Introduction
Doctors advise mothers to breastfeed their babies for at least six months due to its great benefits. In addition to being an amazing nutritive source, breast milk also has a crucial role in providing immunity to infants. Components in breast milk, such as cytokines, hormones, lipids, enzymes, etc., help in protecting and shaping the immune system of infants. Breast milk also consists of microbiota and provides resistance against various infections. Breastfeeding for the first 1,000 days may reduce risk factors and prevent disorders connected to metabolism and the immune system. Many short-term and long-term diseases, like obesity, asthma, type 2 diabetes, etc., can be prevented if the infants are breastfed. Hence, breast milk has been deemed the gold standard for newborn nutrition in the first several months after birth.
Studies found that factors such as geography, sex of the infant, and number of pregnancies can influence the composition of breast milk, which in turn can impact the shaping of the immune system in babies. The breastfeeding mother’s diet and lifestyle can also influence the immune system of infants.
How Does Breastfeeding Contribute to Immunity in Newborns?
Birth is a dramatic transition for newborns because they get exposed to a new environment with various microorganisms. In the first month of life, they are highly susceptible to infections. Fetal programming, a physiological process influenced by proper nutrition for mothers before and during pregnancy, controls how the fetus develops. Defects in this programming may make the newborns susceptible to non-communicable chronic diseases, which can be prevented by breastfeeding.
During fetal development, the maternal immune cells reach the fetal circulation through the placenta. After birth, newborns acquire maternal immune cells through breastfeeding. Studies found that the components of breast milk interact with the saliva of the newborn and protect the immune cells from the acidic pH of the stomach. Maternal antibodies, non-inherited maternal antigens (NIMA), and maternal leukocytes reach the intestine of infants through their stomachs. The immune and stem cells from the mother reach the infant’s bloodstream resulting in maternal microchimerism. This process produces immune intolerance in infants.
Recent studies have shown that breastmilk consists of natural killer cells, innate lymphoid cells, cytotoxic cells, T-regulatory cells, B cells, neutrophils, etc. These cells can produce bioactive molecules such as lactoferrin, lysozyme, cytokines, oligosaccharides, etc., which help provide active immunity to infants. Breast milk can help in the immunologic tolerance of infants to antigens from the mother and environment. This plays a role in achieving lifelong hemostasis (a physiological process to arrest bleeding) and prevents immune-related diseases.
Studies also found that the size of the thymus (a lymphoid organ situated in the upper chest and is a main part of the immune system) of breastfed infants is double that of non-breastfed infants. Extracellular vesicles in breast milk can also play a role in shaping the immune system. They can also positively influence gut health and prevent necrotizing enterocolitis in infants.
Do Maternal Antibodies Transfer to Breast Milk?
During the first week of life, the breast milk produced is called colostrum. It is golden yellow and has high nutritional value. So during the initial weeks of life, colostrum provides immunity to infants. IgA or immunoglobulin A is an antibody present in breast milk and is of two types; IgA1 and IgA2. IgA1 is present in the respiratory tract, serum, saliva, and skin, while IgA2 is in the intestine. IgA antibodies are continuously provided through breast milk. Selective IgGs are the natural antibodies produced in the mother's body in response to pathogens or immunization, which might affect the infant's humoral immune response.
How Does the Diet of a Breastfeeding Mother Alter the Immunity of the Baby?
Maternal nutrition can impact the composition of breastmilk, which in turn can affect the baby's immunity. The diet of the mother can have an influence on the composition of milk as well as the diversity of microbiota in breast milk. The microbiota in breast milk includes Streptococcus, Staphylococcus, Veillonella, Lactobacillus, etc. Formula milk does not promote innate and adaptive immunity and the development of gut microbes in infants. Sometimes this may lead to the development of a defective immune system which may not have resistance against various disease-causing microbes.
During pregnancy, if the mother eats food rich in fat and sugar, it can harm fetal programming and the composition of breast milk. Mothers who eat a diet rich in high fat may increase the inflammatory cytokines and SFB (segmented filamentous bacteria) colonization in infants' guts. Foods rich in fats, carbohydrates, and proteins can alter the composition of microbiota in breast milk by promoting the accumulation of Staphylococcus and Bifidobacterium. Whereas foods rich in fibers, carbohydrates, and proteins can accumulate lactobacillus. If the mother gets exposed to energy-dense foods, it can change the composition of immune cells in the breast milk. This can cause defects in the infants' immune system maturation. Similarly high intake of junk and snack foods by the breastfeeding mother can also negatively impact the infants' immune system.
Will Obesity in Breastfeeding Mothers Affect the Immunity of Infants?
Obesity in breastfeeding mothers also plays a role in the immunity of the infants. It can cause alteration in the neurodevelopment of newborns. Evidence suggests an association between maternal body mass index (BMI) and higher omega-6 to omega-3 fatty acid ratios as well as lower levels of lutein, docosahexaenoic, eicosapentaenoic, and docosapentaenoic acids in breast milk. It is also confirmed that maternal inflammation correlates favorably with breast milk contents of saturated and monounsaturated fatty acids.
Conclusion
Breastfeeding has a key role in the development of the immune system in newborns. The composition of breastmilk includes several immune cells such as natural killer cells, innate lymphoid cells, cytotoxic cells, T-regulatory cells, B cells, neutrophils, etc. Infants fed with formula milk have been found to have slower development of the immune system compared to infants fed with breast milk. Breastfeeding helps newborns develop physiological immunity, reducing their risk of infection and disrupting their microbiome as well as their immunological tolerance and inflammatory immune profile.
