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…