneskiold-Samsøe

, Brejnrod

, et al. The human milk microbiota is modulated by maternal diet. Microorganisms, 2019; 7(11):502.

58.

Williams

, Carrothers

, Lackey

, et al. Human milk microbial community structure is relatively stable and related to variations in macronutrient and micronutrient intakes in healthy lactating women. J Nutr, 2017; 147(9):1739–1748.

59.

Zimmermann

, Curtis

. Breast milk microbiota: A review of the factors that influence composition. J Infect, 2020; 81(1):17–47.

60.

Drago

, Toscano

, De Grandi

, et al. Microbiota network and mathematic microbe mutualism in colostrum and mature milk collected in two different geographic areas: Italy versus Burundi. ISME J, 2017; 11(4):875–884.

61.

Dao

, Zhang

, Wang

. Analysis of human milk fatty acid composition and its correlation with diet pattern (A study in Tibetan population gathering area). J Food Comp Analysis, 2023; 116:105046.

62.

Keikha

, Shayan-Moghadam

, Bahreynian

, Kelishadi

. Nutritional supplements and mother's milk composition: A systematic review of interventional studies. Int Breastfeed J, 2021; 16(1):1.

63.

Burianova

, Bronsky

, Pavlikova

, et al. Maternal body mass index, parity and smoking are associated with human milk macronutrient content after preterm delivery. Early Hum Dev, 2019; 137:104832.

64.

Aparicio

, Ocón

, Diaz-Castro

, et al. Influence of a concurrent exercise training program during pregnancy on colostrum and mature human milk inflammatory markers: Findings from the GESTAFIT Project. J Hum Lact, 2018; 34(4):789–798.

65.

Juncker

, Naninck

EFG

, Schipper

, et al. Maternal stress in the postpartum period is associated with altered human milk fatty acid composition. Clin Nutr, 2022; 41(11):2517–2528.

66.

Khodayar-Pardo

, Mira-Pascual

, Collado

, Martínez-Costa

. Impact of lactation stage, gestational age and mode of delivery on breast milk microbiota. J Perinatol, 2014; 34(8):599–605.

67.

Urbaniak

, Angelini

, Gloor

, Reid

. Human milk microbiota profiles in relation to birthing method, gestation and infant gender. Microbiome, 2016; 4:1.

68.

Hermansson

, Kumar

, Collado

, et al. Breast milk microbiota is shaped by mode of delivery and intrapartum antibiotic exposure. Front Nutr, 2019; 6:4.

69.

Moossavi

, Sepehri

, Robertson

, et al. Composition and variation of the human milk microbiota are influenced by maternal and early-life factors. Cell Host Microbe, 2019; 25(2):324.e324–335.e324.

70.

Galante

, Milan

, Reynolds

, et al. Sex-specific human milk composition: The role of infant sex in determining early life nutrition. Nutrients, 2018; 10(9):1194.

71.

Tottman

, Oliver

, Alsweiler

, Cormack

. Do preterm girls need different nutrition to preterm boys? Sex-specific nutrition for the preterm infant. Pediatr Res, 2021; 89(2):313–317.

72.

Quinn

. No evidence for sex biases in milk macronutrients, energy, or breastfeeding frequency in a sample of Filipino mothers. Am J Phys Anthropol, 2013; 152(2):209–216.

73.

Powe

, Knott

, Conklin-Brittain

. Infant sex predicts breast milk energy content. Am J Hum Biol, 2010; 22(1):50–54.

74.

Fujita

, Roth

, Lo

, et al. In poor families, mothers' milk is richer for daughters than sons: a test of Trivers-Willard hypothesis in agropastoral settlements in Northern Kenya. Am J Phys Anthropol, 2012; 149(1):52–59.

75.

Hahn

, Song

, Kang

. Do gender and birth height of infant affect calorie of human milk? An association study between human milk macronutrient and various birth factors. J Matern Fetal Neonatal Med, 2017; 30(13):1608–1612.

76.

Fields

, George

, Williams

, et al. Associations between human breast milk hormones and adipocytokines and infant growth and body composition in the first 6 months of life. Pediatr Obes, 2017; 12(Suppl. 1):78–85.

77.

Alur

, Ramarao

. Sex differences in preterm nutrition and growth: the evidence from human milk associated studies. J Perinatol, 2022; 42(8):987–992.

78.

Thakkar

, Giuffrida

, Cristina

, et al. Dynamics of human milk nutrient composition of women from Singapore with a special focus on lipids. Am J Hum Biol, 2013; 25(6):770–779.

79.

Baldeón

, Zertuche

, Flores

, Fornasini

. Free amino acid content in human milk is associated with infant gender and weight gain during the first four months of lactation. Nutrients, 2019; 11(9):2239.

80.

