Breastmilk Benefits: Breastfeeding & Your Baby's Immune System

In part 1 of this series, we discussed all the vital nutrients present in breastmilk, highlighting their dynamic nature influenced by factors such as your baby’s age, feeding, and time of the day.

In this second part, we’ll explore further to uncover some of the remarkable bioactive compounds that breastmilk contains. These play a pivotal role in fortifying your baby’s immune system, shielding them from illnesses, and reducing the risk of chronic health conditions. And did you know that breastfeeding brings benefits for mom too? Keep reading to discover this connection between breastmilk and the immune system and its role in protecting both mother and baby.

The benefits of breastmilk for baby

Breastmilk contains bioactive compounds that support the immune system and development

Not only does breastmilk contain nutrients for your baby, but also bioactive compounds with anti-inflammatory effects that provide significant protection against infection [1]. These compounds help babies: 

• Develop their immune system
• Establish a healthy gut microbiome
• Reduce inflammation
• Fight diseases 

Some examples of bioactive compounds in breastmilk are [1]:

• Immunoglobulins, white blood cells, and antimicrobial peptides. These act like a ready-made immune system that protects your baby in the short term.
• Stem cells, cytokines, and beneficial bacteria. These help your baby’s immune system develop over the long term.
• Proteins like haptocorrin and lactoferrin. These help your baby to digest and absorb nutrients like iron and vitamin B12 [2].
• Growth factors and hormones. These bioactives promote gut maturation.
• Chemokines, growth factors, and microRNA. These send signals that tell genes when and how to express themselves.
• Human Milk Oligosaccharides (HMOS). These are a type of carbohydrate that feed your baby’s gut microbiome. 

One specific bioactive compound that helps immune system development are antibodies. These help fight illness, bacteria, viruses, and any unfriendly microbes in the human body. 

Passive immunity from antibodies in breastmilk builds your baby’s immune system

When the body is exposed to unfriendly microbes, the immune system develops antibodies to help fight them. Many antibodies can remain in the human body for a lifetime. This means that when mom gets exposed to the same unfriendly microbes, she will have an army of antibodies to immediately fight them.

Breastmilk contains several antibodies that mom passes to her baby to help fight unfriendly microbes. This is called passive immunity.

Passive immunity helps build your baby’s immune defenses against unfriendly microbes while their own immune system is still developing.

Even while sick with a common cold, breastfeeding is still recommended [3]. This is because it may pass antibodies– boosting your baby’s immunity. This also includes mastitis, which is inflammation of the breast ducts. Evidence suggests that moms with mastitis may continue breastfeeding and there is no risk to your baby [4], [5]. In fact, breastfeeding may even help alleviate mastitis. However, it’s also best to check with your provider to ensure that you may continue breastfeeding with certain illnesses.

If you are taking antibiotics or other medications, check with your provider if you can still provide breastmilk. 

Certain medications can be passed through breastmilk and be disruptive to your baby, although many are completely safe. You can check out the LactMed® database for potential medications and chemicals that can be passed to your baby through breastmilk.

Another way to develop antibodies is through vaccines. Vaccines help the human immune system develop antibodies for specific unfriendly microbes, without actually encountering them. This means that if you do ever encounter that specific unfriendly microbe, you will have an army of antibodies.

So if mom is vaccinated, the antibodies produced can potentially be transferred to her baby.

In fact, a recent study showed that breastmilk from both moms with COVID-19 infection and moms who received COVID-19 vaccination contained active antibodies necessary to neutralize the virus [6]. 

One specific antibody has been shown to play an essential role in immune function in babies: immunoglobulin A (IgA). IgA represents over 90% of breastmilk antibodies [7]. 

IgA has even been shown to modify bacterial gut colonization in newborns [8]. One of the main jobs of IgA is to stop unfriendly bacteria from inhabiting your baby’s gut by flagging their presence. This lets your baby’s immune system fight illnesses. 

Though in the early days, your baby doesn’t produce their own IgA. IgA has been shown to be passed from mom to baby through breastmilk. Colostrum, the earliest of breastmilk, provides high amounts of IgA, as well as several other antibodies [8]. This begins to build a strong immune system for your baby. 

Bioactive compounds changes in breastmilk 

Not only does the nutritional profile of breastmilk change, but the levels of bioactive compounds found in breastmilk are also in flux. 

The levels of antibodies are shown to be dynamic. The levels of IgA in breastmilk are the highest in colostrum and gradually decrease from transitional milk to mature milk [9].

