The Powerful Immunity in Breast Milk
The human system of immunity in breast milk. The immune system is a network of cells and proteins that defends the body against infection. If bacteria, a virus or other foreign substance enters the body, white blood cells identify it and produce antibodies and other responses to the infection. They also “remember” the attack so they can fight it more easily next time. A baby’s immune system is immature when they are born. It develops throughout life as they are exposed to different germs that can cause disease.
Infants’ Immune Systems
Although the mother’s placenta provides some antibodies, newborns enter the world largely unprotected. Antibodies are passed from mother to baby through the placenta during the third trimester (last 3 months of pregnancy). This gives the baby some protection when born.
These proteins 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. The type and amount of antibodies passed to the baby depends on the mother’s own level of immunity.
Their immune systems are undeveloped, which leaves them at risk for infections and serious illnesses. An infant produces antibodies efficiently by about six months of age, but their immune system is not fully developed until about age four or five.
This is one of the reasons why it is important to breastfeed your baby for as long as possible. Breastmilk protects against illness and encourages development of the immune system. Breastfeeding and vaccinating your baby will help protect them from a serious illness.
Breastmilk contains lymphocytes and macrophages that produce antibodies and other immune factors. It provides lactobacillus bifidus, the “friendly” bacterium that helps prevent the growth of dangerous bacteria. Other molecules in breastmilk actually kill harmful bacteria. In addition to providing protection against pathogenic bacteria, breastmilk contains elements that guard against viruses, fungi and parasites.
During birth, bacteria from the mother’s vagina is passed on to the baby. This helps to build the colony of bacteria in the gut that contributes to their immunity. After birth, more antibodies are passed on to the baby in colostrum and in breast milk.
Immunoglobulins and Premature Babies
A premature baby’s immune system is not as strong as the immune system of a full-term baby. They haven’t had as many antibodies passed to them from their mothers. Preemies are at a greater risk of getting an infection, and they have a harder time dealing with infections when compared to full-term infants. That’s why breast milk is so important for premature babies.
The antibodies in breast milk will help preemies fight off bacterial and viral infections. Babies produce their own antibodies every time they are exposed to a virus or germ, but it takes time for this immunity to fully develop. The passive immunity passed on from the mother at birth also doesn’t last long and will start to decrease in the first few weeks and months after birth.
Immunoglobulins and Day Care
Babies who need to go to daycare can benefit from breast milk. The antibodies breast milk can help protect them from many of the common childhood illnesses that can be easily picked up in a childcare setting. Breastfed babies are less likely to get gastrointestinal illnesses that cause diarrhea and vomiting. They also have a lower rate of respiratory infections and ear infections when compared to formula-fed children.
Boost your Baby’s Immune System
Each time your baby gets sick, they are developing new antibodies that will protect them in the future. In the meantime, there are some important things you can do to protect your baby.
Benefits for the Developing Immune System
The importance of breastfeeding in building a strong immune system. Breastmilk is much more than food. In addition to providing the absolute best nutrition for a growing body, breastmilk supplies the factors needed to develop the immune system that protects your baby from disease. Breastfeeding also adds the loving touch and comfort that is crucial to the growth and well-being of your baby.
Breast milk contains many elements that support your baby’s immune system. These include proteins, fats, sugars, antibodies, and probiotics. When a mother comes into contact with germs, she develops antibodies to help her fight off the infection. These are passed to the baby in breast milk. The baby is protected since mothers and babies are usually exposed to the same germs.
Breastfed babies have fewer infections and recover more quickly than formula-fed babies. However, breastfeeding cannot protect your baby from serious, life-threatening infections like polio, diphtheria or measles.
How Breast Milk Protects Newborns
Doctors have long known that infants who are breast-fed contract fewer infections than do those who are given formula. Until fairly recently, most physicians presumed that breast-fed children fared better simply because milk supplied directly from the breast is free of bacteria.
Formula, which must often be mixed with water and placed in bottles, can become contaminated easily. Yet even infants who receive sterilized formula suffer from more meningitis and infection of the gut, ear, respiratory, and urinary tracts than do breast-fed babies.
The reason, it turns out, is that mother’s milk actively helps newborns avoid disease in a variety of ways. Such assistance is particularly beneficial during the first few months of life, when an infant cannot produce an effective immune response.
Extra Protection
But breast-fed infants gain extra protection from antibodies, other proteins and immune cells in human milk. Once ingested, these molecules and cells help to prevent microorganisms from penetrating the body’s tissues. Some of the molecules bind to microbes in the hollow space (lumen) of the gastrointestinal tract.
In this way, they block microbes from attaching to and crossing through the mucosa—the layer of cells also known as the epithelium—that lines the digestive tract and other body cavities.
