Colostrum |cuh-laas-trum| (noun): the first secretion from the mammary glands after giving birth, rich in antibodies
The amount of research happening right now on microbes and human health is enormous. Think multi-hundred-million dollar, international-collaboration enormous. I’m sure the interest has been building for a long time, but the game changer I’m aware of is Ley et al. (2005), which showed that bacterial communities in obese mice were statistically similar to those from other obese mice and statistically different from normal-weight mice. Turnbaugh et al. (2006) showed that the shift that occurs from normal to obese* microbial communities favors microbes that are more efficient at extracting energy from a given amount of food. I’ll repeat that part: obese individuals extract more calories from a given piece of food than normal-weight individuals extract. The obese individuals have lower bacterial diversity, a trait that has also been linked to allergies. The childhood obesity epidemic is of particular concern to us all – up to a third of American children are obese and the detrimental health effects of this disease are well documented. Having a well-functioning gut microbiota may be a key to healthy weight.
That brings me to today’s topic: human breast milk (which I’ll refer to as HBM for the rest of the post). Cabrera-Rubio et al. (2012) analyzed the bacterial composition of HBM from 18 women at three time points over 6 months. The mothers in the study varied in weight and delivery method. The researchers were basically exploring what factors influence the microbial composition in breast milk, with an emphasis on weight of the mother. They used next-generation sequencing to produce a library of sequences that were analyzed for what specific bacteria were found in each sample and how the samples relate to one another as whole communities.
COOL RESULT 1: HBM is a unique community when compared to other human-body-microbiota. This isn’t that surprising – many places across the human body have distinct bacterial assemblages (back of the knee, ear canal, right hand, left hand, nostril, etc.) – but it is an important first step in studies like this.
COOL RESULT 2: HBM was sampled three different times: immediately after birth (colostrum), at 1 month post delivery and 6 months post delivery. The colostrum was compositionally distinct from the other HBM samples. Babies are born with a sterile digestive tract – every one of us obtains our bodies’ beneficial microbial communities from scratch. Exactly how babies go from a sterile gut to a functioning human-specific gut community isn’t thoroughly understood. Wouldn’t it be cool if HBM has evolved to go through some sort of successional process that changes bacterial composition as the baby matures? (For the record, I’m not sure how much evidence supports this theory, I just like the thought of it and don’t think it’s beyond the realm of possibility.)
COOL RESULT 3: Colostrum and 1 month HBM from the obese mothers had lower bacterial diversity than the normal mothers (but there was no difference in the 6 month milk). It’s not really known where the bacteria in HBM come from. One possible explanation is that the baby, after being inoculated by the birthing process, transfers bacteria back to the breast, and thus, the breast milk. This is supported by another result of the study – an increase in common oral bacteria in the 1-month and 6-month HBM, suggesting a transfer and cultivation of the baby’s mouth bacteria to the breast of the mother. Wherever they come from, the lower diversity finding implies that babies of obese mothers might be receiving a gut microbiota that is pre-adapted to obesity.
COOL RESULT 4: It has been previously published that babies who have been C-sected have a different fecal microbiota than vaginally-delivered babies. This makes sense, since regular birth is a thorough dousing of mom’s vaginal microbiota and Caesarian section is done in a pretty sterile manner (relatively speaking). Cabrera-Rubio et al. also found HBM from mothers with planned C-sections was different from mothers who vaginally delivered their babies. This further supports the idea that babies might transfer bacteria back to the mother after birth. BUT! Prepare yourself for the thing that blew my mind the most:
COOL RESULT 5! Non-planned C-section HBM was way more similar to vaginal delivery HBM than the planned C-section HBM. WHAT?!?!? The authors posit that something about the hormonal processes that occur during labor has a direct influence on the microbial composition of the milk. Hormones or stress or something like that. The mothers who planned a C-section and never went into natural labor did not experience the same physiological processes and this manifested in different HBM.
I never thought I’d be this interested in breast milk but I find this absolutely fascinating. Evolution is amazing! If HBM is so chock full of good bacteria, maybe I should be adding colostrum to my morning coffee. (Ok, that crossed a line. Ew. I apologize.)
*Obese = BMI > 30.
Cabrera-Rubio, R., M. C. Collado, K. Laitinen, S. Salminen, E. Isolauri, and A. Mira. 2012. The human milk microbiome changes over lactation and is shaped by maternal weight and mode of delivery. The American Journal of Clinical Nutrition 96:544-551.
Costello, E. K., C. L. Lauber, M. Hamady, N. Fierer, J. I. Gordon, and R. Knight. 2009. Bacterial community variation in human body habitats across space and time. Science 326:1694-1697.
Hanski, I., L. Von Hertzen, N. Fyhrquist, K. Koskinen, K. Torppa, T. Laatikainen, P. Karisola, P. Auvinen, L. Paulin, M. J. Makela, E. Vartiainen, T. U. Kosunen, H. Alenius, and T. Haahtela. 2012. Environmental biodiversity, human microbiota, and allergy are interrelated. Proceedings of the National Academy of Sciences 109:8334-8339.
Ley, R., F. Bäckhed, P. Turnbaugh, C. Lozupone, R. Knight, and J. Gordon. 2005. Obesity alters gut microbial ecology. Proceedings of the National Academy of Sciences 102:11070-11075.
Turnbaugh, P., R. Ley, M. Mahowald, V. Magrini, E. Mardis, and J. Gordon. 2006. An obesity-associated gut microbiome with increased capacity for energy harvest. Nature 444:1027.