Still, IgA levels in breastmilk remain high even after the second year of nursing [7]. This means that one of the benefits of extended breastfeeding, even after introducing solids, may be to provide antibodies to your baby. 

Assuming solid foods are introduced around 6 months, the World Health Organization currently supports breastfeeding for up to 2 years or beyond, and the American Academy of Pediatrics recommends 1 year or longer.

You may want to consider providing breastmilk for as long as possible, in addition to solids starting at around 6 months of age. Breastmilk provides the nutrition necessary for your baby to thrive but also helps build a strong immune system. 

Breastmilk decreases disease risk

Apart from providing the required nutrients for your baby, breastmilk has also been shown to reduce the risk of certain diseases. This is because breastmilk helps build a strong immune system and metabolism in your baby in their early life.

Compared to formula-fed babies, breastfed babies are less likely to develop health issues like pneumonia, diarrhea, and different infections [10]. 

Specifically, breastfeeding has been shown to decrease the risk of:

• Sudden infant death syndrome (SIDS) [11] 
• Childhood acute leukemia [12] 
• Crohn’s disease and ulcerative colitis [13] 
• Ear, throat, and sinus infections  [14]
• Diabetes [15]
• Allergic diseases [16]
• Respiratory infections [17] 
• Gastrointestinal infections [17] 
• Asthma [18]
• Obesity [19]

In addition to bioactive compounds that support your baby’s immune system, breastmilk can influence early metabolism. Babies that are exclusively breastfed for four months have a specific growth pattern and metabolism, compared to formula-fed babies. It is thought that there is a critical window early in life where proper nutrition may have major effects later in life [20]. This can lead to “thrifty phenotypes” to help improve chances of survival. When food resources are insufficient, it may trigger fast insulin release and an enhanced capacity to store fat– leading to poor health outcomes as an adult.

In other words, early nutrition may alter an infant’s chance of metabolic issues [20]. For example, breastfeeding for longer periods is shown to decrease the risk of a child becoming overweight or obese by 26% [19].

The benefits of breastfeeding for mom 

Why is breastfeeding important for moms? Not only does breastmilk reduce disease risk for your baby, but it also helps reduce disease risk for mom. 

The mother’s immune system while breastfeeding

Breastfeeding has been shown to decrease the risk of certain diseases, such as:

• Ovarian cancer [21] 
• Type 2 diabetes [22] 
• Cardiovascular disease [23] 
• Breast cancer [19]

This may have something to do with the hormonal changes that take place during breastfeeding. 

While nursing, the levels of estrogen decrease while the levels of prolactin, a hormone that helps with breastmilk production, increase. These increased levels of prolactin block the production of estrogen [24]. As a result, many mothers will not have a menstrual cycle, also known as amenorrhea. 

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But this delay in the menstrual cycle is beneficial. It decreases the exposure of estrogen over a lifetime. Having increased sex hormones, such as estrogen, has been linked with several cancers [24]. For every 12 months of breastfeeding, research shows that a woman's risk for breast cancer decreases by 4.3% [25]. Even more so, breastfeeding also decreases the risk of ovarian cancer by 24% [21]. 

Besides this link between breastfeeding and the immune system, there are also psychological benefits for mom. Breastfeeding helps to reduce the risk of postpartum depression, with effects maintained over the first 4 months postpartum [26].

A final word on breastfeeding

The evidence is clear that breastfeeding has multiple benefits both for mom and baby [19], [21]–[23], [26]. But unfortunately, many women struggle to breastfeed: In the US, only about 45% of moms exclusively breastfed their baby at 3 months old [27]. 

Two of the main reasons for cessation of breastfeeding are difficulties such as poor latching technique and difficulties expressing breastmilk [28]. Lack of paid family and medical leave, along with insufficient support from family and/or workplace, can also lead a mom to discontinue breastfeeding.

Some  free resources worth looking into:

• La Leche League USA: Free meetings, online education, and community support for the breastfeeding journey. Outside of the US? Find a support group near you.
• Baby Café USA: Free, drop-in, informal breastfeeding support groups that offer professional lactation care and intervention [29].

Paid resources:

• SimpliFed: Virtual breast and baby feeding support from prenatal to postpartum, covered by most health plans.
• Milkology: Online breastfeeding classes.
• Tinyhood: On-demand breastfeeding classes, from prenatal prep to pumping.
• Tiny+ Targeted: Our Fertility, Pregnancy, & Postpartum program gives you two microbiome tests and four coaching sessions with a microbiome specialist.

And if for any reason you’re not able to breastfeed, don’t stress. Infant formulas are improving and are starting to include more bioactive ingredients such as HMOs. You’ve got this, mom!