Advantages of breastfeeding for the mother-infant dyad

INTRODUCTION

A child’s feeding plays a key role in its health and development both during infancy and later in life. Breastfeeding is a natural way of feeding infants, providing all the necessary nutrients, growth factors, bioactive molecules, as well as antibodies and immunological factors supporting the development of the immune system. Breastfed infants are less likely to suffer from metabolic disorders, including obesity and diabetes, later in life, and are characterised by better cognitive development. Breastfeeding also has a beneficial effect on the mother’s health, reducing the risk of cancer, obesity, and other cardiometabolic disorders [1]. Modified milk feeding, often called formula feeding, involves feeding an infant a specially formulated product that attempts to mimic the composition of the breast milk, but is based on cow’s and/or other animal milk, or other ingredients, which are suitable for infant feeding. Feeding with modified milk may be necessary for mothers who face specific medical and social issues, or due to the specific health needs of the baby. The formulas are classified based on caloric density, carbohydrate source, and protein composition. All types of formulas should meet the standards adopted by the Codex Alimentarius Commission (CAC), which is the central part of the Joint FAO/WHO Food Standards Programme [2].
This article provides an overview of the advantages of breastfeeding for infants and their mothers according to the current state of knowledge.

DATA SOURCE

We searched PubMed and Google Scholar databases using the major keywords: ‘breastfeeding’, ‘formula feeding’, ‘human breast milk’, ‘advantages of breastfeeding’, ‘maternal health’, and ‘infant health’. The other key words used for searching are presented in Diagram 1. Selection and eligibility criteria were based on the title and content of abstracts, exclusion of case reports, conference abstracts, letters, and editorial articles. Based on the number of citations and journal impact factor, we limited our search to the most essential and current publications, including observational studies, clinical trials, and meta-analysis studies in the English language. After screening articles, we ended up with 63 articles that were relevant to our paper.

IMPACT OF BREASTFEEDING ON CHILD HEALTH

Breast milk is ideally suited to the needs of the developing infant, providing an adequate caloric load and easily digestible forms of nutrients, growth and immune factors. Therefore, exclusive feeding with human milk for the first 6 months of life, with continued breastfeeding, together with complementary foods, up to 2 years of age or beyond, remains the preferred mode of infant feeding [3, 4].

HUMAN BREAST MILK AS AN OPTIMAL NUTRITION

Human breast milk nutrients are easily digestible and highly absorbable. There are several factors present in a human milk that contribute to this favourable situation: high-quality proteins in the form of easily digestible peptides and amino acids, the right proportions of different types of fats (e.g. omega-3 and omega-6 acids), the pre­sence of digestive enzymes supporting digestion of fats and carbohydrates, the presence of lactose, which facilitates the absorption of calcium, and the presence of lacto­ferrin and vitamin C, which increase the absorption of iron.
The main nutritional and non-nutritional components of human milk include the following:
• Proteins: casein, α-lactalbumin, lactoferrin, lactadhe­rin, CCL28 mucosal chemokine (C-C Motif Chemokine Ligand 28, CCL28), complement component 3 (C3) and fibronectin, serum albumin, lysozyme, defensins, and immunoglobulins, which play a key role in strengthening the infant’s immune system [5].
• Carbohydrates: mainly in the form of lactose, which is the main energy source for the growing infant’s body. Human milk oligosaccharides (HMOs) belong to the most abundant components of human milk. Although HMOs are non-nutritive to the infant, they play a crucial role as prebiotics preventing pathogen adhesion and modifying gut microbiota [5].
• Fats: in the form of saturated- (SFA), monounsaturated-(MUFA), and polyunsaturated fatty acids (PUFA). Although the latter represents only 15% of the total lipid load, their health-promoting function is unquestionable, because PUFAs are important for the deve­lopment of the infant’s brain and peripheral nervous system, retina, and immune system [6].
• Vitamins and minerals: A, C, D, E, K, B group, iron, calcium, zinc, iodine, and many others that are essential for the growth and development of the infant as they strengthen bones, heal wounds, boost the immune system, and repair cellular damage. They also partici­pate in haemopoiesis, haemostasis, neurodevelopment, and the conversion of food into energy. However, human milk contains low quantities of vitamins K and D. Therefore, to prevent disorders resulting from their insufficiency, current paediatric recommendations indicate the necessity of postnatal vitamin D and K supplementation of breastfed infants [7].
• Hormones and growth factors: these support the development and growth of the child’s organs (e.g. insulin, insulin-like growth factor [IGF], growth hormone [GH], epidermal growth factor [EGF], fibroblast basic growth factor [FBGF], hepatocyte growth factor [HGF], nerve growth factor [NGF], and erythropoietin [EPO]), control metabolic functions, and participate in the programming of energy balance regulation in childhood (e.g. insulin, ghrelin, leptin, resistin, and adiponectin) [8]. Human milk hormones also have immune effects (e.g. cytokines and chemokines activating Th1- and Th2-responses or playing roles as regulatory and immunoregulatory factors) [9].
• Prebiotics: HMOs, glycans, and other bioactive components, including mucins, promote the development of a healthy microbiome in the infant’s digestive tract that benefits the immune system, digestion, and brain-gut axis [5].
It is worth noting that the nutritional composition of breast milk can change depending on several factors, such as the mother’s age, diet, health status, and stage of lactation. Additionally, it has been shown that breastfeeding is characterised by the daily changes of human milk composition. Various components, including fats, individual amino acids, iron, cortisol, or melatonin, exhibit daily fluctuations that may contribute to the synchronisation of the child’s metabolism and maturation of the internal circadian system [10]. This type of chrononutrition is obviously not present in formula-fed infants.

