A good friend of mine living in Scotland, who had a baby last year, mentioned to me how disappointed he has been with the U.K. National Health Service’s promotion of breastfeeding. Calling the alleged benefits overstated, he said, is itself an understatement.
I nodded in general agreement, acknowledging that many of the alleged benefits of breastfeeding have only been found in observational studies.
Observational studies on breastfeeding merit skepticism, because they all suffer from the same major problem: breastfed infants on average differ from formula-fed infants not just in how they are fed in infancy, but in practically every other possible way–maternal education, maternal IQ, poverty, neighborhood safety, exposure to environmental toxins, race, and type and quality of childcare. In scientific terms, breastfeeding is confounded, out the wazoo.
We cannot tell which benefits found in an observational study derive from breastfeeding rather than from the myriad other advantages linked with breastfeeding.
(The “good” observational studies attempt to control statistically for the other relative advantages of breastfed infants. Unfortunately, controlling for confounds only works well when (1) all the important potential confounds are known, and (2) when there is a fair amount of overlap between the groups being compared. Neither of which is true when it comes to breastfeeding.)
In an ideal world, we would settle this question by conducting several large randomized controlled trials (RCTs), in which new mothers would be randomly assigned to breastfeed. RCTs are the gold standard in medicine for determining whether a true cause and effect relationship exists. In practice, though, such trials are neither feasible nor ethical.
Fortunately, we have the next best thing: a handful of studies that have cleverly circumvented the problem of confounding. These fall into two categories:
- sibling studies, which compare siblings from the same families who were breastfed for different lengths of time, or who were not both breastfed.
- a large RCT of a highly successful breastfeeding intervention (PROBIT Trial).
(Is the PROBIT Trial an exception to the no-RCT rule? No. Women in the PROBIT trial were not randomly assigned to breastfed or not; they were randomly assigned to receive a breastfeeding intervention or not.)
After my friend and I spoke about his irritation with the medical organizations like the American Academy of Pediatrics (AAP) and NHS overstating the benefits of breastfeeding, I was dissatisfied with my vague sense that he was right. I wanted to know exactly which benefits had been oversold and exactly which were supported not just by observational studies but by better-designed studies.
The short answer: Nearly all the alleged long-term benefits are likely the result of confounding, not breastfeeding. Better-designed studies find only a handful of real benefits: a reduced chance of severe gastrointestinal infections and a lower risk of eczema during infancy, and perhaps a small boost in childhood IQ.
Alleged Breastfeeding Benefits According to the NHS
According to the NHS, breastfed infants are…
- less likely to suffer from vomiting or diarrhea and therefore less likely to go to hospital
- less likely to develop type 2 diabetes in later life
- less likely to become obese in later life
- less likely to suffer from heart disease in later life
- less likely to suffer from constipation
- less likely to get a chest or ear infection and therefore less likely to go to hospital
- less likely to suffer from tooth development problems
- more likely to have good communication and speech skills
- more likely to have good circulation
- less likely to suffer from wind, colic and constipation
- less likely to develop eczema or asthma
Sounds pretty impressive, right? Until you set aside the evidence from observational studies…
Breastfeeding Benefits Supported By Sibling Studies and A Randomized Controlled Trial
So, let’s start with the good news:
Breastfeeding clearly reduces the risk of severe gastrointestinal infections during an infant’s first year of life. This is true in developed nations, where there is widespread access to clean water, health services, and nutritious food, as well as in developing ones, where the reduction in illness is larger and often life-saving.
The lower risk of infections is also especially important for preterm babies, for whom breast milk substantially lowers the chances of necrotizing enterocolitis, a serious and life-threatening infection.
As for a lower risk of constipation, even though no published research I can find has directly tested this effect, I am inclined to give this one to the NHS. As a formerly breastfeeding mom, I know just how–dangerously and sometimes explosively–runny breastfeeding poops can be.
In terms of benefits that persist into childhood, breastfeeding may also provide a small boost to IQ. The evidence here is not as solid as that for infections, but more compelling than I’d expected. (I will dig further into this complex topic in a moment.)
And now the bad news:
Breastfeeding does not reduce the risk of colic. In fact, I have no idea how this alleged benefit made it onto the NHS’s list in the first place. Most of their alleged benefits are found in observational studies. But not colic. Even most observational studies do not find that breastfeeding lowers the chances of colic.
