New research shows that Bifidobacteria transfer from mother to child

Both natural birth (as opposed to birth by C-section) and breastfeeding are topics that stir up a lot of conversation among mothers and the scientific community. For example, there is the question of whether breastfeeding rather than formula feeding has some specific benefit to an infant’s health. Well, what about the infant’s gut microbial health? A new article published by Applied and Environmental Microbiology takes a look at whether natural birth and breastfeeding coincides with an exchange of bacteria from mother to child.

Four mother and infant pairs were included in the study that was meant to discover whether the mother transfers any bacterial strains to the infant during vaginal birth and breastfeeding. In particular, the scientists were looking at the genus Bifidobacterium because this group has been known to be early colonizers of the infant gut. In addition, this genus has specific ways of digesting a human mother’s milk. Mother-infant pairs 2 and 4 exclusively breastfed, while pairs 1 and 3 supplemented with formula. Milk samples were collected from the mothers and fecal samples were collected from the mothers and children.

After sequencing the bacteria, B. adolescentis, B. angulatum, B. breve, B. dentitum, B. pseudolongum and B. thermacidophilum were found to be common between all of the mother and the infant fecal samples. The scientists then looked to see which bacteria were in both the mother’s milk and the infant’s fecal sample. The results suggest that the milk may be responsible for transferring B. adolescentis, B. angulatum, B. breve, B. longum and B. pseudolongum to the infant. Interestingly, there were also some bifidobacteria strains that were unique to the infant, suggesting that either they went undetected in the mother or that the infant was exposed to this bacteria from somewhere else.

After six months, samples were collected again in order to see how/if the sample compositions change. The scientists found that, especially in the infants, the abundance of bifidobacteria decreases. This is most likely due to changes in diet – less breastfeeding and more formula feeding – and perhaps environmental exposure. All in all, the results of this experiment shows that the infant microbiome might indeed be influenced by a vertical transfer of bacteria from mother to child. With more evidence of this as a possibility, science may begin looking into more complete analyses with larger study sizes.  

Breastfeeding associated with intelligence later in life

Positive association between breastfeeding and intelligence, between three tiers of family income.  Five IQ points is 1/3 of a standard deviation. 

Editor’s note: I would like to tread very lightly on this topic because of the complexity of the relationships between all the factors discussed and the implications a study like this has.  I probably would not have written about it at all, had it not been published in such a prestigious medical journal, and had been as comprehensive as it was.

Breast milk is the ultimate pre- and probiotic.  It is essential in developing infants’ microbiomes by inoculating and enriching their guts in certain bacterial species.  There have been a number of studies showing alterations of the gut microbiomes of infants that are formula fed, and other studies showing that formula feeding results in a higher risk of asthma and allergies later in life.  The complicated relationship between breastfeeding, the microbiome, and phenotypes like autoimmune diseases are not understood at a mechanistic level.  Still though, it appears that formula feeding, rather than breastfeeding, may have long term consequences for the health of a child.

To that end, there had been a few small scale studies that demonstrated a general association between breastfeeding an IQ.  Just last week, a new study, much more comprehensive than any previous one, delved into this topic and found the same result: duration of breastfeeding was positively associated with IQ, educational level, and income.  The results of this study were published in The Lancet.

In 1982 researchers from Brazil began a longitudinal study using a cohort of over 500 newborn infants.  At that time, one of the things the scientists measured was the duration that each infant was breastfed.  Then, in 2012, the researchers followed up with 3000 of those people in the original study and surveyed them for their educational levels and incomes, as well as measured their IQs.  They discovered that each of these three variables was directly related with the length of breastfeeding, with the possibility that over 12 months of breastfeeding actually slightly decreased each.  Even after factoring in confounding variables such as maternal education, family income, and birthweight the relationship between breastfeeding and IQ, education, and income still held.  The researchers acknowledged the link was tenuous, and that there exists a whole host of other important variables that were not measured in 1982.  Nevertheless, the study suggests that breastfeeding improves intelligence upon adulthood.

Breastfeeding, if possible, is clearly preferred to formula feeding, and studies like this show that it may be in everyone’s interest to promote breastfeeding children.  It will be necessary to decipher the connection between breastfeeding, the microbiome, and these observations, but with more studies in the pipeline showing the value in breastfeeding everyone should be aware of its importance.

Breastfeeding plays an important role in microbiome development

As soon as a child is born, his or her microbiome is continually being shaped by external factors such as diet and bacterial exposure. The first few years of life are critical in microbiome development as these early years will shape the composition of bacteria that will inhabit that individual’s body for years to come. Infant dietary habits play a critical role in this development.  Breast milk has high nutritional content and is important in passing immunological factors from mother to child, as well as nutrients that are essential for gut colonization by bacteria. A team of scientists led by a group at University of North Carolina School of Medicine published in Frontiers in Cellular and Infection Microbiology on early changes and development of the microbiome in infants with different feeding and daycare habits.

