Immunobiology of Human Milk:
How Breastfeeding Protects Babies
by Lars A. Hanson, MD, PhD
Pharmasoft Publishing, 2004
reviewed by Margaret Bickmore
Longmont CO USA
From: LEAVEN, Vol. 41 No. 4, August-September 2005, pp. 88-89.
Ask almost anyone about reasons to breastfeed, and "for the immunities" is a likely response. Most La Leche League Leaders have probably said this phrase numerous times. Yet, have you ever wondered exactly how this process works? How do the breasts know what antibodies and immune factors to send to the baby, and how do they do it?
The Immunobiology of Human Milk: How Breastfeeding Protects Babies by Lars Hanson, MD, PhD, explains the concepts in detail and is an important book for breastfeeding supporters.
Dr. Hanson has a long and distinguished career as a pediatrician and immunobiologist, has published over 650 scientific papers, and has edited or contributed to 19 books. He calls this book "his scientific testament" because it contains the condensed version of his life's work on human milk. It is packed with fascinating information about the role of breastfeeding and human milk in the development of the infant's immune system.
While The Immunobiology of Human Milk is directed at nonspecialists, it is not a book for the average lay reader. Those without a background in immunology are likely to find it challenging reading. Dr. Hanson has attempted to convey a complex and intricate subject as clearly as possible by highlighting key points in boxes throughout the text and by ending each chapter with a concise summary. However, this is a subject that resists simplification. I concur with the warning in the introduction: "After reading this book, you may agree with the saying, ‘Still confused, but at a higher level.'" The chapter and section titles listed in the table of contents were so intriguing, though, that they motivated me to persevere and read the entire book.
The early chapters are devoted to the subject of the "host defense." The individual's immune system and the specific immunological issues of pregnancy. This portion of the book is highly technical. Later chapters brim with fascinating information about components of human milk and specific ways that breastfeeding provides protection against disease.
In a section about the colonization of the intestinal systems in newborn babies, Dr. Hanson explains how human milk favors the growth of low-virulence bacteria, which then crowd out other potentially more dangerous strains of bacteria in the infant's intestinal system (commonly known as the "gut"). For example, the strains of E. coli in breastfed babies are likely to be less-infectious types than the E. coli in artificially fed babies. Hygienic procedures that are initiated by medical staff soon after birth may limit or delay the normal, beneficial bacterial colonization of the infant and actually increase the risk of infection by harmful bacteria. It is important for the infant's gut to be colonized with the right bacteria because "these microbes are the main stimulus for the growth of the immune system of the newborn." Human milk encourages the growth of "good" bacteria and hinders the presence of "bad" bacteria.
A typical immune response in a person with a well-functioning immune system involves local inflammation, fever, loss of appetite, and aches and pains. This kind of immune response is effective, but costly. It requires energy and causes discomfort and minor tissue damage. These costs are manageable for most people but may hinder the optimal growth and development of an infant. The immune factors in human milk have the remarkable feature of fighting infection without inducing inflammation. The immune factors in human milk intercept pathogens before they have a chance to cause infection, and they scale back the parts of the immune system that are pro-inflammatory. This is a great boon to breastfed babies! They resist many infections without ever feeling ill or directing any of their energy away from growth.
I was fascinated to learn just how the mother's body makes antibodies in her milk that are specific to her baby's needs. Peyer's patches are specialized areas in the mother's gut, which draw in material from the gut, including microbes and food. One type of white blood cells, lymphocytes, found in the patches respond with specific antibodies, then the lymphocytes themselves migrate to the breasts and other exocrine glands as well as mucous membranes. The antibodies are then produced in the mother's milk. This arrangement is called the entero-mammaric link, and it ensures that breastfed babies are protected against pathogens, which attack mucous membranes.
It is sometimes said that human milk, and particularly colostrum, "paints" or "coats" the baby's gut with protective factors. This is a description of the action of secretory immunoglobulin A (SIgA), which comprises 80 percent of the antibodies in human milk:
SIgA antibodies prevent microorganisms from entering tissues via the mucosal membranes. SIgA is produced in the gut in early life. If the child is heavily exposed [to microbes], this defense system develops more quickly. While the young infant is developing this defense system, it receives huge amounts of SIgA antibodies against microbes from the mother's surroundings via the maternal milk.
Because most infections in humans occur through the mucous membranes, SIgA protection is especially important.
The chapters "Mother's Defense of the Offspring via the Milk" and "Breastfeeding and Protection Against Disease" were interesting and seem to be the most relevant for those who are helping mothers breastfeed. Each of the immune components of milk is discussed in detail. Dr. Hanson explains breastfeeding's protective role against various illnesses. One of the longer sections is devoted to breastfeeding and allergy. Research results have sometimes been conflicting as to whether breastfeeding is protective against different kinds of allergic disease or not. Dr. Hanson notes that the fatty acid composition of the mother's diet, specifically the ratio of omega-6 to omega-3 fats, may be an important factor and may account for some of the puzzling results. Mothers who consume more "good" omega-3 fats may have babies who are better able to tolerate potential allergens without generating an inappropriate immune response.
A final chapter addresses infectious agents in human milk, including HIV. Dr. Hanson's view is that human milk may contain factors that actively fight against HIV, and that exclusive breastfeeding may be protective. However, he states, "Formula-feeding is safe in developed areas with clean water and informed mothers." This is the only part of the book that disappointed me. Considering Dr. Hanson's unparalleled understanding of the immunobiology of human milk, I hoped for a stronger statement from him in regard to HIV and breastfeeding rather than the very conservative and cautious position he takes.
Scientifically inclined breastfeeding advocates may find this book a sometimes challenging but useful guide with its evidence-based discussions and exhaustive references. I am happy to have it on my bookshelf and feel that it will be a helpful LLL Professional Liaison Department resource. Lactation consultants, physicians, and other interested health care professionals will find this book informative.
Margaret Bickmore lives in Longmont, Colorado, USA with her husband, Clint, and three sons, Cade (7), Torin (3), and Rand (7 months). She is an active Leader with LLL of Longmont and also serves as Area Professional Liaison for Colorado/Wyoming. Christine McNeil Montano is the Leaven Book Review Editor. She has been a Leader since 1999 and is a member of the LLLI Book Evaluation Committee. She and her husband, Tony, have two children: Jay (7) and John (5). Send your ideas to Christine at cmmontano at snet dot net.