IMMUNE-BOOSTING PROPERTIES OF HUMAN MILK

Breast milk contains antibodies that are transferred from mother to child. The most important immunoglobulins in breast milk are IgA, IgG, and IgM. IgA plays a key role in protecting mucous membranes (via neutralisation of microorganisms and inhibition of their adhesion to host cells) in the respiratory tract and gastrointestinal system, which are the main entry routes for pathogens. Breast milk also contains various immunological factors, such as glycoproteins and cytokines. The major glycoproteins, such as lactoferrin and lactadherin, can participate in innate immunity by blocking pathogen adhesion to host cells and protecting immature infants against infection and excessive inflammatory response. Lactoferrin exhibits antibacterial, antiviral, antifungal, and antiparasitic properties, while lactadherin protects from rotavirus infection and accelerates healing of the intestinal injury in infants [9]. Lysozyme, another glycoprotein in human milk, demonstrates bacteriolytic properties destroying bacterial walls with particularly strong activity against gram-positive bacteria. Lysozyme is also known to have antiviral and anti-inflammatory properties [9]. Human milk cytokines act as potent messengers influencing the immune activity of the infant body. The most abundant anti-inflammatory cytokines in the breast milk are IL-4, IL-7, IL-10, IL-13, IL-18, growth transforming factor β (TGF–β), and granulocyte-colony stimulating factor (GCSF), while inflammatory cytokines include IL-2, IL-5, IL-6, IL-8, IL-12, interferon γ (INFγ), and tumour necrosis factor α (TNF-α) [5, 10].
Human breast milk contains various immune-competent cells that contribute to both innate (macrophages and neutrophils, NK cells) and adaptive immunity (CD8+ and CD4+ T cells, B cells, plasma cells). Additionally, under physiologic conditions, human milk contains up to 4 log10 colony-forming units (cfu)/mL bacteria, which facilitate the establishment of the “healthy” and diverse gut microbiota. The 2 species Bifidobacterium and Lactobacillus are particularly important because of their potential probiotic roles. They modulate immune response via improvement of intestinal barrier function, competitive pathogen exclusion from gut epithelia, direct production of antimicrobial factors, or interaction with immune cells. Therefore, they may participate in the treatment of various infectious, allergic, and inflammatory conditions such as diarrhoea due to viral or bacterial infections [11].
Human breast milk is a rich source of circulating microRNA (miRNA) that can exert beneficial regulatory function in diverse gene expression, cell growth, metabolism, and immunity [12].

