Milk - It Does a Baby's Immune System Good

Written by: Tyler Quigley

show/hide words to know

Immune molecule: a molecule that is involved in preventing, fighting, or recovering from an illness.

Iron: an important nutrient that is used for various cellular processes, including the movement of oxygen in the body.

Lactoferrin: an immune molecule that is known to keep iron away from harmful bacteria, which need the iron to survive.

Secretory immunoglobulin A: (sIgA) an immune molecule found in mucus (like snot) that prevents harmful viruses, bacteria, and fungi from surviving inside the body.

What's in the Story?

mother breastfeeding baby

Humans are mammals, a group that is named for their mammary glands. In most female mammals, mammary glands can produce milk for young. Image by honey-bee.

If you ever have spent time in a public place, such as a mall or a park, you may have noticed a mother breastfeeding her baby. Why does she do that? Well, that mother has produced important nutrients inside her body, which she delivers to her baby through breast milk. Some parents choose to feed their babies formula, which is baby food that is supposed to provide the same healthy ingredients as breast milk. But scientists have shown that infants who are fed their mothers’ natural breast milk usually do not get sick as often as formula-fed babies. How exactly does breast milk help prevent disease in infants?
In the Evolution, Medicine, and Public Health article, “Illness in breastfeeding infants relates to concentration of lactoferrin and secretory Immunoglobulin A in mother’s milk,” scientists study the relationship between disease in infants and two important immune molecules.

Why Study Breast Milk?

Breast milk has been described as “liquid gold” because it provides just the right balance of nutrients that babies need. But breast milk also has additional beneficial molecules that help protect babies from illness. Besides having a lower chance of catching an illness, breastfed babies that do get sick tend to recover more quickly than babies who are not breastfed. 

In developing countries, where diseases are more prevalent, breastfeeding is especially important for keeping infants healthy. Thus, scientists are interested in learning exactly how breast milk is beneficial to infants, in a variety of different populations.

Breast Milk and Infant Immunity 

H'Mong girl

Lactoferrin and sIgA are found in mucus, which we are most familiar with from runny noses. Image by Bùi Linh Ngân from Hanoi, Vietnam.

Every mother’s breast milk has slightly different amounts of two immune molecules: lactoferrin and secretory Immunoglobulin A (sIgA). Lactoferrin hangs out in our body’s mucus, in places like our noses, throats, and on the outsides of our organs. It is really good at binding to iron, an act that helps keep the iron away from any bacteria that might need it to survive. It is also pretty good at helping other immune cells grow and function properly.

Secretory Immunoglobulin A also hangs out around our mucus, stopping bacteria and viruses from sticking to our organs. It can also collect a bunch of bacteria and viruses into a big ball, which helps the body process and get rid of the bacteria and viruses. 

The researchers believe these immune molecules in mothers’ breastmilk may be playing two different roles: 

1) In the protective role, the immune molecules are present in breast milk all of the time, so that illness can be prevented.

2) In the responsive role, the immune molecules are added to breast milk by the mothers’ body only in response to an illness in the infant.

The researchers hypothesized that any differences in the amount of lactoferrin and sIgA in breast milk would be associated with symptoms of illness in the infants. To test their idea, the researchers focused on the Qom/Toba people, a native population in Argentina. Many of the Qom people live in traditional conditions, such as in houses with dirt floors, and in communities with shared bathrooms, shared water sources, and outdoor cooking practices. Although the Qom have access to healthcare, their living conditions increase the chances of catching an illness relative to conditions in the United States or other more developed areas.

Connecting Breast Milk and Illness

Hindmilk breast milk

Milk varies in its nutrition and concentration of immune molecules over time. Image by Azoreg.

Thirty Qom mother-infant pairs participated in this study. Once a month for 4-5 months, the researchers visited each mother and her infant to collect data. At each visit, the researchers collected some of the mothers’ breast milk and asked them a few questions. The questions were mainly about the infants’ health over the previous month, and what symptoms of illness they might have shown. In addition, the researchers asked questions about infant health before the study, and then again a few months after the study ended. Collected milk was analyzed for lactoferrin and sIgA molecules. By putting data on each infant’s health together with the levels of immune compounds present in each sample of mother’s milk, the researchers could draw conclusions about how infant health and breast milk might be related.

Making Sense of Immunity in Milk

The researchers found that when lactoferrin was elevated in the breast milk, the infant was more likely to have been sick both before and after the milk sampling point. This suggests that lactoferrin may be playing a responsive role, which means the presence of the illness causes a rise in lactoferrin. On the other hand, the researchers found that high levels of sIgA in the mother’s breastmilk meant that their child was less likely to have been sick both before and after the study. This suggests that sIgA may have a protective role, which means that it may be present at all times to help prevent illness. 

Diagram of infant immune response

This diagram illustrates a theory of the relationship of sIgA and lactoferrin with infant illness. Click for more detail.

Taken together, both lactoferrin and sIgA represent the different roles that breast milk molecules can play in promoting infant health. While levels of sIgA seem to be elevated all of the time, lactoferrin seems to only be elevated after an infant is sick. If both molecules promote health, why doesn’t the mother’s body produce both compounds at all times? Well, one reason might be that it might cost a lot more energy to make lactoferrin than sIgA. If this is the case, it would make sense that the mother would only make lactoferrin when the infant needs it most.

So we see, one way a mother can invest in her baby is to give it the immune molecules it needs to protect itself from illness. But rather than providing high levels of those molecules all the time, it looks like there may be a balance between what the baby needs and what the mother gives. The results of this study tell us that the mother’s body is always adding some healthy molecules to her breast milk, but when her child is sick, she is able to give an extra boost of immunity to try to help her baby fight illness.

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Additional images via Wikimedia Commons. Painting of woman and child on menu thumnbnail by Alexey Venetsianov.

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Bibliographic details:

  • Article: Milk - It Does a Baby's Immune System Good
  • Author(s): Tyler Quigley
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: October 24, 2016
  • Date accessed: April 13, 2024
  • Link:

APA Style

Tyler Quigley. (2016, October 24). Milk - It Does a Baby's Immune System Good. ASU - Ask A Biologist. Retrieved April 13, 2024 from

American Psychological Association. For more info, see

Chicago Manual of Style

Tyler Quigley. "Milk - It Does a Baby's Immune System Good". ASU - Ask A Biologist. 24 October, 2016.

MLA 2017 Style

Tyler Quigley. "Milk - It Does a Baby's Immune System Good". ASU - Ask A Biologist. 24 Oct 2016. ASU - Ask A Biologist, Web. 13 Apr 2024.

Modern Language Association, 7th Ed. For more info, see
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