The science of breastfeeding

In the interest of full disclosure, I want to start off by stating a few facts about my own experience breastfeeding.  I nursed my daughter, Mable, for the first year of her life.  She weaned around her first birthday.  When I went back to work after my three-month maternity leave, we started supplementing Mabel’s diet with formula since I wasn’t able to pump enough.  I was lucky to have workplaces that were supportive of nursing mothers- both had a nursing mother’s room.  While I did take a valuable breastfeeding class (with my husband) before Mabel was born, I was also lucky that my daughter was a champion nurser- from the first moment, she latched on perfectly.  I never had any pain (aside from two minor blocked pores), it was not a struggle, it was easy. 

I know that my experience is unusual.  I did not anticipate it being easy- I took the class and mentally prepared myself for a challenge, reminding myself, frequently, that there would be a learning curve for both she and I, so I had to be patient.  While it was easy for me and my daughter, I know that other moms and babies don’t have it that easy.  I know nursing is not for everyone.  I commend moms who try hard.  I commend moms who won’t give up, no matter what.  I also commend moms who know when to give it up and get on with the business of mothering, refusing to let breastfeeding rule their lives and prevent them from enjoying their children.

I recently saw this report from the CDC:  Breastfeeding Report Card, 2010.  Looking at the figure below, I’m pretty sure the US failed, miserably.

2010 CDC Breastfeeding Report Card.   Percentage of Children Who Are Breastfed at 6 Months of Age

Now, I know full well that correlation does not mean causation, but I was struck that the lowest rates of  breastfeeding corresponded to states that routinely battle poverty and obesity.   There are probably a host of contributing factors- access to health-care, maternity leave policies, supportive workplaces, mother’s age, mother’s education level, breastfeeding support/education, etc.  While I will not claim that there is a causal link there, for practical reasons, getting moms to breastfeed in those states would be beneficial.

For one, breast milk is free.  Avoiding the expense of formula for a family that is already struggling financially would make sense, and certainly financial benefits factored into my strong desire to breastfeed (Although saying breast milk is free ignores the cost of a breast pump or assumes insurance that will cover renting one).  Also, there is mounting evidence for the molecular mechanism(s) by which breastfeeding can decrease the likelihood of a child becoming obese or diabetic.

Since I could spend a month researching the possible causes for the numbers on that report card above, I’m going to glance over the reasons why that map looks the way it does- we can all agree that our nation has to step up and do a much better job to encourage and support breastfeeding and motherhood in general.  Instead, I’d like to break down some of the science I mentioned.  How is it that breastfeeding/breast milk is so much different from formula?  Aren’t nutrients just nutrients?  Here we go…

Human milk feeding is associated with substantial benefits to the premature infants’ health. Mother’s own milk with nutrient supplementation is associated with reduced infectious and inflammatory disease, enhanced neurodevelopmental outcome, and, in a carefully designed nutritional program, is associated with healthy early postnatal growth patterns.  (Heiman and Schanler Early Human Dev. 2006)

There are compelling data that breast milk decreases risk of obesity, supports brain development, helps regulate the immune system, prevents infections, and decreases instances of asthma (and here).  However, there are mixed results on whether or not breast feeding helps prevent Type 1 diabetes.  So how does this work?

I did feel more comfortable using a nursing cover (I have a Hooter Hider"") for nursing in public.

Breastfeeding and obesity

There are lots of things in breast milk- not just nutrients like fats and proteins, but molecules that instruct the behavior of cells, like hormones.  In regards to obesity, hormones like leptin and adiponectin, that influence appetite, are found in breast milk and may function to help infants regulate their food intake.  Behaviorally, breastfed babies control the amount of milk they consume and may be regulating their food intake better than a caregiver with a bottle of formula that would go to waste if baby wasn’t coaxed to finish it.  There’s also the possibility that mothers/families that choose to breastfeed are more health-conscious and therefore generally live a healthier lifestyle.

None of these data depict the whole story- there is much that remains unknown about how breastfeeding decreases the incidence of obesity, and breastfeeding is by no means 100% effective in that regard (I’m an obese adult who was exclusively breast-fed for the first year of my life).  The take home message is that the components of breast milk- the hormones and growth-factors- and the self-regulated food intake may influence the brain and the digestive tract of the infant to appropriately regulate food intake and or body weight all the way into adulthood.  (Source:  Savino et. al. Int. J. of Ped. Endocrinology 2009)

Breastfeeding and IQ

This benefit is definitely not a straightforward one.  Intelligence is difficult to measure/assess and even if there was a clear metric, determining the contribution of each influencing factor would be impossible (at least by current available methods).  Data have been published supporting the theory that fatty acids in breast milk support brain development or just make for larger brains, that close maternal contact reinforces neural connections, etc.  I think right now science doesn’t have the tools to definitely state which is the case.

Breastfeeding and the immune system

The immune system is designed to respond only to foreign bodies (germs, viruses, bacteria, etc), however, sometimes the immune system over-reacts to something foreign (like a bee sting or a peanut allergy) or even reacts to something that is normally present in the body (auto-immunity).  There are also instances where too much inflammation can cause illness, like eczema or asthmaDiabetes (Type I) is a result of auto-immunity, the body’s immune system attacks insulin-producing cells, resulting in a person unable to make insulin and properly metabolize sugar.