Hosseini

, Valizadeh

, Hosseini

, et al. The role of infant sex on human milk composition. Breastfeed Med, 2020; 15(5):341–346.

81.

The Effect of Infant's Sex on Human Milk Macronutrients Content: An Observational Study. Breastfeed Med, 2020; 15(9):568–571.

82.

Solís

, de Los Reyes-Gavilan

, Fernández

, et al. Establishment and development of lactic acid bacteria and bifidobacteria microbiota in breast-milk and the infant gut. Anaerobe, 2010; 16(3):307–310.

83.

Boix-Amorós

, Collado

, Mira

. Relationship between milk microbiota, bacterial load, macronutrients, and human cells during lactation. Front Microbiol, 2016; 7:492.

84.

Sakwinska

, Moine

, Delley

, et al. Microbiota in breast milk of Chinese Lactating Mothers. PLoS One, 2016; 11(8):e0160856.

85.

Dobler

, Dowling

, Morrow

, Reinhardt

. A systematic review and meta-analysis reveals pervasive effects of germline mitochondrial replacement on components of health. Hum Reprod Update, 2018; 24(5):519–534.

86.

Miklavcic

, Flaman

. Personhood status of the human zygote, embryo, fetus. Linacre Q, 2017; 84(2):130–144.

87.

Cyranoski

. The CRISPR-baby scandal: What's next for human gene-editing. Nature, 2019; 566(7745):440–442.

88.

Moubareck

. Human milk microbiota and oligosaccharides: A glimpse into benefits, diversity, and correlations. Nutrients 29, 2021; 13(4):1123.

89.

González

, Maldonado

, Martín

, et al. Breast milk and gut microbiota in African mothers and infants from an area of high HIV prevalence. PLoS One, 2013; 8(11):e80299.

90.

Haddad

, Sugino

, Kerver

, et al. The infant gut microbiota at 12 months of age is associated with human milk exposure but not with maternal pre-pregnancy body mass index or infant BMI-for-age z-scores. Curr Res Physiol, 2021; 4:94–102.

91.

Robinson

, Josefson

, Van Horn

. Considerations for preterm human milk feedings when caring for mothers who are overweight or obese. Adv Neonatal Care, 2019; 19(5):361–370.

92.

Demmelmair

, Jiménez

, Collado

, et al. Maternal and perinatal factors associated with the human milk microbiome. Curr Dev Nutr, 2020; 4(4):nzaa027.

93.

Fernández

, Langa

, Martín

, et al. The human milk microbiota: Origin and potential roles in health and disease. Pharmacol Res, 2013; 69(1):1–10.

94.

Heikkilä

, Saris

. Inhibition of Staphylococcus aureus by the commensal bacteria of human milk. J Appl Microbiol, 2003; 95(3):471–478.

95.

Espinosa-Martos

, Jiménez

, de Andrés

, et al. Milk and blood biomarkers associated to the clinical efficacy of a probiotic for the treatment of infectious mastitis. Benef Microbes, 2016; 7(3):305–318.

96.

Jiménez

, Fernández

, Maldonado

, et al. Oral administration of Lactobacillus strains isolated from breast milk as an alternative for the treatment of infectious mastitis during lactation. Appl Environ Microbiol, 2008; 74(15):4650–4655.

97.

Bayram

, Yavuz

, Benek

, et al. Effect of breast milk calcium and fluidity on breast cancer cells: An in vitro cell culture study. Breastfeed Med, 2016; 11:474–478.

98.

Roche-Hakansson

, Vansarla

, Marks

, Hakansson

. The human milk protein-lipid complex HAMLET disrupts glycolysis and induces death in Streptococcus pneumoniae. J Biol Chem 20, 2019; 294(51):19511–19522.

99.

Storm

, Aits

, Puthia

, et al. Conserved features of cancer cells define their sensitivity to HAMLET-induced death; c-Myc and glycolysis. Oncogene, 2011; 30(48):4765–4779.

100.

Brisuda

, Ho

JCS

, Kandiyal

, et al. Bladder cancer therapy using a conformationally fluid tumoricidal peptide complex. Nat Commun, 2021; 12(1):3427.

101.

García-Ricobaraza

, García-Santos

, Escudero-Marín

, et al. Short- and long-term implications of human milk microbiota on maternal and child health. Int J Mol Sci, 2021; 22(21):11866.

102.

LeMay-Nedjelski

, Yonemitsu

, Asbury

, et al. Oligosaccharides and microbiota in human milk are interrelated at 3 months postpartum in a cohort of women with a high prevalence of gestational impaired glucose tolerance. J Nutrit, 2021; 151(11):3431–3441.

103.

Collado

, Laitinen

, Salminen

, Isolauri

. Maternal weight and excessive weight gain during pregnancy modify the immunomodulatory potential of breast milk. Pediatr Res, 2012; 72(1):77–85.