As for the remaining claims–reduced BMI, lower risk of Type 2 Diabetes, improved circulation, and lower risk of heart disease–there is just no solid evidence to support them. This doesn’t mean that breastfeeding has no effect on these outcomes, but it does mean that we have no reason to believe that it does. And, in my opinion, it does mean major medical organizations should not be stating these benefits as facts.
* * *
The second half of this post is for everyone who wants the nitty-gritty details of the PROBIT trial and the sibling studies–what they found, how they were designed, and what, if anything, were their limitations.
(Skip this section.)
The PROBIT Trial
The PROBIT trial, led by Dr. Michael Kramer of McGill University Medical School, recruited women who gave birth at specific hospitals in Belarus between 1996 and 1997, and who intended to breastfeed. Women were randomly assigned to receive an intervention to boost the rate of breastfeeding (cases) or to standard care (controls).
Why Belarus? It seems an odd choice, but Belarus presented two distinct advantages: First, by the mid-1990s, women in Belarus had the same access to clean water, health services, and nutritious food as women living in other developed nations. So the results of Kramer’s study would generalize to a Western context.
Second, hospitals in Belarus did not yet routinely promote breastfeeding after birth. Their after- birth care was similar to that of most developed nations in the 1940s and 1950s, when formula feeding was in vogue . So Kramer’s breastfeeding intervention would likely have a large impact.
By any reasonable standard, Kramer’s choice of location paid off. Breastfeeding rates were higher in the intervention group:
Rates of exclusive breastfeeding were lower than partial breastfeeding across the board, but again, much higher in the intervention group:
So how have the intervention children fared compared to the controls?
During their first 12 months of life, intervention infants had significantly fewer severe gastrointestinal infections and eczema, but not fewer ear or respiratory infections:
At age six and a half, the children from the intervention (largely breastfed) group had…
- No reduction in allergies and asthma. If anything, children who were breastfed showed a nonsignficant trends towards higher rates of allergies and asthma.
- No reduction in BMI or rates of obesity
- No difference in blood pressure
- No reduction in problem behaviors or attention disorders
- Higher IQ: +7.5 (+0.8 to +14.3) for verbal IQ, +2.9 (−3.3 to +9.1) for performance IQ, and +5.9 (−1.0 to +12.8) for full-scale IQ. (But no difference in IQ between infants exclusively breastfed for 3 months versus infants exclusively breastfed for 6 months.)
- Higher teacher ratings for reading and writing.
At age eleven and a half, the adolescents from the intervention group had…
- Lower rates of disordered eating among both girls and boys
- No reduction in BMI or body fat
- No difference in IGF-I (Insulin-Like Growth Factor–an important hormone for regulating growth and body composition.)
(Unfortunately, researchers did not re-assess the outcomes from age 6–academic performance, allergies, or asthma. Instead, researchers focused exclusively on weight and markers of metabolic health. So we cannot say whether the advantage in test scores among the intervention group persisted into adolescence. )
Summing Up the PROBIT Trial Findings To Date
The PROBIT trial suggests that breastfeeding does reduce the risk of severe gastrointestinal (GI) illness and eczema in the first year of life. The reduction in GI infections is supported by mountains of observational evidence, and this makes sound biological sense. Breastmilk contains numerous hormonal, immunological, and antimicrobial factors that aid gut maturation, help seed the growth of beneficial gut bacteria, and protect the gut from invading pathogens. However, the lower risk of infections lasts only until weaning. There is no clear long-term benefit.
What’s far more surprising, to my mind, is the apparent advantage in IQ seen at 6.5 years. The boost for intervention children was apparent in verbal, performance and overall IQ, as well as in teacher ratings of reading and writing.
The IQ and performance findings strike me as fairly compelling for a few reasons. (I can already envision a tidal wave of criticism coming at me for this statement. But please hear me out.)
First, if anything, the PROBIT trial errs on the side of understating the benefits of breastfeeding. This is because it is not randomized trial of breastfeeding, it is a randomized trial of a breastfeeding intervention. Some women in the control group breastfed their babies. Some women in the intervention group did not breastfeed their babies. This waters down the the differences between the control and intervention groups. If anything, the PROBIT trial is biased towards missing small benefits of breastfeeding.
