The newborn immune system is naïve to the dangers of the world. It can’t tell friendly bacteria from deadly ones, and it doesn’t yet know how to process food or eliminate environmental toxins. In the hours and days following birth, the newly-arrived gut bacteria provide the infant with an immunology crash-course: they teach the fledgling immune system how to attack pathogenic microorganisms and to tolerate their own presence—to differentiate microbial friend from foe, in other words. The ultimate goal of this learning process is oral tolerance—the ability to efficiently process the steady stream of microbes, food particles, and environmental toxins entering the body via the mouth.
Probiotic bacteria have a built-in advantage when it comes to colonizing the newborn intestine: long before they arrive on the scene, the gut is expecting them. The cells of the fetal gut and immune system contain toll-like receptors, proteins that recognize the newly arriving probiotic bacteria as birth progresses. Through a complex chain of chemical signals, the TLRs alert the immune system to welcome these “good” bacteria as they arrive, calming the kind of inflammatory reaction that unfamiliar bacteria would trigger. In this way, the immune system learns to tolerate health-promoting bacteria while retaining the ability to attack pathogenic invaders.
In a cesarean birth the fledgling immune system is confronted with unfamiliar, often hostile bacteria—humans did not co-evolve with Clostridium difficile, for example, a particularly troublesome hospital-acquired bug. In addition, the healthy probiotic bacteria associated with vaginal birth (e.g., lactobacillus) arrive later following a cesarean and have difficulty establishing themselves. These changes in the composition of the normal gut microbiota occur during a critical time in immune system development, and can lead to a world of health trouble. How?
The microbial battles in the gut are fought at the intestinal lining, the few-cells-thick mucosal surface that separates the bloodstream and the rest of the body from the waste products passing through the intestine. A healthy gut requires a network of tight junctions between the cells of the intestinal lining, junctions that physically and chemically make it difficult for unwanted microbes, toxins, or food particles to break through and cause illness.
When the composition of the microbiota is imbalanced, or unusual germs like C. difficile appear, the developing immune system can go a bit haywire. A long-lasting, low-grade inflammatory response directed at these unexpected intruders can begin at birth, weakening the tight junctions between cells and causing “leakiness” of the intestinal lining. This enables microbes and toxins that would normally be eliminated in the stools to make their way into the infant’s bloodstream.
To make a very long story short, that chronic inflammation and abnormal processing of microbial invaders, food particles, and environmental toxins that results, appear to increase the risk of asthma and eczema—and diabetes, obesity, and other chronic inflammatory and autoimmune conditions—later in life. Although the increase in risk may be small for a given baby, when extrapolated to the nearly 4 million annual births in the U.S., that’s a lot of potential disease.
A caveat: it’s good to remember that association does not prove causation. The fact that two things happen at the same time doesn’t necessarily mean that one is causing the other. As yet there is no “smoking gun” that proves cesarean birth is in part responsible for the increase in asthma and other chronic illnesses in recent decades. But as more and more research studies find increased risks of chronic disease in cesarean babies compared with those born vaginally, the cesarean-chronic illness link become stronger and harder to deny.
Conclusion
A cesarean section doesn’t automatically condemn a child to a lifetime of asthma or eczema, just as a vaginal birth isn’t a guarantee of perfect health. But cesarean birth, by altering normal gut microbiota and immune system development, does appear to moderately increase the risk of these and other chronic health conditions. This knowledge should serve as a strong argument against non-medically-indicated cesarean section.
About the Author: Mark Sloan M.D. is a pediatrician, writer, and medical educator living in Santa Rosa, California. His book, Birth Day: A Pediatrician Explores the Science, the History, and the Wonder of Childbirth, has been praised by the Washington Post, the New England Journal of Medicine, and the Journal of Midwifery and Women’s Health, and was named a 2010 Northern California Book Awards finalist. Published as Baby Science in Japan, Birth Day was named a ‘Top Ten Science Book of 2010’ by the Japan Economic Times. To read more about Mark Sloan: Mark Sloan M.D. or Dr. Sloan’s Blog.
Selected References
Effects of mode of delivery on gut microbiota composition:
- Biasucci G, Rubini M, Riboni S, et al (2010). Mode of delivery affects the bacterial community in the newborn gut. Early Human Development 86:S13-S15
- Penders J, Thijs C, Vink C, et al (2006). Factors influencing the composition of the intestinal microbiota in early infancy. Pediatrics 118(2):511-521.
- Salimen S, Gibson GR, McCartney AL (2004). Influence of mode of delivery on gut microbiota in seven year old children. Gut 53:1388-1389.
Development of the newborn immune system:
- Huurre A, et al (2008). Mode of delivery: Effects on gut microbiota and humoral immunity. Neonatology 93:236-240.
- Johnson C, Versalovic J (2012). The human microbiome and its potential importance to pediatrics. Pediatrics (published online April 2, 2012; DOI: 10.1542/peds2011-2736).
- Vael C, Desager, K (2009). The importance of the development of the intestinal microbiota in infancy. Current Opinion in Pediatrics 21(6):794-800
- Walker WA. Initial colonization in the human infant and immune homeostasis. Ann Nutr Metab 2013; 63 (suppl 2): 8-15.
Cesarean birth, gut microbiota, and asthma/atopic disease:
- Azad M, Korzyrkyj A (2012). Perinatal programming of asthma: The role of the gut microbiota. Clinical and Developmental Immunology Volume 2012; Article ID 932072; doi:10.1155/2012/932072
- Thanvagnanam S, Fleming J, Bromley A, et al (2008). A meta-analysis of the association between caesarean section and childhood asthma. Clinical & Experimental Allergy 38(4): 629-633.
- van Nimwegen F, Penders J, Stobberingh E, et al (2011). Mode and place of delivery, gastrointestinal microbiota, and their influence on asthma and atopy. Journal of Allergy and Clinical Immunology 128(5):948-955.e3
This was a fascinating read, thank you!