A peanut butter sandwich may seem innocuous, but for a growing number of children, it may be harmful or even life-threatening. Food allergies to peanuts, tree nuts and shellfish cause the most severe reactions but eggs, milk, wheat and soy are also on the list of potential antigens.
Food allergies in children are becoming more common. So too are deliveries of babies by cesarean sections (CS) across the globe, rising alarmingly above the World Health Organization proposed ideal rates between 10-15%.
These trends may be related, linked by altered gut microbiota.
Because they are not exposed to maternal vaginal microbiota, babies delivered by CS host a different colonization pattern of the gut microbiota. These CS-induced alterations are associated with an altered immune development that may manifest as food allergies.
Food allergies are one among many immune-mediated diseases in young children in which altered gut microbiota at critical stages of early life have been suggested to influence later risks of allergic diseases. Moreover, several epidemiological studies have shown that the composition of gut microbiota differs between allergic and healthy children.
However, little is known about just how CS-induced changes in the gut microbiota can lead to food allergies.
A 2021 study looked at the impact of CS on experimental food allergy in rats and if probiotic treatments could reverse such effects. First, here’s an update on CS.
Cesarean sections, prevalence and risks
While this delivery mode saves lives when medically indicated, overuse is rife in developed countries: CS use is almost five times more frequent in births in the richest versus the poorest quintiles in low-income and middle-income countries.
CS may lead to adverse short- and long-term health effects. Notably, CS is a surgical procedure with higher risk of maternal and child death than vaginal birth. Babies born by CS have different hormonal, physical, and bacterial exposures, which can increase risk of immune-mediated diseases, including allergies, asthma, inflammatory bowel disease, eczema, atopic dermatitis, respiratory infections and obesity.
Cesarean section and gut microbiota
CS delivery leads to a distinct pattern of microbiota colonization in newborns, exhibiting a lower relative abundance of vaginal bacteria and a higher level of opportunistic pathogens associated with the hospital environment. Note that in addition to mode of delivery, feeding type, antibiotics, and environmental exposures shape the newborn gut microbiota, all of which can have enduring health consequences for the offspring.
Intestinal microbiota has an important role in signaling the developing mucosal immune system. The hygiene hypothesis suggests that reduced exposure to microbial stimuli in early life programs the immune system toward a Th2-type allergic response.
One study showed that vaginally delivered infants acquired bacterial communities resembling their own mother’s vaginal microbiota, dominated by Lactobacillus, Prevotella, or Sneathia spp., and CS infants harbored bacterial communities similar to those found on the skin surface, dominated by Staphylococcus, Corynebacterium, and Propionibacterium spp.
Another study revealed that the most abundant bacterial species present in vaginally delivered infants were Acinetobacter sp., Bifidobacterium sp. and Staphylococcus sp. but CS infants’ fecal microbiota was dominated with Citrobacter sp., Escherichia coli and Clostridium difficile.
Intestinal dysbiosis has been shown to precede the onset of clinical allergy, possibly through altered immune regulation.
A number of clinical studies have investigated the potential of probiotic bacteria to ameliorate the pathological features of allergic disease including food allergy. For example, probiotics have shown both preventive and therapeutic benefits in cow’s milk protein allergy.
Prebiotics and synbiotics are also being explored as potential beneficial substances in food allergy.
Food allergies and microbiota
CS-induced changes in the gut microbiota can lead to food allergies. Gut microbiota plays a critical role in food allergies but exact mechanisms by which CS changes cause food intolerances are unclear.
A new study looked at the impact of CS on experimental food allergy in rats and if probiotic treatments could reverse such effects. A rat model of CS delivery was used to compare the severity of mice sensitized by ovalbumin (OVA)-induced food allergy between rats delivered vaginally and by CS. Subsequently, a mixture of Lactobacillus acidophilus, Bifidobacterium longum subsp. infantis, Enterococcus faecalis, and Bacillus cereus was administered to rat pups from birth.
- CS increases disease severity in ova-induced food allergy
- CS dysregulates the expression of tight junction proteins and upregulates the levels of Th2 cytokines
- Food allergy is strongly associated with changes in gut microbiota caused by CS
- Probiotic intervention modulates intestinal microbiota structure of rats delivered by CS
- Probiotics intervention after birth protects CS rats against food allergy
The authors concluded that intestinal microbiota plays an important role in the food allergy model of CS rats, and probiotic intervention appears to be an effective strategy for the prevention of food allergy in this model. However, probiotic supplementation did not fully correct the gut microbiota dysbiosis. The optimal strains, dosage and duration for supplementation are yet to be determined for clinical applications.
The current high rate of CS delivery has resulted in alterations in microbiota and immunological development, and certain species are crucial throughout critical stages of development. A causal link between the dysbiosis associated with cesarean section and food allergy is emerging. Altering gut microbiota with probiotics may reverse some of that impact. Such an approach may be preferable to vaginal seeding — the mother’s vaginal fluid is used to colonize the newborn gut — which may be ineffective or unsafe.
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