Other molecules lessen the supply of particular minerals and vitamins that harmful bacteria need to survive in the digestive tract. Certain immune cells in human milk are phagocytes that attack microbes directly. Another set produces chemicals that invigorate the infant’s own immune response.
Although it is not the norm in most industrial cultures, UNICEF and the World Health Organization both advise breast-feeding to “two years and beyond.” Indeed, a child’s immune response does not reach its full strength until around age five.
Immunoglobulins in Breast Milk
Immunoglobulins are antibodies. They’re proteins that are made by your immune system after exposure to an antigen (something harmful to your body that causes an immune response). Immunoglobulins fight off germs, illness, and disease. They circulate throughout the body and can be found in your blood, sweat, saliva, and even in breast milk.
Immunoglobulins take five basic forms, denoted as IgA, IgD, IgE, IgG, and IgM. All have been found in human breast milk, but by far the most abundant type is IgA. Specifically, the form known as secretory IgA, which is found throughout the gut and respiratory system of adults.
Secretory IgA in Breast Milk
Secretory Immunoglobulin A (IgA) is a special immunoglobulin. It’s the main antibody found in breast milk. IgA is considered the most important immunoglobulin in breast milk, and it’s also the one that’s talked about the most. These antibodies consist of two joined IgA molecules, and a secretory component. This component seems to shield the antibody molecules from being degraded by gastric acids and enzymes in the digestive tract.
IgA is important because it coats and seals your baby’s respiratory and intestinal tracts to prevent germs from entering his body and his bloodstream. The IgA antibodies can protect your child from a variety of illnesses including those caused by bacteria, viruses, fungi, and parasites.
Babies are born with low levels of IgA. Then, as the weeks and months go on, a baby’s immune system makes more IgA and the levels slowly rise. But, when a baby breastfeeds during this early period of life, he gets high levels of IgA from breast milk.
Infants who are bottle-fed have few means for battling ingested pathogens until they begin making secretory IgA on their own. Often several weeks, or even months after birth. The secretory IgA molecules passed to the suckling child are helpful in ways that go beyond their ability to bind to microorganisms and keep them away from the body’s tissues.
Other Immunoglobulins in Breast Milk
The other four: IgE, IgG, IgM, and IgD can be found in colostrum. Colostrum is the first breast milk to come in. It has very high levels of immunoglobulins, especially IgA. Not only do these immune factors fight off illness and infection, but they also protect against allergies (milk allergies, eczema, wheezing).
As your breast milk changes from colostrum to transitional milk, and finally to mature breast milk, the concentrations of immunoglobulins change. However, even after breastfeeding for a year or longer, these immune properties, including IgA, can still be found in breast milk.
They will continue to protect your baby for as long as you breastfeed him. In fact, your child will continue to benefit from the immunity in your breast milk long after breastfeeding has ended.
Primary Support
First, the collection of antibodies transmitted to an infant is highly targeted against pathogens in that child’s immediate surroundings. The mother synthesizes antibodies when she ingests, inhales, or otherwise comes into contact with any pathogen.
Each antibody she makes is specific to that agent; that is, it binds to a single protein (antigen), on the agent and will not waste time attacking irrelevant substances. Because the mother makes antibodies only to pathogens in her environment, the baby receives the protection it most needs in the first weeks of life.
Secondary Support
Second, the antibodies delivered to the infant ignore useful bacteria normally found in the gut. This flora serves to suppress the growth of harmful organisms, thus providing another measure of resistance. Secretory IgA molecules further keep an infant from harm in that, unlike most other antibodies, they ward off disease without causing inflammation—a process in which various chemicals destroy microbes but also hurt healthy tissue.
In an infant’s developing gut, the mucosal membrane is extremely delicate, and an excess of these chemicals can do considerable damage. In many countries, particularly in the Middle East, western South America and northern Africa, there is the tradition of mothers putting milk in their infants’ eyes to treat infections there.
An Abundance of Helpful Molecules
Several molecules in human milk besides secretory IgA prevent microbes from attaching to mucosal surfaces.
Oligosaccharides
Oligosaccharides, which are simple chains of sugars, often contain domains that resemble the binding sites through which bacteria gain entry into the cells lining the intestinal tract. Thus, these sugars can intercept bacteria, forming harmless complexes that the baby can then excrete.
Mucins
Human breast milk contains large molecules called mucins that consisting of protein and carbohydrates. They, too, are capable of adhering to bacteria and viruses to safely eliminate them from the body.
Lactoferrin
Each molecule of a protein called lactoferrin can bind to two atoms of iron. Because many pathogenic bacteria thrive on iron, lactoferrin halts their spread by making iron unavailable to them.