BREAST MILK AND THE RISK OF ALLERGY AND FOOD INTOLERANCE

Research has shown that proteins present in human breast milk have low allergenic potential; however, small amounts of food protein from the mother’s diet may pass through into breast milk. Even though food proteins in human milk can trigger allergic reactions in infants with IgE-mediated food allergies, the probability of an IgE-mediated allergic reaction is low [13]. For infants who are genetically predisposed to food allergies, less allergenic proteins play a key role in shaping immune tolerance, which may help to reduce the risk of food allergies. Antibodies present in breast milk, especially IgA, participate in protecting the infant’s gastrointestinal tract from excessive activation of the immune system in response to food antigens. Additionally, HMOs promote the development of the mucosal immune system and colonic microbiota of the infant [14]. However, some researchers indicate that, depending on individual variations in breast milk composition, the allergy-preventing effect of breastfeeding may vary from one mother to another.
Based on a recently published study, low-grade quality evidence exists that longer duration of breastfeeding is associated with (1) reduced risk of asthma in children aged 5–18 years, (2) reduced risk of allergic rhinitis in children up to 5 years of age, and reduced risk of eczema in children up to 2 years of age [15]. The latest clinical report from the American Academy of Pediatrics on the prevention of an infant atopic disease states that exclusive breastfeeding for 3 to 4 months reduces the incidence of eczema in the first 2 years of life, while there is no short- or long-term benefit of exclusive breastfeeding beyond 3 to 4 months in preventing atopic disease. In addition, any period of breastfeeding ≥ 3 to 4 months protects against wheezing in the first 2 years of life, and some evidence suggests that longer breastfeeding protects against asthma even after 5 years of age. Also, no conclusions can be drawn about the role of breastfeeding in preventing or delaying the onset of specific food allergies [15].
Similar findings apply to the Australasian Society of Clinical Immunology and Allergy (ASCIA) guidelines: Infant Feeding and Allergy Prevention, which states that breastfeeding during the period from around 6 months may help reduce the risk of the infant developing allergies, although evidence for this is low [16].
It is worth remembering that the risk of allergies and food intolerances is complex and can be triggered by various genetic, environmental, and dietary factors.

BREAST MILK AND NERVOUS SYSTEM DEVELOPMENT

Breast milk feeding has a beneficial effect on infants’ brain and nervous system development [17]. Factors that benefit brain and nervous system development refer to the following:
• Omega-3 fatty acids, especially docosahexaenoic acid (DHA) and omega-6 fatty acids, e.g. arachidonic acid. DHA is a key structural component of the brain and retina. Providing sufficient DHA through breast milk can support normal brain development, including thought processes, memory, visual perception, and cognitive function in infants.
• Phospholipids that are essential for the proper functioning of nerve cells, nerve transmission, and the synthesis and transport of neurotransmitters.
• Growth factors, including nerve growth factor (NGF) and insulin-like growth factor I (IGF-1), which influence neurogenesis and the processes associated with neuronal plasticity.
• Micronutrients, such as iron, zinc, copper, and selenium that are essential for brain and nervous system development, neural transmission, and metabolism.
• Bioactive molecules, including miRNA, carotenoids, choline, taurine, and carnosine, that affect nervous system structure and function (e.g. carotenoids, especially lutein, can improve neuronal transmission and protect neurons against oxidative damage; choline is a precursor of neurotransmitters and a structural component of cell membranes).
However, because randomised trials comparing the impact of breastfeeding with formula feeding on neuro-development cannot be done, many confounding variables must be taken into consideration (e.g. maternal and paternal IQ, social status, educational level, stress, child variables, and abnormal neurologic testing). Therefore, it is hard to clearly conclude that breastfeeding significantly improves developmental and cognitive outcomes. The exception is the neurodevelopmental advantage in premature infants fed breast milk [18].

