So is breast truly NOT best on the long-term?

Yesterday, a new study came out on the long-term effects of breastfeeding. The major limitation of this kind of research is that sociodemographic factors are so intertwined with breastfeeding behavior and long-term outcomes that it is nearly impossible to correct for this statistically. So Cynthia Colen did something smart: she looked at families in which one sibling was breastfed while the other wasn’t and in this way was able to circumvent all the unknown confounding factors. Her results have been highlighted on many news websites because they show that there are virtually no long-term benefits of breastfeeding. The most important findings are explained here by The Skeptical OB.

However, when I read the paper I couldn’t find one important piece of information: how long did these mothers breastfeed for? In this news article it says an average of six months, but those data (and the standard deviation) are nowhere to be found in the paper (or is it me and did someone else find them?!). The authors of the paper do report that there is no correlation between the long-term outcomes and the duration of breastfeeding, but since an average of six months is a lot less than the AAP recommended year, I still wonder if we can draw these conclusions from this study. Another piece of information that I missed is if in the discordant sibling sample, the first sibling was more likely to be breastfed than the second or the other way around. I want to know these things so I can judge this paper better!

An important factor that I’m missing in the current news reporting on this paper is that breastfeeding does seem to have short-term benefits for children and both short- and long-term benefits for mothers (well of course journalists aren’t known for their nuance, but still).

So don’t get me wrong: I think it is super important to have real and reliable data in order to create recommendations for breastfeeding and whether or not we should encourage women to do so. I recognize that starting to breastfeed can be a huge struggle and it is important to have the right information. But I feel that the societal debate that is happening following the publication of this article misses these points A LOT.

 

Reference:

Is Breast Truly Best? Estimating the Effects of Breastfeeding on Long-term Child Health and Wellbeing in the United States Using Sibling Comparisons. Cynthia G Colen, David M Ramey. 2014 Social Science & Medicine, available online Jan 29 2014

Advertisements

15 Comments

Filed under attachment parenting, baby, breastfeeding, maternity leave, parenting, pumping milk

15 responses to “So is breast truly NOT best on the long-term?

  1. I wonder if there’s anything of this sort with twins? I had an informal mentor who started the Vietnam Era Twins Registry for just such epidemiological studies. Seems like you could do it maybe with identical-twin moms: one who breast fed and one who didn’t?

    • I wonder how many people would breastfeed one twin but not the other, but you’re right that that would be the perfect control. I do know of this picture that circulated on Facebook of a mother in some developing country who thought she would only have enough milk to breastfeed one twin and formula fed the other. Since the water was contaminated the formula fed twin looked way thinner and smaller than the breastfed twin, but this is anecdotal and not a very good control of course.

      • That’s why I was thinking the moms would be the twins. One mom breast feeds, the other doesn’t? Might find those naturally for a case-control study.

      • Oh sorry I misunderstood your suggestion. In the case that one twin breastfeeds and the other doesn’t you would still need to control for demographic factors, that could be both the cause that one decides to breastfeed and the other doesn’t AND the reason the kids might show differences on the long-term.

  2. Kimberly

    I agree, there should be much more data available, particularly regarding duration of breastfeeding. I don’t think a study with a breastfeeding period that is HALF of the AAP recommended 1 year can legitimately say much regarding long-term benefits.

    Also, in regards to your title, I don’t think the author is implying that breast is not best, just equal. Your title makes it sound as though it is being suggested that formula is actually better, which just makes me shudder. :O)

  3. tsanbukh

    To clarify the questions you want answered and the reasons you think these questions are important:

    1) For breastfed babies, what is the duration of breastfeeding and how (if at all) does that correlate with improved outcomes? Your implied hypothesis is that even if there is no substantial long-term benefit to breastfeeding for 3 or 6 months, there may be a substantial long-term benefit that can only be incurred by breastfeeding for 9 or 12 months or longer. (This despite knowing that the fraction of total calories derived from breast milk only decreases over time – on its face, this is not a strong hypothesis.)

    2) For discordant sibling pairs, does birth order correlate with breastfeeding status, and if so, how? Your implied hypothesis here is that it does correlate, AND that this correlation confounds the results reported – ie, mothers are more likely to formula feed a firstborn child but firstborns have better outcomes overall. This is an interesting idea but I don’t see that answering the birth order correlation question would give you enough information, unless we also have information about whether and how birth order correlates with long-term outcome.

    My question for you is, why do you think these things really matter?

    The study well-supports the authors’ conclusion that women who want to breastfeed should be supported in doing so for as long as they want to, and that other women should not worry or feel guilty about not breastfeeding or about stopping breastfeeding because any concrete long-term benefit to the child is small.

    The questions you pose do not seem to contradict this conclusion – neither set of questions has any ability to unmask a previously-hidden clear and large effect. So evaluating the paper should lead to the same conclusion: women should breastfeed if they want to with plenty of support, and parents who don’t breastfeed should not believe that their children will suffer for it.