It is especially effective at stalling the proliferation of organisms that can cause serious illness, like Staphylococcus aureus. Lactoferrin also disrupts the process by which bacteria digest carbohydrates, further limiting their growth. Similarly to B12 binding protein, which deprives microorganisms of vitamin B12.
Other compounds in human milk stimulate a baby’s own production of secretory IgA, lactoferrin, and lysozyme. All three molecules are found in the urine of breast-fed babies. Which is probably why breast-fed infants have a lower risk of urinary tract infections.
Lactobacillus
Bifidus, one of the oldest known disease resistant factors in human breast milk, promotes the growth of a beneficial organism named Lactobacillus bifidus. Free fatty acids present in milk can damage the membranes of viruses, like the chicken pox virus. These are packets of genetic material encased in protein shells.
Interferon
Interferon, found particularly in colostrum, also has strong antiviral activity.
Fibronectin
Fibronectin, also present in colostrum, can make certain phagocytes more aggressive. Aggressive phagocytes will ingest microbes even when the microbes have not been tagged by an antibody. Like secretory IgA, fibronectin minimizes inflammation; it also aids in repairing tissue damaged by inflammation.
Cellular Defenses
Immune cells are abundant in human breast milk. They consist of white blood cells (leukocytes) that fight infection and activate other defense mechanisms. The largest amount is found in colostrum.
Most of the cells are neutrophils, a type of phagocyte that circulates in the bloodstream. Neutrophils continue to act as phagocytes in the infant’s gut, but are less aggressive than blood neutrophils. They virtually disappear from breast milk six weeks after birth.
The next most common milk leukocyte is the macrophage, which is phagocytic (like neutrophils), and performs a number of other protective functions. Macrophages make up some 40 percent of all the leukocytes in colostrum.
Macrophages are far more active and motile than milk neutrophils. Aside from being phagocytic, macrophages manufacture lysozyme, increasing its amount in the infant’s gastrointestinal tract. Lysozyme is an enzyme that destroys bacteria by disrupting their cell walls. In addition, macrophages in the digestive tract can rally lymphocytes into action against invaders.
Lymphocytes make up the remaining 10 percent of white cells in 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.
Milk lymphocytes behave differently from blood lymphocytes. Milk lymphocytes will proliferate in the presence of Escherichia coli, a bacterium that can be life-threatening for babies; but are less responsive than blood lymphocytes to agents that pose a lesser threat.
Milk lymphocytes manufacture several chemicals—including gamma-interferon, migration inhibition factor, and monocyte chemotactic factor—that can strengthen an infant’s own immune response.
Added Benefits
Some factors in human breast milk may induce an infant’s immune system to mature more quickly. Breast-fed babies produce higher levels of antibodies in response to immunizations.
Certain hormones in milk (cortisol) in combination with smaller proteins (epidermal growth factor, nerve growth factor, insulinlike growth factor, and somatomedin C) act to close up the mucosal lining in the newborn, making it impermeable to pathogens.
Animal studies have demonstrated that postnatal development of the intestine occurs faster in animals fed their mother’s milk. Animals that also receive colostrum, which contains the highest concentration of epidermal growth factor, mature even more rapidly.
Long Term Breastfeeding
Long-term breastfeeding and natural weaning (letting your child decide when to wean) is by far the healthiest way to build a healthy immune system. Continuing to breastfeed into the preschool years does not necessarily make a child dependent on the mother.
Breastfeeding and Lifelong Immunity
Breastfeeding can boost an infant’s immune system for life, according to a group of scientists that studied mice. According to the World Health Organization (WHO), exclusively breastfeeding a child until they are six months old can help brain development, avoid malnutrition, reduce infections, and lower the risk of obesity, sudden infant death syndrome, and childhood leukemia.
Breastfeeding can also boost the mother’s health; cutting her risk of breast and ovarian cancers, osteoporosis, obesity, and heart disease.
Breastfeeding When Mom or Baby are Sick
When mothers are exposed to a virus, they begin producing antibodies to fight the infection. Some of these antibodies are passed to their baby through breastmilk so he can also fight the same virus. When your baby is sick, it makes sense to nurse him even more frequently. In addition to providing antibodies, breast milk is a nourishing calorie-rich fluid, which keeps a baby well hydrated.
Pumping and Storing Breast Milk
When pumping, some of the bacteria and germs on your skin can get into the storage container, along with your breast milk. The immune factors in breast milk help to prevent this bacteria from growing. If you pump it’s important to follow the safety guidelines for the collection and storage of breast milk:
- Breast milk stored in the refrigerator maintains most if its immune properties.
