The Evidence on Breastfeeding

In an article the Royal Statistical Society announced as the runner-up in their annual Awards for Statistical Excellence in Journalism, Helen Rumbelow thoroughly investigates the well-debated subject of breastfeeding.

The conclusion of the piece is that much of the evidence in support of breastfeeding is massively misrepresented or inherently flawed.

“The evidence to date suggests it probably doesn’t make much difference if you breastfeed.” […]

“The conclusion is that the evidence we have now is not compelling. It certainly does not justify the rhetoric,” [American academic Joan Wolf] says. The problem with the studies is that it is very hard to separate the benefits of the mother’s milk from the benefits of the kind of mother who chooses to breastfeed. In the UK, for example, the highest class of women are 60 per cent more likely to breastfeed than the lowest, so it is not surprising that research shows that breastfed infants display all the health and educational benefits they were born into. But even if education, class and wealth is taken into account, there is known to be a big difference between the type of mother who follows the advice of her doctor and breastfeeds, and the one that ignores it to give the bottle. In other words, breastfeeding studies could simply be showing what it’s like to grow up in a family that makes an effort to be healthy and responsible, as opposed to anything positive in breast milk.

This is not to say that breastfeeding is not good:

  • Wolf acknowledges that it helps prevent gastrointestinal infections (life-saving in the developing world, generally a mild complaint in the West).
  • Michael Kramer (one of the world’s most authoritative sources of breastfeeding research; advisor to the WHO, Unicef and the Cochrane Library) believes:
    • The evidence is “encouraging” in preventing respiratory problems.
    • The data on helping prevent breast cancer is “solid”.


  • The data on obesity, allergies, asthma, leukaemia, lymphoma, bowel disease, type 1 diabetes, heart disease and blood pressure are “weak” at best.
  • The “highly respected” American Agency for Healthcare Research and Quality (AHRQ) warns that, “because the breastfeeding mothers were self-selecting, ‘one should not infer causality’”.
  • The World Health Organisation’s own research review concluded that gains were “modest” and also warned that “because none of the studies it looked at dealt with the problem of confounding, the results could be explained by the ‘self-selection of breastfeeding mothers’”.

via @TimHarford