New Lancet paper does NOT show that breastfeeding reduces post-neonatal mortality

There’s a new study in The Lancet that claims to show that breastfeeding saves lives.

According to Breastfeeding and Post-perinatal Infant Deaths in the United States, A National Prospective Cohort Analysis:

Breastfeeding initiation is significantly associated with reduced odds of post-perinatal infant deaths in multiple racial and ethnic groups within the US population. These findings support efforts to improve breastfeeding in infant mortality reduction initiatives.

No, the study supports nothing of the kind. It’s no different than doing a study that shows that Volvo ownership is significantly associated with reduced odds of post-perinatal infant deaths and concluding that we need to improve access to Volvos for all families.

The problem with studies like this — and there are many studies like this — is that breastfeeding is socially patterned. Women who breastfeed differ in substantial and meaningful ways from women who don’t breastfeed. Families of women who breastfeed differ in substantial and meaningful ways from families where of women who don’t breastfeed. And it is those substantial differences that account for the differences in post-neonatal mortality rates.

There are three major limitations to the study:

1. Correlation is not causation. Yes, breastfeeding is CORRELATED with reduced post-perinatal mortality, but the study provides NO evidence that breastfeeding CAUSES reduced post-perinatal mortality.

2. There was no dose response relationship since the authors only compared ever breastfed to never breastfed. In other words, the primary difference between the two cohorts is mother’s intention not the amount of breastmilk received.

3. As mentioned above, breastfeeding is socially patterned. Breastfeeding is associated with lower rates of post-perinatal death for the same reason Volvos are associated with lower rates of post-perinatal death. Both are proxies for a host of social and economic factors.

It is true that the authors tried to correct for some of these variables but the corrections are imperfect. For example, they did not correct for maternal socio-economic status though they did correct for things like maternal education and insurance status that are related to socio-economic status.

The authors acknowledge these limitations:

An important limitation of our analysis is the lack of data regarding duration and exclusivity of breastfeeding from birth certificates… [U]sing the vital statistic data alone, this study could not identify the causal pathway between initiating breastfeeding and infant mortality, such as structural racism and other social determinants of health that impact breastfeeding practices and infant outcomes especially among Black women… Despite our statistical efforts towards a more robust study design, we may not have completely ruled out the reverse causality and residual confounding effects given the nature of this study…”

Finally, the authors are NOT independent researchers looking to advance the state of knowledge. They’re part of a breastfeeding lobby looking to increase funding for their efforts.

Consider their conclusion:

…[W]e have identified significant associations between the initiation of any breastfeeding and reduced post-perinatal deaths in the US population, with consistent findings in various stratified analyses representing different demographics and health status. These findings support integrating efforts to promote, protect, and support breastfeeding for US infant mortality reduction efforts.

But the findings — as the authors themselves admit — did NOT demonstrate that breastfeeding reduces infant mortality so they don’t support ANYTHING and certainly not promotion of breastfeeding.

The sad fact is that the real cause of post-perinatal mortality is almost certainly financial and structural inequities, NOT breastfeeding, and focusing on breastfeeding just benefits the breastfeeding lobby without doing anything for babies.