- Freezing breast milk will lose some of its healthy immune factors.
- Heating breast milk at high temperatures (like in the microwave) will destroy the antibodies and other immune factors in breast milk.
When breast milk is collected and stored safely, even with the loss of some immune factors, it’s still better than any infant formula available.
Breastfed Babies and Vaccinations
While breast milk provides your baby with important immune protection, it does not protect your baby from all diseases. Many dangerous and deadly illnesses are preventable through childhood immunizations.
There are strong opinions on both sides of the vaccine debate. But every parent must learn all the facts about vaccines and discuss the issue with their child’s pediatrician. A pediatrician will provide you with a schedule of recommended vaccines for your child at each developmental stage.
Vaccination causes an immune response in the same way that a virus would. When the child comes into contact with the real disease in the future, their immune system will recognize the germ, and respond fast enough to fight off the disease.
Pregnant women are vaccinated for whooping cough in their third trimester so they will pass on that immunity to their babies. Babies have their first vaccinations at birth, then some more at 6 weeks, 4 months and 6 months, and for the first few years of life. Vaccinating children is still the safest and most effective way to protect them against serious disease.
Diet and Supplements
Taking antibiotics will kill healthy gut bacterium that are important for immunity. Probiotics are often suggested as a way of boosting babies’ immunity after they have had antibiotics.
Probiotics are safe to use in late pregnancy and after the baby is born. However, evidence regarding the benefits for children or adults is minimal. It is best to get probiotics and prebiotics from food. Always consult your baby’s pediatrician before giving probiotics to your baby.
In most cases, breast milk and formula provide all the vitamins and minerals your baby needs. Additional vitamin supplements are not recommended for babies. Once your baby starts on solids, a variety of fresh foods including different types of pureed vegetables and fruits should be enough to keep their immune system healthy. It is still best to keep breastfeeding while you’re introducing solid foods.
Sources:
How your baby’s immune system develops
https://www.pregnancybirthbaby.org.au/how-your-babys-immune-system-develops
Last reviewed: June 2019
How Breast Milk Protects Newborns
https://kellymom.com/pregnancy/bf-prep/how_breastmilk_protects_newborns/
Written by Jack Newman, MD, FRCPC, Jan 2, 2018
Breastfeeding for a Strong Immune System
https://www.healthychild.com/breastfeeding-for-a-strong-immune-system/
By Jane Sheppard CPC FMCHC
Immunoglobulins (Antibodies) In Breast Milk
https://www.verywellfamily.com/immunoglobulins-antibodies-in-breast-milk-431993
By Donna Murray, RN, BSN, Reviewed by Rebecca Agi, MS, IBCLC, on May 28, 2020
Kids Health from Nemours
Breastfeeding vs. formula feeding
https://kidshealth.org/en/parents/breast-bottle-feeding.html
Reviewed by: Elana Pearl Ben-Joseph, MD, Updated June 2018
Immunology of breast milk
https://doi.org/10.1590/1806-9282.62.06.584
by Palmeira P, Carneiro-sampaio M., Rev Assoc Med Bras. 2016;62(6):584-593. doi:10.1590/1806-9282.62.06.584
Centers for Disease Control and Prevention
Proper storage and preparation of breast milk
https://www.cdc.gov/breastfeeding/recommendations/handling_breastmilk.htm
Updated January 2020.
Academy of Nutrition and Dietetics
Keeping breast milk safe
https://www.eatright.org/homefoodsafety/safety-tips/food-poisoning/keeping-breast-milk-safe
Updated May 2017.
Keeping Your Child Healthy in a Germ-Filled World: A Guide for Parents
https://jhupbooks.press.jhu.edu/title/keeping-your-child-healthy-germ-filled-world
by Kourtis AP
Johns Hopkins University Press. 2011
Centers for Disease Control and Prevention
Immunizations and Developmental Milestones for Your Child from Birth Through 6 Years Old
https://www.cdc.gov/vaccines/parents/downloads/milestones-tracker.pdf
Breastfeeding Can Give Lifelong Immunity Against Infection
https://www.newsweek.com/breastfeeding-1437941
By Kashmira Gander, May 29, 2019
Australasian Society of Clinical Immunology and Allergy (Immune system)
https://www.allergy.org.au/
Australian Breastfeeding Association (Breastfeeding and Immunity)
https://www.breastfeeding.asn.au/
Australian Government Department of Health (How does immunisation work?)
https://www.health.gov.au/
Royal Children’s Hospital Melbourne (Probiotics for infants and children)
https://www.rch.org.au/
The Royal Society (Evolution of the immune system in humans from infancy to old age)
https://royalsocietypublishing.org/