BREAST MILK LOWERS THE RISK OF OBESITY AND CHRONIC DISEASES LATER IN LIFE

Breastfeeding is associated with a lower risk of obesity and chronic diseases in childhood and later in life. Breastfeeding allows the infant to control its food intake, which promotes proper regulation of appetite and satiety. Breastfed infants tend to consume an amount of food according to their actual needs, which can reduce the risk of food overconsumption, unhealthy feeding patterns, and obesity in later life. Moreover, there is an association between a longer duration of breastfeeding and a lower risk of overweight and obesity in childhood and adulthood [19].
Breastfeeding is associated with more favourable levels of hormones responsible for appetite regulation, metabolism, and energy management. This can contri­bute to maintaining a healthy phenotype and normal body weight of the baby. It has been shown that fasting insulin and the risk of insulin resistance are reduced in both breastfed children and their mothers [20], while leptin concentrations remain elevated in breastfed infants, which partially depends on its presence in human milk [21]. Leptin in its normal concentrations works as a satiety factor that strongly participates in signalling whole-body energy balance and metabolic functions, including the inhibition of appetite and prevention of hyperinsulinaemia [21]. Although the leptin level correlates with anthropometric parameters, its direct effect on children’s body weight later in life is not fully understood [22].
The nutritional programming of healthy body weight and metabolic balance is also associated with the bacterial diversity of an infant’s gut microbiota. Knowing that dysbiosis during infancy is related to obesity later in life [23], it is worth remembering that breast milk contains prebiotics, which promote the development of a healthy microbiome in the infant’s intestines.
All these factors contribute to the lower risk of obesity and obesity-related chronic diseases such as insulin resistance, type 2 diabetes, coronary artery disease, hypertension, and some types of cancer.

BREAST MILK LOWERS THE RISK OF CANCER

Human breast milk contains anticancer components that may induce programmed cell death of tumour cells. Breast milk-derived cytotoxic protein-fatty acid complex, called HAMLET (human alpha-lactalbumin made lethal to tumour cells), which contains alpha-lactalbumin and oleic acid, accumulates in the nucleus, triggering an apoptosis of cancer cells [24]. The other substances capable of apoptotic signalling include TRAIL – a cytokine derived from colostrum (TNF-related apoptosis inducing ligand), human milk kappa-casein, and lactoferrin [25].

BREAST MILK PLAYS A ROLE AS AN EPIGENETIC REGULATOR OF HEALTH AND DISEASE

Studies have shown that breast milk participates in the removal of damaged DNA and in tissue repair. The following mechanisms are currently proposed to explain this beneficial effect:
Breast milk boosts the immune system, allowing for more efficient elimination of damaged cells and tissue regeneration.
Breast milk is rich in antioxidants, which help to combat the formation of reactive oxygen species (ROS) and oxidative stress, which modify the structure of DNA and induce DNA fragmentation [26]. Oxidation of DNA is highly mutagenic and may be the basis for mutations, carcinogenesis, apoptosis, necrosis, and hereditary diseases. Antioxidants in breastmilk include endogenous enzymes capable of eliminating free radicals (superoxide dismutase [SOD], catalase, glutathione peroxidase [GPx]), Glutathione system, food-derived antioxidants (e.g. vitamin E and vitamin C), and the major hormonal free radical scavenger – melatonin [27].
Circulating in breast milk, miRNA may participate in apoptosis or DNA repair [5].
Breast milk might influence DNA methylation through the effects of some of its nutritional components that contain methyl group (e.g. choline, folate, methionine). The process of DNA methylation and demethylation is one of the mechanisms that regulate gene expression, participate in the programming metabolic health of the offspring, and may affect the repair of damaged DNA. Based on an epigenome-wide association study (EWAS), several DNA islands have been identified as regions of the methylome associated with breastfeeding, including methylation in the cg11414913 CpG, or cg05800082 CpG [28], and genes involved in fat metabolism (RXRA), appetite control (LEP), growth and metabolism (IGF2), and maintenance of DNA methylation marks (DNMT1) [28]. It has been shown that obesity-related gene methylation status affects the link between breastfeeding and long-term outcomes, e.g. obesity development. Breastfeeding might be associated with methylation of the LEP (negatively), RXRA (positively), and IGF2 (negatively), modulating the gene expression level and lowering adiposity in young children and neonates [29].
Some of the bioactive proteins in breast milk, including lactoferrin, or growth factors, may show the ability to repair damaged DNA. Apart from indirect activities, lactoferrin directly affects transcription factors, gene expression, cell cycle, and differentiation, and it partici­pates in the elimination of cancer cells [30].
Human milk stem cells have the ability to differen­tiate into various cell lineages, including cells involved in the repair of damaged DNA [31]. Stem cells may also act as epigenetic regulators because they contain bioactive molecules, such as miRNA [7].