Stool samples were collected from nine infants, some of which were exclusively breastfed (EBF) and some of which were non-exclusively breastfed (non-EBF). The infants were followed over a period of time from 2 weeks to 14 months, and samples were collected before and after the introduction of solid foods. The samples were tested for differences in bacterial composition.

The scientists found that infants that were solely breastfed and did not receive formula had guts that were more prepared for the introduction of solid foods. When solid foods were introduced to their diets, the microbial shift was much less dramatic than the shift for infants who were breastfed while also receiving formula.

Analysis showed that non-EBF infants had greater microbiome species diversities compared to EBF infants. Also, non-EBF infants showed lower abundances of Bifidobacterium and greater abundances of Eggerthella compared to EBF infants. Bifidobacterium is a bacterium that is associated with good digestion. After introduction of solid foods, however, EBF infants showed an increase in Eggerthella abundance, and non-EBF infants showed an increase in Bifidobacterium abundance.

In a second part of the study, researchers considered day care attendance when comparing the microbiome of the infants. They found that attending daycare resulted in a more diverse microbiome, but feeding habits were the most important factor for microbiome composition after the introduction of solid foods. 

It is clear from this study, in addition to others  we have discussed, that there are many factors contributing to microbiome diversity and species richness. This study highlights the important role that diet plays on early microbiome development. What was quite interesting was that while many studies often equate a more diverse microbiome with health, the infants that were exclusively breastfed had less diverse microbiomes yet they were more prepared for the introduction of solid foods.  This study only included nine participants and should be expanded to include a greater number of infants to better understand this relationship, but it can still help inform the conversation around breastfeeding versus formula feeding. 

Reflecting on the microbiome during National Breast Cancer Awareness Month

As you watched the future Hall of Fame quarterback Eli Manning over the past two weeks, you probably noticed NFL players wearing pink for National Breast Cancer Awareness Month. Before this month comes to a close we want to bring your attention to one of our previous posts about the microbiome and breast cancer.  The study showed that post-menopausal women who had a more diverse gut microbiome had a lower risk of getting breast cancer. You can read more about it here.  

We also want to take this time to encourage natural breast feeding, whenever possible, for all new mothers.  A new review article published in Nature Pediatric Research describes the importance of breast milk in creating a healthy infant microbiome.  Breast milk is a complex food that contains bacteria and also supports the growth of bacteria.  The review highlights that when compared to formula, breast feeding leads to more infant gut colonization of Bifidobacterium, Lactobacillus, and Clostridia, and these bacterial strains are linked to the development of a healthy gut and a healthy immune system.  In addition, breast milk leads to a lower infant gut pH, compared to formula, and infant gut pH affects further species colonization.  Breast milk has evolved to support both us and our microbiomes, and no simple formula can substitute for the real thing.  

Every week there are new studies connecting the microbiome to public health and disease areas that may not seem as obvious as others. We know that the microbiome influences diseases and conditions like obesity, inflammatory bowel disease (IBD), diabetes, and necrotizing enterocolitis (NEC), but we are now learning that the microbiome is also connected to diseases and conditions like breast cancer, alcoholism, autism, and depression. While it is important to keep our excitement about the microbiome in check, the AMI is building new resources for the microbiome field because we believe our impact can be vast.  Advancing the field of research as a whole can influence the development of new treatments and therapies for a wide range of diseases. 

Caesarean sections, breast feeding, and the microbiome

There is a growing amount of literature on the subject of babies' microbiomes because it is clear that the first few years of life are crucial to the development of the immune system, and poor development can have lasting, life-long consequences.  As we have learned, a healthy microbiome is absolutely critical to a healthy immune system.  Evidence for this connection is vast, but starkly manifests itself in germ-free mice which can not survive long due to autoimmune disease.  So, as the thinking goes, a healthier microbiome as a baby leads to a healthier life.

In any case, a commentary was recently written by AMI Scientific Advisory Board members Maria Gloria Dominguez-Bello, Rob Knight, and a colleague that discusses how delivery mode and infant feeding affect babies' microbiomes.  As it turns out, epidemiological studies on large human populations have correlated Caesarean Section (C-section) delivery to obesity, asthma, celiac disease and type 1 diabetes, which are all autoimmune diseases.  Breast feeding, on the other hand, leads to decreased risk for some of these same diseases.

Research has shown that both C-section and breast feeding have a direct and significant influence on an infant's microbiome.  During vaginal delivery the child's gut is inoculated with the vaginal microbiome, whereas in a C-section the child's gut is associated more with the skin microbiome.  In addtion, breast feeding contains prebiotics that encourage certain bacteria to grow, which selects for a specific infant gut microbiome.  

Interestingly, the authors mention a study that showed the microbiota from the breast milk may actually be different depending on the mode of delivery.  They also comment on a study that showed certain gut bacteria are found in the vaginal microbiomes of pregnant women, as if prepared to inoculate the child.  This is in agreement with another study from Jacques Ravel which I have already blogged about.

It is very important to consider the microbiome when a woman is giving birth and feeding.  If a C-section is required it may be possible to inoculate the child's gut manually, and studies are currently investigating this.  The results of these studies will be the topic of a future blog.