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Immunology – breastfeeding confers immuno-protective factors to the baby and helps build the baby’s immune system.

Updated March 22, 2022

Breastfeeding is now more important than ever as optimal nutrition for the child on the one hand, and on the other hand because of its important role for the human immune system.

Covid-19, breastfeeding, mother’s milk and the immune system

  • Didikoglu A et al. Early life factors and COVID-19 infection in England: A prospective analysis of UK Biobank participants (Feb 2021) https://doi.org/10.1016/j.earlhumdev.2021.105326 “The odds of contracting COVID-19 were 12% lower among respondents who were breastfed when they were babies.”
  • Pace et al COVID-19 and human milk: SARS-CoV-2, antibodies, and neutralizing capacity in Milk produced by women with Covid-19 (2020, Oct 21)https://journals.asm.org/doi/10.1128/mBio.03192-20#
  • Tong et al, Mother’s Milk May Inhibit COVID-19 (2020, Sept 29) https://www.medscape.com/viewarticle/938228?nlid=137631_2046&src=WNL_mdplsnews_201002_mscpedit_peds&uac=104320SJ&spon=9&impID=2599391&faf=1 Mother’s milk could help treat or prevent the coronavirus.
  • Van Keulen et al, Breastmilk; a source of SARS-CoV-2 specific IgA antibodieshttps://www.medrxiv.org/content/10.1101/2020.08.18.20176743v1 The research so far seems to back this up. Scientists at Amsterdam University say they have found multiple lines of evidence on the presence of a variety of antibodies that are effective against SARS-CoV-2 in the breastmilk of corona-affected women, with no such antibodies present in the controls.
  • Groß R, Conzelmann C, Müller JA, Stenger S, Steinhart K, Kirchhoff F, Münch J. 2020. Detection of SARS-CoV-2 in human breastmilk. Lancet 395:1757–1758.
  • Buonsenso D, Costa S, Sanguinetti M, Cattani P, Posteraro B, Marchetti S, Carducci B, Lanzone A, Tamburrini E, Vento G, Valentini P. 2020. Neonatal late onset infection with severe acute respiratory syndrome coronavirus 2. Am J Perinatol 37:869–872.
  • Kirtsman M, Diambomba Y, Poutanen SM, Malinowski AK, Vlachodimitropoulou E, Parks WT, Erdman L, Morris SK, Shah PS. 2020. Probable congenital SARS-CoV-2 infection in a neonate born to a woman with active SARS-CoV-2 infection. CMAJ 192:E647–E650.
  • Tam PCK, Ly KM, Kernich ML, Spurrier N, Lawrence D, Gordon DL, Tucker EC. 2020. Detectable severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in human breast milk of a mildly symptomatic patient with coronavirus disease 2019 (COVID-19). Clin Infect Dis doi: https://academic.oup.com/cid/article/72/1/128/5848850
  • Chen H, Guo J, Wang C, Luo F, Yu X, Zhang W, Li J, Zhao D, Xu D, Gong Q, Liao J, Yang H, Hou W, Zhang Y. 2020. Clinical characteristics and intrauterine vertical transmission potential of COVID-19 infection in nine pregnant women: a retrospective review of medical records. Lancet 395:809–815.
  • Fan C, Lei D, Fang C, Li C, Wang M, Liu Y, Bao Y, Sun Y, Huang J, Guo Y, Yu Y, Wang S. 2020. Perinatal transmission of COVID-19 associated SARS-CoV-2: should we worry? Clin Infect Dis https://pubmed.ncbi.nlm.nih.gov/32182347/
  • Lackey KA, Pace RM, Williams JE, Bode L, Donovan SM, Järvinen KM, Seppo AE, Raiten DJ, Meehan CL, McGuire MA, McGuire MK. 2020. SARS‐CoV‐2 and human milk: what is the evidence? Matern Child Nutr 16:e13032. https://pubmed.ncbi.nlm.nih.gov/32472745/
  • Dong Y, Chi X, Hai H, Sun L, Zhang M, Xie W-F, Chen W. 2020. Antibodies in the breast milk of a maternal woman with COVID-19. Emerg Microbes Infect 9:1467–1469. https://pubmed.ncbi.nlm.nih.gov/32552365/
  • Fox A, Marino J, Amanat F, Krammer F, Hahn-Holbrook J, Zolla-Pazner S, Powell RL. 2020. Robust and specific secretory IgA against SARS-CoV-2 detected in human milk. iScience 23:101735. https://pubmed.ncbi.nlm.nih.gov/33134887/
  • Chambers C, Krogstad P, Bertrand K, Contreras D, Tobin NH, Bode L, Aldrovandi G. 2020. Evaluation for SARS-CoV-2 in breast milk from 18 infected women. JAMA 324:1347–1348.

What do parents know?

Most parents know about the health impact of breastfeeding on babies but nothing about the immature immune system and how breastfeeding helps it strengthen and mature.