104.

Villamil

, Rodríguez-Camejo

, Puyol

, et al. Immune profiling of breast milk from mothers with treated celiac disease. Pediatr Res, 2021; 89(3):488–495.

105.

Benítez-Páez

, Olivares

, Szajewska

, et al. Breast-milk microbiota linked to celiac disease development in children: A pilot study from the PreventCD Cohort. Front Microbiol, 2020; 11:1335.

106.

Olivares

, Albrecht

, De Palma

, et al. Human milk composition differs in healthy mothers and mothers with celiac disease. Eur J Nutr, 2015; 54(1):119–128.

107.

Olshan

, Zomorrodi

, Pujolassos

, et al. Microbiota and metabolomic patterns in the breast milk of subjects with celiac disease on a gluten-free diet. Nutrients, 2021; 13(7):2243.

108.

Roca

, Vriezinga

, Crespo-Escobar

, et al. Anti-gliadin antibodies in breast milk from celiac mothers on a gluten-free diet. Eur J Nutr, 2018; 57(5):1947–1955.

109.

Lyimo

, Howell

, Balandya

, et al. Innate factors in human breast milk inhibit cell-free HIV-1 but not cell-associated HIV-1 infection of CD4+ cells. JAIDS J Acquir Immune Defic Syndr, 2009; 51(2):117–124.

110.

Kuhn

, Trabattoni

, Kankasa

, et al. HIV-specific secretory IgA in breast milk of HIV-positive mothers is not associated with protection against HIV transmission among breast-fed infants. J Pediatr, 2006; 149(5):611–616.

111.

Bender

, Li

, Martelly

, et al. Maternal HIV infection influences the microbiome of HIV-uninfected infants. Sci Transl Med, 2016; 8(349):349ra100–349ra100.

112.

Demers-Mathieu

, DaPra

, Mathijssen

, et al. Human milk antibodies against S1 and S2 subunits from SARS-CoV-2, HCoV-OC43, and HCoV-229E in mothers with a confirmed COVID-19 PCR, viral SYMPTOMS, and unexposed mothers. Int J Mol Sci, 2021; 22(4):1749.

113.

Davanzo

, Moro

, Sandri

, et al. Breastfeeding and coronavirus disease-2019: Ad interim indications of the Italian Society of Neonatology endorsed by the Union of European Neonatal & Perinatal Societies. Matern Child Nutr, 2020; 16(3):e13010.

114.

Spatz

, Davanzo

, Müller

, et al. Promoting and protecting human milk and breastfeeding in a COVID-19 world. Front Pediatr, 2021; 8:633700.

115.

Bäuerl

, Randazzo

, Sánchez

, et al. SARS-CoV-2 RNA and antibody detection in breast milk from a prospective multicentre study in Spain. Arch Dis Child Fetal Neonatal Ed, 2022; 107(2):216–221.

116.

Zhao

, Shang

, Ren

, et al. Omics study reveals abnormal alterations of breastmilk proteins and metabolites in puerperant women with COVID-19. Signal Transduct Target Ther, 2020; 5(1):247.

117.

Ebrahimi

, Khatami

, Mesdaghi

. The effect of COVID-19 pandemic on the infants' microbiota and the probability of development of allergic and autoimmune diseases. Int Arch Allergy Immunol, 2022; 183(4):435–442.

118.

Kyle

, Glassman

, Khan

, et al. A review of newborn outcomes during the COVID-19 pandemic. Semin Perinatol, 2020; 44(7):151286.

119.

Laursen

, Bahl

, Licht

. Settlers of our inner surface—Factors shaping the gut microbiota from birth to toddlerhood. FEMS Microbiol Rev, 2021; 45(4):fuab001.

120.

Edwards

. Determinants and duration of impact of early gut bacterial colonization. Ann Nutr Metab, 2017; 70(3):246–250.

121.

Ferretti

, Pasolli

, Tett

, et al. Mother-to-infant microbial transmission from different body sites shapes the developing infant gut microbiome. Cell Host Microbe, 2018; 24(1):133.e135–145.e135.

122.

Moeller

, Suzuki

, Phifer-Rixey

, Nachman

. Transmission modes of the mammalian gut microbiota. Science, 2018; 362(6413):453–457.

123.

Drell

, Štšepetova

, Simm

, et al. The influence of different maternal microbial communities on the development of infant gut and oral microbiota. Sci Rep, 2017; 7(1):9940.

124.

Ejtahed

, Hasani-Ranjbar

. Neuromodulatory effect of microbiome on gut-brain axis; new target for obesity drugs. J Diabetes Metab Disord, 2019; 18(1):263–265.

125.

Mazloom

, Siddiqi

, Covasa

. Probiotics: How effective are they in the fight against obesity?. Nutrients, 2019; 11(2):258.

126.