BREASTFEEDING HELPS TO PREVENT SUDDEN INFANT DEATH SYNDROME (SIDS)

Although observational studies cannot prove causation and randomised trials cannot be done, the strong association between breastfeeding and significantly reduced risk of SIDS has been confirmed [32]. Better immunity and fewer infections affecting the respiratory system as well as being a light sleeper are the 2 po­stulated mechanisms related to breastfeeding’s protective role [32].

IMPACT OF NATURAL FEEDING ON MATERNAL HEALTH

BREASTFEEDING HELPS MOTHERS TO RECOVER AFTER DELIVERY

Breastfeeding has a positive effect on uterine involution and the reduction of postpartum bleeding. Breastfeeding, via breast-brain neuroendocrine reflex, stimulates the hypothalamic production of oxytocin, which promotes the uterus contractions and speeds up its involution process. Additionally, intense uterus contractions participate in the constriction of the blood vessels where the placenta has been detached, which reduces excessive postpartum bleeding and iron loss.

BREASTFEEDING REDUCES THE RISK OF BREAST, OVARIAN, AND ENDOMETRIAL CANCER

Breastfeeding is associated with a reduced risk of the most lethal type of ovarian cancer (OC) – a high-grade serous cancer. Interestingly, longer duration of breastfeeding and older age at the first and last breastfeeding episode are both inversely related to the risk of OC [33].
There are many factors and mechanisms that possibly contribute to this beneficial relationship:
• Breastfeeding leads to the reflex suppression of pitui­tary gonadotropins, especially luteinising hormone (LH), which is considered to be a one of the potential causal mechanisms of OC [34]. Moreover, inhibition of LH caused by breastfeeding suppresses ovulatory cycles and ovulation-induced trauma, apoptosis, and regenerative repair at the site of ovulation. In regularly ovulating women these processes predispose ovarian surface epithelial cells to carcinogenesis [34].
• Decreased number of lifetime ovulatory cycles limits the exposure of healthy cells to oestrogens, which are known to exhibit genotoxic and mitogenic effects [35].
• High levels of oxytocin protect against cancer because oxytocin exhibits anti-proliferative, anti-migratory, and anti-invasive properties possibly via anti-inflammatory mechanisms [36].
• Breast milk demonstrates anticancer properties with the use of anti-infective, antioxidant, immunomodulatory, and anti-inflammatory factors. Some of them specifically promote programmed tumour cell death (e.g. HAMLET or TRAIL) providing effective protection against the development of breast cancer [24, 25].

BREASTFEEDING FACILITATES POSTPARTUM WEIGHT LOSS

Most studies report that natural feeding has a positive effect on postpartum weight loss, playing a protective role against obesity/overweight and obesity-related diseases. During the first 6 months postpartum, exclusively breastfeeding mothers, as compared with formula-and mixed-feeders, benefit significantly more from decreasing postpartum weight [37]. This beneficial effect may result from the following:
• Extra energy expenditure. The average energy cost for milk production accounts for about 25% of the resting energy requirement during lactation [38].
• Endocrine factors that favour lipolysis, and their combined action in the maternal organism. These include the following: decreased basal insulin levels, which is associated with lowered lipogenesis, mutual effects of prolactin and leptin on their secretion resulting in stimulated galactogenesis, energy expenditure (prolactin) and anorexigenic effect (leptin), decreased levels of cortisol, and increased secretion of brain cholecystokinin both resulting in appetite inhibition [20].
However, some studies reported a lack of association between breastfeeding and maternal weight [38]. Any discrepancies in this field are due to the mother’s physi­cal activity, genetics, diet, body weight before pregnancy and weight gained during pregnancy, caloric intake/restriction, and duration and intensity of breastfeeding.