Second, a benefit to brain development is biologically plausible. Breastmilk contains long- chain fatty acids, known to be important for retinal and neural development, as well as lactoferrin, a protein which binds to iron and may help protect the brain from iron-induced oxidative damage. Moreover, consistent with a true biological link, a large observational study demonstrated a dose-response relationship between duration of breastfeeding and childhood IQ at age 3 and age 7. The longer the children were breastfed, the higher their IQ, even controlling for maternal intelligence.
Third, one large sibling study also shows a small benefit in verbal ability among children who were breastfed, a finding which meshes well with those of the PROBIT trial.
Sibling Comparison Studies
In a sibling study, researchers compare the outcomes of siblings who were fed differently in infancy. In some cases, one sibling was breastfed while the other was not; in others, the siblings were breastfed for different lengths of time.
This allows researchers to largely avoid the problem of breastfeeding being confounded by race, socioeconomic status, maternal education, and so on.
(Of course, a family’s socioeconomic status and home environment can change from one birth to the next, but such differences between siblings are expected to be pretty minor, on average, compared to differences between families.)
If nothing else, sibling studies show how profoundly biased the observational studies are when it comes to studying breastfeeding.
The clearest illustration comes from a study of 1,773 siblings aged 4-14, led by Cynthia Colen of Ohio State University. Dr. Colen first analyzed her data as if it were from a typical observational study, comparing siblings across families. She found the usual result: Children who had been breastfed appeared to have significantly lower rates of obesity, asthma, and hyperactivity, and higher parental attachment, behavioral compliance, vocabulary, reading recognition, math ability, intelligence, and scholastic competence.
But then, she reanalyzed the same data, this time comparing siblings within families, thereby eliminating confounding by social and economic factors. And Voilà. She no longer found any apparent benefits of having been breastfed. In fact, the one remaining statistically significant effect was a higher risk of asthma among children who had been breastfed.
Another large sibling study has shown the exact same phenomenon: the apparent benefits of being breastfed vanished when the researchers compared siblings within families.
Other sibling studies find…
- Mixed results for IQ/cognitive ability:
- No difference in achievement test scores among 332 sibling pairs who differed in type of feeding, or among 545 sibling pairs who differed in how long they were breastfed.
- Higher vocabulary test scores among 2,734 adolescents who were breastfed compared to siblings who were not breastfed, but no benefits for GPA, likelihood to be held back a year, or likelihood of attending college.
- And mostly no benefit for BMI:
- Reduced BMI of 0.39 units (a differences of roughly 13-14 lbs. for a 14-year-old of average height) among one study of 118 adolescent sibling pairs.
- But no BMI benefit was seen in three larger studies, one of 267 adolescent sibling pairs, one of 1,773 children between the ages of 4 and 14, and one of 850 adolescent sibling pairs. Most notably, all three studies found a benefit when comparing across families. This benefit was no longer significant when comparing siblings within families.
The Bottom Line
The alleged long-term benefits of breastfeeding derive mainly from low- quality observational evidence. Better designed, less biased studies consistently fail to find these benefits.
Breastfeeding does appear lower the risk of gastrointestinal infections and eczema during infancy. For some–babies living in a developing nation, babies who are born very prematurely–the reduction in infections can be lifesaving.
Some limited evidence also suggests that breastfeeding may boost cognitive ability, especially verbal ability. But this boost, if real, is probably small. It’s way better to have a smart and loving mama than it is to be breastfed.
So why does the medical establishment rely on flimsy evidence to overstate the benefits of breastfeeding? To me, these poorly-supported claims feel downright condescending.
Instead of giving women the real pros and cons of breastfeeding and letting them make an informed decision about how to feed their baby, major medical organizations have made the decision for them, and then feel justified exaggerating and even fabricating the benefits to steer women towards making the “right” choice.
Worse, such claims do little to help our children. If we as a society truly want to raise children’s IQs, improve behavior, and reduce obesity, our efforts would be better spent addressing systemic problems–providing living wages, paid maternity and paternity leave, and affordable, high- quality childcare–than urging all women to breastfeed.