    • Re 1: I would like to know if the mothers that responded “yes” exclusively breastfed or maybe supplemented with formula. Because the way the question is asked suggests that even if they breastfed for 1 week and then formula-fed, they would still fall in the “yes”-group. Even though the breastmilk intake decreases over time, I’m not sure if there is a big drop after 6 months. Introduction of solids does not happen overnight, so that second half of the first year may be just as important as the first half.

      Re 2: the authors say that they control for birth order, I’m just curious as to whether birth order matters and whether more first-borns are breastfed than second children. I don’t have a clear hypothesis, I would just like to see the data that they say they use.

      I think the paper is very interesting in that it uses a new way to study the long-term effects of breastfeeding. However, in order to draw these conclusions and make recommendations about breastfeeding I think it is important to know whether these results from 1 paper from 1 cohort of people remain true with more research.
      I don’t want anybody to feel guilty about breastfeeding or not, I just think that if you use science to make your decisions, it should be good science.

  4. tsanbukh

    Re: duration of breastfeeding:

    Excerpts I have seen suggest that the paper, which is long and to which I am still working on getting access (so I haven’t read it), goes into some detail about the effects of additional weeks of breastfeeding.

    Relatedly, we don’t have to wonder about the breast-milk-consumption-versus-age curve; that work has been done many times, and a small amount of google-scholaring brings up a healthy array of relevant studies about infant energy intake from breast milk and solid foods as a function of age, both in descriptive and interventional studies.

    Regardless, whether or not infants at (say) eight months of age are still deriving an important fraction of their energy from breast milk is an entirely different question from whether or not they are still deriving any unique benefit from the breast milk. Some people (I don’t know if you are among them) believe that breast milk consumed by a child of any age always has a positive effect beyond the effects of the energy, protein, and fats it contains. The competing hypothesis is that the special effect of breast milk is strongest in the neonatal (or even premature – evidence strongly supports exclusive breast milk for preemies, as I’m sure you know) period, and wanes thereafter at a rate that is not necessarily exactly correlated with the fraction of total energy a breast-fed baby derives from breast milk.

    Re: birth order and control:

    http://blog.minitab.com/blog/adventures-in-statistics/a-tribute-to-regression-analysis

    Or, shorter and more snarkily:

    http://xkcd.com/1138/

    I don’t understand why you would want to see the raw data unless it is to run your own confirmatory calculations on it. If the variable (birth order) needs to be controlled for and has been, then you don’t gain anything other than confusion by looking at the data without the confounder accounted for.

    Listen, I am pro-breastfeeding. I think anyone who wants to do it should be fully supported in that. But I think your criticisms here are weak.

    • Yes you’re right that the paper looks at it both ways: with breastfeeding as “yes” and “no” and taking the amount of weeks into account. However, as I read the paper, “yes” does not mean exclusively breastfed, but just “ever breastfed”. Also, when taking into account the amount of weeks breastfed, they see no difference with the binary approach, which leads them to conclude that it doesn’t matter if you breastfeed for longer or shorter amount of time. However, they do not state anywhere HOW long these women breastfed for. The news article says an average of six weeks but the authors fail to report this in the paper although in my opinion that is very important information to judge whether their conclusions are valid.
      This isn’t about being pro-breastfeeding or not, it’s about being able to judge a scientific paper.

  5. Pingback: Is Breast Best? Does it Matter? | Professor Doctor Mommy

  6. This came in my email today. Different author. Same sibling instrument, completely different results. (Note that it does look at length of time breastfeeding and suggests that duration is important):

    http://www.nber.org/papers/w19940?utm_campaign=ntw&utm_medium=email&utm_source=ntw

    Breastfeeding and Child Disability: A Comparison of Siblings from the United States
    George L. Wehby
    “Little is known about whether breastfeeding may prevent disabilities throughout childhood. We evaluate the effects of breastfeeding on child disability using data from the National Survey of Family Growth merged to the National Health Interview Survey for a large nationally representative sample of children aged 1 to 18 years from the U.S. including over 3,000 siblings who are discordant on breastfeeding status/duration. We focus on a mother fixed effect model that compares siblings in order to account for family-level unobservable confounders and employ multiple specifications including a dynamic model that accounts for disability status of the prior child. Breastfeeding the child for a longer duration is associated with a lower risk of child disability, by about 0.2 percentage-points per month of breastfeeding. This effect is only observed on the intensive margin among breastfed children, as any breastfeeding has no effect on the extensive margin. We conclude that very short breastfeeding durations are unlikely to have an effect on reducing disability risk.”

  7. jimwoodgett

    Have you seen this study? PMID: 23154192 The impact of breastfeeding on FTO-related BMI growth trajectories: an application to the Raine pregnancy cohort study.

    Several of our scientists were involved in it (thats how I know about it, not my field!) and the data looked strong to me. However, breastfeeding was protective to specific alleles, so if the baby didn’t have the detrimental allele, there was little impact.

    • Thanks for your comment! That is an interesting study looking at GxE interactions. I guess what bugs me the most is that there is a plethora of studies out there but just this one gets all the media coverage which makes people believe that this is the only study there is.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s