Why does breastfeeding often fail?

Disappointment motherhood. Mother tired

Breastfeeding is not a matter of will; it is a matter of biology.

That’s the take home message from the paper Biological underpinnings of breastfeeding challenges: the role of genetics, diet, and environment on lactation physiology by Lee and Kelleher, graduate student and professor of cellular physiology respectively.

[pullquote align=”right” cite=”” link=”” color=”” class=”” size=””]To pretend that breastfeeding is just a matter of will and support is both empirically wrong and gratuitously cruel.[/pullquote]

The most pernicious of the many pernicious lies promoted by lactation consultants is that any woman who wants to breastfeed can do so successfully. That’s why when breastfeeding fails, lactivists insist that it is because the mother didn’t try hard enough or didn’t get enough support. But lactation is a biological process and like any biological process it has a significant failure rate. Those failures of biologically based.

As the authors of the paper explain:

It has long been assumed that once lactation is successfully initiated, the primary factor regulating milk production is infant demand. Thus, most interventions have focused on improving breastfeeding education and early lactation support. However, in addition to infant demand, increasing evidence from studies conducted in experimental animal models, production animals, and breastfeeding women suggests that a diverse array of maternal factors may also affect milk production and composition.


…[I]t has been estimated that the prevalence of women who overtly fail to produce enough milk may be as high as ∼10–15% and can quickly lead to hypernatremia, nutritional deficiencies, or failure to thrive. Moreover, the prevalence of lactation “insufficiency” may be much higher, as ∼40–50% of women in the US and 60–90% of women internationally cite “not producing enough milk” or “baby not satisfied with breast milk” as the primary reasons for weaning prior to 6 mo.

Why does this happen?

In this review, we provide a broad overview on our current understanding of the molecular etiology behind these factors that play a critical role in lactation physiology and the ability to optimally nourish the nursing infant.

Let’s pause here to address the inevitable lactivist claim that we “wouldn’t be here” if breastfeeding had a high failure rate.

To understand why the claim is false, it helps to analogize to miscarriages. Although the survival of the human race depends on successful pregnancies, it is entirely compatible with a natural miscarriage rate of 20%. There is a biological basis for those miscarriages; most are due to serious genetic defects present at conceptions, some are due to hormonal imbalances, and some are the result of factors we have not yet indentified. Furthermore, no amount of maternal effort or outside support can prevent miscarriages. A few can be prevented with medical interventions but most can’t be prevented at all. The same thing applies to insufficient breastmilk production.

Breastmilk production is a complex process:

During early pregnancy, primary hormones, including estrogen, progesterone, prolactin, and placental lactogen, induce the physiological transition of the mammary gland from a nonsecreting branched tissue into a highly active secreting organ comprised of a vast network of ducts and alveoli that are grouped into seven to 10 lobes in humans… In response to progesterone and estrogen withdrawal, concomitant with prolactin release following parturition, the differentiated epithelium gains a remarkable capacity to finely coordinate the synthesis and transport of various milk constituents for the onset of milk secretion, … which usually occurs after full-term birth in humans.

There are many ways that things can go wrong.

Breast hypoplasia or other abnormal breast conditions and previous breast surgeries are certainly factors that contribute to lactation insufficiency… What is much less appreciated and poorly understood is the role that maternal genetics and modifiable factors such as energy balance, diet, and environmental exposures may have on reproductive endocrinology, lactation physiology, and the ability to successfully breastfeed.


…[R]ecent advancements have identified numerous genetic variants associated with milk production traits in production animals. A recent study using GWAS data collected from 16,812 Holstein and Jersey dairy cattle identified SNPs in key pathways that are critical for mammary gland development, prolactin signaling, and involution that explained variation in milk production and milk composition. For example, ∼50% of SNPs found in genes critical for prolactin signaling, including SOCS2, STAT3, STAT5A, STAT5B, PRLR, and β-casein, were associated with three or more milk production traits. Additionally, a large number of SNPs in genes that are critical for mammary gland involution, including ATF4, IGFBP4, IRF1, LIFR, OSMR, PTK2, and STAT3, were also associated with milk production traits…

We propose that similar variation may govern lactation physiology, milk production, and composition in breastfeeding women…


In addition to prolactin, a complex combination of hormones works together to maintain the differentiated epithelium and milk secretion during lactation, including insulin, glucocorticoids, growth hormone, oxytocin, and thyroid hormone. Secretory activation and milk ejection require insulin and glucocorticoids to synergistically regulate the formation of tight junctions in the mammary gland, stimulate mammary differentiation, and induce milk protein expression. Insulin levels rapidly decrease during early lactation and steadily increase over time.


Growing evidence suggests that in addition to systemic inflammation, obesity is also associated with an inflammatory microenvironment in the mammary gland, which has recently been associated with premature involution in murine models… Fundamentally, the altered mammary gland microenvironment that occurs in obesity can lead to failed secretory activation or suboptimal lactation, whereby the mammary gland is incapable of secreting copious milk to nourish the newborn.


In recent years, increasing evidence shows not only that adequate nutrient intake and appropriate nutrient homeostasis are important for maintaining maternal energy balance but that suboptimal nutrition has significant effects on breast physiology and milk production, secretion, and composition. Nutrient deficiencies can result in failed secretory activation from several perspectives, such as inefficient hormone responsiveness, and defects in cellular processes involved in morphogenesis and secretory pathways. Moreover, energy/nutrient imbalance may cause more perverse effects on immune response and increased risk of mastitis…

Environmental factors

Thus far, only a few studies in women have shown an association between toxins like PCBs and dichlorodiphenyl dichloroethene and lactation defects such that exposure to these toxins is associated with shorter breastfeeding duration…

…[N]atural components such as heavy metals exposure can affect the mammary gland during lactation. Some heavy metals (copper, zinc, and manganese) are biologically essential; however, the most pollutant heavy metals are lead, cadmium, and mercury that bioaccumulate following absorption, causing adverse health effects.

The bottom line is that lactation insufficiency is common; it can be caused by non-modifiable factors like structural breast abnormalities, genetics, hormonal imbalances and environmental exposures. No amount of maternal effort and no amount of lactation support has any impact on those factors.

To pretend that breastfeeding is just a matter of will and support is both empirically wrong and gratuitously cruel.