This is why I see the so-called “breastfeeding wars” as nothing more than a media-driven sideshow, an occasionally entertaining distraction from the real underlying problem: a lack of basic support for parents and other caregivers in our society.
Additional Reading
Like this post? Check out some related posts on how formula-fed babies tend to sleep longer at night, and why exclusive breastfeeding for 6 months is overrated.
References
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There’s some debate about the IQ findings in the PROBIT trial. I am moving the relevant points from a Facebook discussion here for all readers.
Here’s what Emily Oster, the author of Expecting Better, had to say about the PROBIT IQ results. (Note that she misstates several of the actual findings in this summary.) “First, researchers looked at all the kids in the study. For this sample, the evaluation of IQ was done by evaluators who knew whether or not a child was in the breastfeeding-encouraged treatment group. There were no significant effects of breastfeeding on overall IQ. In addition, breastfeeding had no effect on teachers’ evaluation of the children’s school performance. But the researchers observed large effects of breastfeeding on verbal IQ.
Because the researchers were concerned about evaluator bias, they also had a subset of children evaluated by independent evaluators who did not know which children were breastfed. The differences in verbal IQ disappeared. This, in combination with the teacher evaluations, makes it seem likely that the overall effect was driven by the evaluators, not by true differences among children because of breastfeeding” http://fivethirtyeight.com/…/everybody-calm-down-about…/
Here are some more details on this:
Oster is incorrect that there was only a benefit seen for verbal IQ. In fact, there were also significant differences found for in teacher ratings for writing and reading and for overall IQ.
But Oster is right that the testers were not blind to intervention status, which is a really bad design. The testers could easily have been biased towards “seeing” higher IQs in breastfed children.
To attempt to handle this, the researchers had a subset of the children retested by blinded “auditors”. All the same effects were seen, but were smaller in size.
From the original publication: “the auditors also rated children in the experimental group higher than those in the control group on all of the WASI tests and subtests. All of the differences favored the experimental group. The crude individual-based means for the experimental group vs the control group were 51.7 vs 50.6, respectively, for vocabulary, 54.2 vs 51.2, respectively, for similarities, 55.9 vs 53.7, respectively, for block designs, and 50.2 vs 48.9, respectively, for matrices, with means of 105.2 vs 102.1, respectively, for verbal IQ, 105.2 vs 102.6, respectively, for performance IQ, and 105.7 vs 102.6, respectively, for full-scale IQ. After accounting for the clustered randomization, the differences in means were of smaller magnitude than those seen in the test results from the pediatricians (mean differences [95% CIs], +2.8 [−3.2 to +8.8] for verbal IQ, +2.9 [−3.1 to +8.9] for performance IQ, and +3.1 [−2.9 to +9.2] for full-scale IQ).”
I was looking at your blog (I’m doing some research for a dissertation) and was looking at your information on breastfeeding. I think you should look more carefully at the studies you wish to reference. I’ve found many breastfeeding studies tend to compare breastfed (lumping both breastfed and mixed-fed) to exclusively formula-fed. Which I find bizarre. Imagine if you did a similar study on fat or salt a compared to independent groups similarly? – where perhaps low-salt was classed as having low salt intake everyday or just 1 day a month, and then compared it to a high-salt group? I cannot think of anything more biased.
‘‘Voldemort’ and health professional knowledge of risks of not breastfeeding?’ is an interesting read, which highlights the hypocrisy of research for breastfeeding.
Thanks for your feedback.
You raise a good question about how breastfeeding is measured, and whether different studies have looked at the amount of breastfeeding, instead of whether any breastfeeding occurred. Ultimately this is an issue of statistical power–studies that label short durations of breastfeeding as “breastfeeding” may water down the differences between formula-fed and breastfed infants, and therefore understate the true benefits of breastfeeding.
Failure to assess the amount of breastfeeding is a real problem for these studies, but it is unlikely to be the reason why sibling comparison studies and the one randomized controlled trial (which actually very carefully tracked duration of breastfeeding) failed to find the benefits observed in epidemiological studies.
The sibling studies and the RCT had large samples and were carefully designed. They may have overlooked small benefits–but that is kind of the point. Large benefits should have still been seen, provided they were in fact due to breastfeeding, and not some confounding factor like economic status or home stability or maternal intelligence.