So how can breastfeeding prevent these inappropriate immune responses?  Cytokines.  Cytokines are molecules that can bind to cell surface receptors and control the activity of immune and other cells.  There is mounting, convincing evidence that the cytokines in breast milk,  like TGF-beta, help to modulate the immune system.  TGF beta can both promote an immune response, as well as help to calm the immune system.  The current theory is that cytokines in breast milk help keep a newborn’s immature immune system in check- encouraging it to respond only when it’s appropriate, and preventing it from over-responding when inappropriate.  By preventing an over-response, either auto-immune, in the case of diabetes, or inflammatory, in the case of asthma, cytokines may be the reason breastfed children have a lower incidence of diabetes and asthma.  (Reference:  Oddy et. al. Pediatric Allergy and Immunology 2009)

Another way that breastfeeding supports the immune system of newborns is by filling in for a baby’s immature immune system.  Breast-milk contains a large number of antibodies produced by the mother.  Some of those antibodes guard against bacteria and viruses that normally cause gastro-intestinal illnesses like rotavirus.  Some antibodies coat the lining of the intestine (which is also immature- hence waiting until 4 to 6 months to give babies solids and cow’s milk) and prevent things like germs from getting out.  These antibodies may also prevent food allergies by keep food particles from leaking out of the intestinal track.  There are also mechanisms that allow maternal antibodes in breast milk to pass through the lining of the infant’s intestine and enter the circulation.  There, the antibodies can help the infant’s immature immune system respond to infection.  This mechanism of supporting the immune system is the major way that breastfeeding is thought to decrease the incidence of childhood illnesses like ear infections and diarrhea.  (Reference:  Van de Perre, Vaccine 2003)

In addition to these cytokines and antibodies, breast milk, particularly colostrum (the very first milk produced when the baby is born), is loaded with white blood cells.  These cells from the mother are active in the baby’s gut, attacking bacteria themselves, as well as encouraging the cells of the baby’s immune system to respond to infection.  There is an excellent article from Scientific American that does a much more detailed, yet easy to read, job of explaining how breast milk supports a baby’s immune system here.

This is what I call breastfeeding support!

The tip of the iceberg

This is really just a brief summary of the ways that breastfeeding and breast milk are good for babies.  I hope it can help encourage moms who are struggling, with their newborns, to learn to breastfeed, or help to motivate moms-to-be who are on the fence.

I only have two pieces of advice for moms and moms-to-be: 1) take a breastfeeding class WITH your partner, 2) expect it to be a challenge.

After I had Mabel, 36 hours of labor and C-section left me completely out of it.  When Mabel and I were reunited in the recovery room, all I could do was lay there and stare at her.  I was confused and awe-inspired and otherwise useless.  The nurse quickly said it was time to put Mabel to the breast and I just laid there.  While Mac held Mabel, the nurse loosened my gown.  Then, she and Mac (and Mabel) proceeded to do everything for me.  I am so grateful he went to the class with me and knew what to do.  In those first few days, he routinely helped me to recall what we had learned.  It was invaluable support.

As for the second piece- both you and your baby have to learn how to breastfeed.  Yes, babies are born with a natural reflex to suckle, but how to latch and nurse efficiently takes practice.  How to get the baby to latch and nurse efficiently takes practice.  There are techniques and approaches for getting it right.  Take advantage of breastfeeding resources like the lactation consultant and nurses at your hospital, your local La Leche League, local hospital breastfeeding/new mom support groups, etc.  Find out about these resources ahead of time, so they are at your fingertips when things aren’t going smoothly.  Overall, remember that there is a learning curve, for both of you, and try to be patient (with yourself and your baby) in those early days and weeks.

It shouldn’t go without saying that all of this advice is great, but breastfeeding isn’t for every mother and baby.  Sometimes there are anatomical barriers (inverted nipples, breast reduction/enhancement surgery, cleft palate, tongue-tied, etc.) that can make it harder or impossible to breast feed.  Sometimes a baby just can’t learn to latch well, a mom doesn’t make enough milk, mastitis, thrush, etc.  There are plenty of things that can go wrong.  Moms should get all the support they need to try and breastfeed.  The should also get all the support they need in making the decision to forgo breastfeeding- either to pump and bottle feed, or switch to formula.  There are plenty of healthy, happy, bottle/formula fed babies out there, with happy, healthy moms.


Filed under Mother, Scientist

6 responses to “The science of breastfeeding

  1. Pingback: The science of breastfeeding | Kids say :

  2. jackie o

    I found this entire article very interesting! Thank you for all your hard work that went into writing it!

  3. I found you through Kelly’s Korner and am really enjoying reading your posts! Love your worldview 🙂

  4. Pingback: A day in the life of a Sci-Mom | mommacommaphd

  5. Pingback: The Transition to New Motherhood | mommacommaphd

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