The Importance of Breast Feeding to a Baby’s Health


By Richard Kieninger


Doctors have long known that infants who are breastfed contract fewer infections than those who are given formula.  Formula, which must often be mixed with water and placed in bottles, can easily become contaminated, and indeed, infants who receive sterilized formula suffer higher rates of meningitis and infections of the gut, ear, respiratory tract and urinary tract than their breastfed counterparts.


Mother’s milk actively assists the child’s immune system for the first five years or so. During pregnancy, the mother passes antibodies (IgA, IgD, IgE, IgG, and IgM) to her fetus through the placenta. The antibodies circulate in the infant’s blood for weeks to months after birth, neutralizing microbes or marking them for destruction by phagocytes (immune cells that consume and break down bacteria, viruses and cellular debris).


Other molecules (oligosaccharides) and cells help to prevent microorganisms from penetrating the body’s tissues. Some of them bind to microbes in the hollow space (lumen) of the gastrointestinal tract thus blocking microbes from attaching to and crossing through the epithelium (the layer of cells that lines the digestive tract and other body cavities). Other molecules (lactoferrin) reduce the concentration of particular vitamins and minerals needed by harmful bacteria in the digestive tract. Other immune cells in human milk are phagocytes that attack microbes directly. Another set (gamma-interferon) produces chemicals that invigorate the infant’s own immune response.


The Antibodies

The most important antibody in human milk is called IgA. It is also found in great amounts throughout the gut and respiratory system of adults. This antibody shields other necessary molecules from being degraded by the gastric acid and digestive enzymes in the stomach and intestines. Infants who are bottle-fed are at risk against ingested pathogens until they begin making IgA on their own, which usually requires several weeks or months after birth.


The collection of antibodies contained in human milk is specially designed by the mother’s body to attack pathogens in that child’s immediate surroundings. The mother synthesizes these antibodies when she ingests, inhales or otherwise comes in contact with a disease-causing agent. Each antibody she makes is specific to that agent—binds to a single protein, or antigen, on the agent and will not attack other substances. Because the mother makes antibodies only to pathogens in her environment, the baby receives the protection it needs most against the infectious agents most encountered.


Furthermore, the antibodies delivered to the infant ignore useful bacteria normally found in the gut. These bacteria serve to crowd out the growth of harmful organisms, thus providing another measure of resistance.


The IgA molecules have a unique characteristic in that they ward off disease without causing inflammation-a negative side-effect of laboratory-made chemicals. In an infant’s developing gut, the epithelial membrane is extremely delicate, and an excess of these chemicals can do considerable damage. IgA also protects other similar membranes in the body.


Health-Enabling Molecules

Other molecules in human milk prevent microbes from attaching to the epithelial membranes. Oligosaccharides, which are simple chains of sugars, have a structure that resembles the binding sites through which bacteria gain entry into the cells lining the intestinal tract. This structure allows these sugar-like molecules to intercept bacteria, forming harmless complexes that the baby excretes. In addition, human milk contains large molecules called mucins that include a great deal of protein and carbohydrate. They also adhere to bacteria and viruses and then are harmlessly eliminated from the body.

The protein molecule lactoferrin binds to two atoms of iron, making them unavailable to the pathogenic bacteria that thrive on iron. It is especially effective against Staphylococcus aureus. Lactoferrin also disrupts the process by which bacteria digest carbohydrates, further limiting their growth Similarly, the binding of protein B12 deprives microorganisms of vitamin B12.


Bifidus factor, one of the oldest known disease-resistance factors in human milk, promotes the growth of a beneficial organism named Lactobacillus bifidus. Free fatty acids present in human milk can damage the membranes of enveloped viruses, such as the chicken pox virus, which are packets of genetic material encased in protein shells.


Interferon, present in colostrum—the scant, sometimes yellowish milk a mother produces during the first few days after birth—also has strong antiviral activity. Fibronectin, present in large quantities in colostrum, can make certain phagocytes more aggressive so that they will ingest microbes even when the microbes have not been tagged by an antibody. Like IgA, fibronectin minimizes inflammation and aids in repairing tissue that is otherwise damaged by inflammation.


Activities of Immune Cells

Immune cells are abundant in human milk. They consist of white blood cells and leukocytes that fight infection and activate defense mechanisms. The highest concentration is found in colostrum. Another type is called neutrophils. This immune cell type is less aggressive than blood neutrophils and virtually disappears from breast milk six weeks after birth and has the function of protecting the breast from infection.


The next most common milk leukocyte is the macrophage. Macrophages make up some 40 percent of all the leukocytes in colostrum. Aside from being phagocytic, the macrophages in breast milk manufacture lysozyme (an enzyme that destroys bacteria by disrupting their cell walls) increasing its amount in the infant’s gastrointestinal tract In addition, macrophages in the digestive tract can activate lymphocytes into action against invaders.


Lymphocytes constitute the remaining 10 percent of white cells in the milk. About 20 percent of these cells are B lymphocytes, which give rise to antibodies; the rest are T lymphocytes, which kill infected cells directly or send out chemical messages that mobilize other components of the immune system. Milk lymphocytes behave differently from blood lymphocytes. Those in milk, for example, proliferate in the presence of Escherichta coli, a bacterium that can cause life-threatening illness in babies, but they are far less responsive than blood lymphocytes to invaders posing less threat to infants. Milk lymphocytes also manufacture several chemicals-including gamma-interferon, a migration inhibition factor and monocyte chemotactic factor-that strengthens an infant’s own immune response.


Maturation of the Infant’s Immune System

Several studies indicate that some factors in human milk induce an infant’s immune system to mature more quickly than it would were the child fed artificially.


Certain hormones in milk (cortical) and smaller proteins (including epidermal growth factor, nerve growth factor, insulin-like growth factor and somatomedin C) act to close up the leaky mucosal lining of the newborn, making it relatively impermeable to unwanted pathogens and other potentially harmful agents.


Other compounds in human milk stimulate a baby’s own production of IgA, lactoferrin and lysozyme. These three molecules are found in larger amounts in the urine of breastfed babies than in that of bottlefed babies. These molecules are triggered into production in the mucosa of the infant’s urinary tract by breastfeeding.


Recent clinical studies have demonstrated that the breast-fed infant has a lower risk of acquiring urinary tract infections. The studies have also shown that an unknown factor in human milk causes breast-fed infants to produce more fibronectin on their own than do bottle-fed babies.


By protecting infants against infection until their bodies can protect themselves, breast milk supplies far more than just nutrition.