So, to my mind, here’s the problem: The medical establishment dramatically overstate the long-term benefits of breastfeeding. Certainly, we do not tell women that there may be some slight long-term benefits of breastfeeding. We are not really sure, and the best-designed trials have failed to find them.
This talks about methodology. http://researchtheheadlines.org/2014/03/05/is-breast-truly-best-the-media-use-a-study-to-reject-decades-of-research/
I’m so glad that I’ve read this. I breastfed for 14 months, but hated nearly every minute of it. My daughter struggled to feed (and never got a good latch). I felt that it was the best thing to do for my daughter to carry on regardless and was terrified of the damage I would do to her if I stopped. I feel fairly convinced that it had a large impact on me ending up with PND. I barely slept for the the first year as my daughter fed round the clock. I would love to have another baby but have felt concerned over whether I would breastfeed again. After reading this I feel more confident that if I start to breastfeed and it’s not going well that I shouldn’t feel bad to give up. A happy Mum is worth much more than an unhappy breastfeeding Mum.
The only thing that isn’t mentioned in these studies is that breastfeeding reduces the risk of SIDS. This is one thing that the NHS really pushes and one of the main reasons I carried on. Did you come across any research about that?
Breastfeeding does not decrease SIDS. It’s not a causation but rather an association. Mothers who go out of their way to breastfeed are also more likely to follow the recommendations for not placing their infants in situations where they are more likely to get smothered while sleeping. SIDS is a term they created as a catch all for babies getting smothered in various ways – either because parent falls asleep and baby moves into a position where they can’t breathe or because they are placed in an unsafe sleeping environment to begin with/cosleeping/blankets in crib etc. There’s no known pathophysiology by which an infant just stops breathing without an explanation. It’s also why placing babies on their back without anything in the crib magically decreases SIDS aka being smothered.
For God’s sake, woman, if you want to nutritionally-deficient processed powder into your baby’s mouth, let your children cry themselves to sleep while you paint your nails, feed them McDonald’s ad pop them in front of the television while you create an entire blog to justify your laziness and slothfulness as a parent, just do it. I’m sure you’ll find a audience of women who had googled “Breastfeeding isn’t all that great” several hundred times in the google search field, and will love to find this “Well it looks smart” blog post that will make them feel better about their decisions to stop. However, overanalyzing 20-30 online abstracts, and clinging onto a few critiques on a handful of studies among the literal 100s of studies done supporting breastmilk over formula feeding, looks like grasping for straws here. No one has ever claimed that breastfeeding makes children more intelligent. That has been debunked, years ago. Its simply that children of breastfeeding mothers usually come from higher socio-economics and thus preform better academically. And yes, not every single study on any subject matter will be 100% methodologically perfect. No one has claimed this.
As far as this pretentious over-the-top blog post, not only are you going against empirical research, you’re going against the sound stance and advice of every western health institution and organization known to date. Any rational and “smart” thinking parent would take the advice of expert nutritionists, doctors and OBs over someone with a blog post and a unsupported opinion.
If you know of randomized trials or other sibling studies that avoid the problem of breastfeeding being confounded with education, wealth, employment, and home environment and *find* those purported benefits, I would love to see them.
One commonly cited benefit is the decreased rate of breast cancer to the mother. Did you find any information about whether this is true? For women with a family history of breast cancer, a benefit to her may be just as important as a benefit to her baby. Additionally, besides health benefits, I believe breastfeeding aids in bonding between the mother and the child. I’m not sure how you would study this, but that is as important to me as perceived health benefits.
Thanks for publishing this article. We have a week old baby girl who is breastfeeding and so far that is going very well. We intend to continue for as long as possible. All through the pregnancy we have been encouraged by health care professionals from the NHS and NCT to breastfeed. But none have been able to cite any actual studies when challenged. Many couldn’t suggest any of the proposed benefits. The posters in the hospital were the first source of information for the benefits. But they were unicef posters which I’d assumed would consider the benefits from an international perspective. The information needs to be more medicalised for everyone to make informed decisions.
Thanks this is a really useful article. I had realised that it must be highly confounded but didn’t have time to do the research. I had my IQ tests several times as a child and at uni. I did a bit of research into it and it is very difficult to measure. The increases observed in small studies will be difficult to draw conclusions from because of the large confidence intervals in the scores.