PROTECTION AGAINST CARDIOMETABOLIC DISEASES AND OSTEOPOROSIS

Women who breastfeed may benefit from protection against the onset of ischaemic heart disease, hypertension, stroke, maternal type 2 diabetes, and rheumatoid arthritis [39, 40]. Regular breastfeeding may lower blood lipid levels, improve glucose metabolism and insulin sensitivity, reduce body weight, and exhibit anti-inflammatory properties, which translates into cardiovascular benefits.
Also, although the nursing mother’s body uses bone calcium reserves for milk production, breastfeeding may reduce the risk of osteoporosis in later life [41]. When the diet is adequately balanced in terms of calcium, the efficiency of calcium absorption and utilisation increases, which can contribute to bone strengthening.
However, some investigators indicated a negative association between the duration of breastfeeding and bone density in perimenopausal women [42], while others showed no significant impact [43]. These discrepancies may result from different designs of studies, duration of lactation, and different maternal factors such as age, parity, nutritional status and dietary behaviour, stage of menopausal transition, ethnicity, and others [44].

EMOTIONAL BENEFITS AND BONDING BETWEEN MOTHER AND CHILD

Breastfeeding enhances maternal-infant bonding and empathic behaviour and protects the mother from lowered mood and postpartum depression, possibly via strong anxiolytic and stress-reducing properties of oxytocin and prolactin [45]. In addition, during early motherhood (up to 6 months after delivery) exclusively breastfeeding women, when compared with formula feeders, are less fatigued and experience better sleep patterns [46].

EFFECT OF FEEDING MODIFIED MILK ON BABY’S HEALTH

Feeding with modified milk is a convenient solution to share feeding responsibilities between caregivers when maternal milk is unavailable. However, situations when formula feeding is recommended instead of breastfeeding are rare. According to the American Academy of Pediatrics, contraindications to breastfeeding include the following: infants with classic galactosaemia, mothers, in the US, who are infected with human immunodeficiency virus (HIV), untreated brucellosis, or suspected or confirmed Ebola virus disease, mothers using substances such as opioids, cocaine, and PCP (phencyclidine), mothers who are positive for human T-cell lymphotropic virus type I or II, mothers with active (infectious) untreated tuberculosis, and mothers with active herpes simplex lesions on the breast [47].
Modified milk attempts to mimic human breast milk composition, but it offers far fewer benefits than human breast milk and, therefore, could be accompanied by several health risks. The exception is vitamin K and vitamin D content, which is low in breast milk and sufficient in formulas [7]. Apart from being deficient in immune factors, formula feeding is associated with risks of severe infectious diseases because powdered infant formula is not a sterile product. Some of the pathogens contaminate formula milk during the manufacturing process and/or during formula preparation and storage at home [48]. As reported by health authorities, formula contamination with Salmonella enterica and/or Enterobacter sakazakii are of greatest concern because there is clear evidence of causality linking formula contamination with these bacteria with life-threating illness in infants [49].
on the volume of milk remaining in the bottle, formula feeding may give the impression of a perfect opportunity to monitor and adjust the amount of food according to the baby’s appetite and needs. However, several studies confirmed that the feeding method, among other factors shaping feeding behaviour, impacts feeding behaviours and patterns of hunger [50]. Formula-fed infants experience rapid and often excessive weight gain due to dysregulation of hunger-satiety cues [51], while breastfeeding is related to greater appetite regulation and obesity-protective eating behaviours throughout childhood [52].

CONCLUSIONS

Breastfeeding is characterised by its unique health advantages for both mother and child. However, some mothers still decide to choose infant formula as an acceptable alternative. Therefore, extending the knowledge about the benefits of natural feeding is required.

DISCLOSURE

The authors report no conflict of interest.

References