Oddi

, Huber

, Rocha Faria Duque

, et al. Breast-milk derived potential probiotics as strategy for the management of childhood obesity. Food Res Int, 2020; 137:109673.

127.

Cacho

, Lawrence

. Innate immunity and breast milk. Front Immunol, 2017; 8:584.

128.

Carr

, Virmani

, Rosa

, et al. Role of human milk bioactives on infants' gut and immune health. Front Immunol, 2021; 12:604080.

129.

Marks

, Clementi

, Hakansson

. The human milk protein-lipid complex HAMLET sensitizes bacterial pathogens to traditional antimicrobial agents. PLoS One, 2012; 7(8):e43514.

130.

Henrick

, Rodriguez

, Lakshmikanth

, et al. Bifidobacteria-mediated immune system imprinting early in life. Cell, 2021; 184(15):3884.e3811–3898.e3811.

131.

Quin

, Vicaretti

, Mohtarudin

, et al. Influence of sulfonated and diet-derived human milk oligosaccharides on the infant microbiome and immune markers. J Biol Chem, 2020; 295(12):4035–4048.

132.

Gao

, Nanan

, Macia

, et al. The maternal gut microbiome during pregnancy and offspring allergy and asthma. J Allergy Clin Immunol, 2021; 148(3):669–678.

133.

Wei

, Jiang

, Liu

, et al. Association between probiotic supplementation and asthma incidence in infants: A meta-analysis of randomized controlled trials. J Asthma, 2020; 57(2):167–178.

134.

Cait

, Cardenas

, Dimitriu

, et al. Reduced genetic potential for butyrate fermentation in the gut microbiome of infants who develop allergic sensitization. J Allergy Clin Immunol, 2019; 144(6):1638.e1633–1647.e1633.

135.

Zuurveld

, van Witzenburg

, Garssen

, et al. Immunomodulation by human milk oligosaccharides: The potential role in prevention of allergic diseases. Front Immunol, 2020; 11:801.

136.

Jakaitis

, Denning

. Human breast milk and the gastrointestinal innate immune system. Clin Perinatol, 2014; 41(2):423–435.

137.

Maffei

, Schanler

. Human milk is the feeding strategy to prevent necrotizing enterocolitis! Semin Perinatol 2017;41(1):36–40.

138.

Wejryd

, Martí

, Marchini

, et al. Low diversity of human milk oligosaccharides is associated with necrotising enterocolitis in extremely low birth weight infants. Nutrients, 2018; 10(10):1556.

139.

Donovan

. Role of human milk components in gastrointestinal development: Current knowledge and future NEEDS. J Pediatr, 2006; 149(5, Suppl.):S49–S61.

140.

Girbovan

, Sur

, Samasca

, Lupan

. Is the evidence of breast feeding protection against coeliac disease real?. Allergol Immunopathol, 2017; 45(6):616–618.

141.

Henriksson

, Boström

, Wiklund

. What effect does breastfeeding have on coeliac disease? A systematic review update. Evid Based Med, 2013; 18(3):98–103.

142.

Cilleruelo

, Fernández-Fernández

, Jiménez-Jiménez

, et al. Prevalence and natural history of celiac disease in a cohort of at-risk children. J Pediatr Gastroenterol Nutr, 2016; 62(5):739–745.

143.

Sanjulián

, Lamas

, Barreiro

, et al. Bacterial diversity of breast milk in Healthy Spanish Women: Evolution from birth to five years postpartum. Nutrients, 2021; 13(7):2414.

144.

Lackey

, Williams

, Meehan

, et al. What's normal? Microbiomes in human milk and infant feces are related to each other but vary geographically: The INSPIRE Study. Front Nutr, 2019; 6:45.

145.

Ruiz

, Alba

, García-Carral

, et al. Comparison of two approaches for the metataxonomic analysis of the human milk microbiome. Front Cell Infect Microbiol, 2021; 11:622550.

146.

Dutta

, Das

, Ghosh

, et al. Human milk microbiome of healthy Indian mothers is dominated by genus pseudomonas. J Hum Lact, 2021; 39(2):343–352.

147.

LeMay-Nedjelski

, Butcher

, Ley

, et al. Examining the relationship between maternal body size, gestational glucose tolerance status, mode of delivery and ethnicity on human milk microbiota at three months post-partum. BMC Microbiol, 2020; 20(1):219.

148.

Butts

, Paturi

, Blatchford

, et al. Microbiota composition of breast milk from women of different ethnicity from the Manawatu—Wanganui Region of New Zealand. Nutrients, 2020; 12(6):1756.

149.

Kim

, Joung

, Kang

D-K

, et al. Anti-obesity effects of Lactobacillus rhamnosus 4B15, and its synergy with hydrolysed lactose skim milk powder. Int Dairy J, 2021; 123:104997.