Breastfeeding not only strengthens the child’s immune system, but breast milk also contributes to the child’s development. Breastfeeding provides the child with many immuno-protective factors: specific (adapted to the mother’s and child’s environment) and non-specific (those present in the basic composition of breast milk from the beginning, such as IgA, cytokines, human oligosaccharides (about 200), tumour-killing proteins, and many others – the list is long (see below).

Moreover, breastfeeding builds and nourishes the child’s microbiota. Breast milk acts on the intestinal flora and mucous membranes, two important protective filters against pathogens and viruses. As researcher Lars A. Hanson wrote as early as 2004: Breastfeeding protects the baby, and in addition, it nourishes him. “Major components of human milk are not primarily for nutrition, but for host defense” (in Immunobiology of Human Milk – How Breastfeeding protects babies, 2004) .

Photograph of a bus poster in Luxemburg : To immunise my baby, I am breastfeeding


During the first two years of life, the thymus gland of the breastfed child is exceptionally large. It is the “organ” that produces T-lymphocytes or “killer” lymphocytes of infected cells and therefore plays an important role in the fight against immune aggression. In the non-breastfed child, the thymus is only half the size.


The protein-lipid complex HAMLET (human alpha-lactalbumin made lethal to tumor cells) has a broad spectrum of activity against cancer cells of different origin. (Ho et al. 2017)

List of immuno-protective factors transmitted to the infant via breastfeeding

alpha-Lactalbumin (variant)
alpha2-macroglobulin (like)
Bifidobacterium bifidum
CCL28 (CC-chemokine)
Chondroitin sulphate (-like)
Complement C1-C9
Free secretory component
Fucosylated oligosaccharides
Gangliosides GM1-3, GD1a, GT1b, GQ1b
Glycolipid Gb3, Gb
Glycoproteins (mannosylated)
Glycoproteins (receptor-like)
Glycoproteins (sialic acid-containing or terminal galactose)
Haemagglutinin inhibitors
Lactadherin (mucin-associated glycoprotein)
Lactoperoxidase       Lewis antigens
Milk cells (macrophages, neutrophils, B & T lymphocytes)
Mucin (muc-1; milk fat globulin membrane)
Nonimmunoglobulin macromolecules (milk fat, proteins)
Oligosaccharides (about 200 human oligosaccharides are known today)
(Tri to penta) phosphorylated beta-casein
Prostaglandins E1, E2, F2 alpha
RANTES (CC-chemokine)
Secretory IgA
Secretory leukocyte protease inhibitor (antileukocyte protease; SLPI)
Sialic acid-glycoproteins
sialylated oligosaccharides
Sialyloligosaccharides on sIgA(Fc)
Soluble bacterial pattern recognition receptor CD14
Soluble intracellular adhesion molecule 1 (ICAM-1)
Soluble vascular cell adhesion molecule 1 (VCAM-1)
Sulphatide (sulphogalactosylceramide)
Trypsin inhibitor
Vitamin A
vitamin B12
Xanthine oxidase (with added hypoxanthine)

What’s in Breastmilk – Poster

Difference between breastfeeding and feeding with human milk

The list of immunocompetent factors transmitted from mother to child through breastfeeding is not only considerable in itself but reveals part of the way in which breastfeeding functions: it is not a static assembly of ingredients, but a biological liquid resulting from its continuous and dynamic production during breastfeeding and mother-child skin-to-skin contact.

In other words, the fine-tuned adaptation of breast milk is the result of an ongoing dialogue between the mother’s microbial environment and that of her child. Thus, in addition to the many non-specific immunological factors transmitted to the infant, the mother provides targeted anti-infective agents and immunological factors for her child.

There is a significant difference between

  • breastfeeding with skin to skin contact and transfer of the mother’s antibodies and the anti-infective agents in the live cells to her child, and
  • the feeding with human milk using expressed (and transformed) breastmilk and delivered through feeding apparatus. 

That said, breast milk in any form (raw human milk, pasteurized human milk, individual donor milk or pooled breast milk…) will always be superior to “formula” or artificial baby milk which is always at risk for contamination: on the production site (check out here) and through preparation (follow WHO Guidelines for the safe preparation, storage and handling of powdered infant formula)

Breastfeeding and epigenetic information

Breastfeeding also provides epigenetic information to the child in the form of maternal stem cells, hormones and miRNA messengers which play an important role in metabolism and protection against non-communicable diseases (NCDs), known as “diseases of civilisation” (obesity, diabetes, cancer, hypertension, cardiovascular diseases…). Lancet Breastfeeding Series 2016

In a research study of 2017, Melnik & Schmitz describe it as follows: “There is accumulating evidence that milk functions as a transmitter or relay between the maternal lactation genome and epigenetic regulation of genes of the milk recipient, who under physiological conditions is the newborn infant […] Because human milk protects against diseases of civilization in later life, the World Health Organization recommends exclusive breastfeeding for up to six months with continuation of breastfeeding for at least the first two years.”

Milk’s Role as an Epigenetic Regulator in Health and Disease, Bodo C. Melnik and Gerd Schmitz, 2017 https://www.ncbi.nlm.nih.gov/pubmed/28933365