By Alison Heyerdahl

It’s not a secret that breastfeeding and pumping are a challenge for most new mothers.  Some of the difficulties include getting the correct latch, not knowing whether your baby is getting enough milk with each feed, and worrying that your diet may be affecting your baby’s digestion (causing colic, asthma, or allergic reactions).  Many mothers also find that they are unable to pump enough breast milk to sustain a good supply.

Although the American Association of Pediatrics recommends that mothers exclusively breastfeed their babies for the first 6 months of life, up to 10 – 15% of mothers who intend to breastfeed fail to produce enough milk, leading to nutritional deficiencies and ‘failure to thrive’ in their infants.  This article aims to address what causes a low milk supply.

Factors causing a low milk supply

It has long been thought that after birth, a mother’s milk supply is solely dependent on the amount the infant drinks - a ‘supply and demand’ process.  In other words, each time milk is removed by the suckling infant, more is produced.  As a result, early interventions have focused mainly on breastfeeding support in the form of education for newly breastfeeding mothers.   However, in addition to infant demand, there are also an array of maternal factors that can lead to a decreased milk supply.  These include genetics and factors such as diet and environmental influences. 

Signs your baby isn’t getting enough milk

• Lack of weight gain is a common sign that baby is not getting enough milk.  Although babies can lose up to 10% of their weight, by the two weeks of age, they should be back to birth weight and gaining with 0.7 oz/day (minimum).

• Dehydration, indicated by the presence of dark urine (rather than the normal pale yellow color), a dry mouth, or a yellowish coloring of the skin or eyes may be a symptom of lack of milk supply.  

• Diaper counts are a critical indicator of the baby’s hydration status. The first week, baby’s diapers will increase by day/age. By the end of the first week of life, your infant should be having 6-8 wet diapers, and 3-4 yellow seedy stools in a 24 hour period. 

Genetic and Environmental Factors affecting milk supply

The breasts (or mammary glands) are extremely complex glands that produce, secrete, and deliver milk to the infant.  Interestingly, although the breasts develop their basic structure during puberty, most of the development occurs postnatally (or after birth).  The molecular, cellular, and biochemical processes that regulate the nutrient transport to the mammary glands, milk production, and milk secretion are largely determined by maternal hormones.  Oxytocin (the love or cuddle hormone) is mainly responsible for the milk ejection reflex.  It is activated by infant suckling and milk removal.  Low levels of maternal oxytocin can occur because of environmental factors such as stress, anxiety, depression, having pain (as in after a C-section), breast surgery (especially if it has involved cutting through the nipple area), fatigue, and illness, which affects milk production. 

Other diagnosis such as diabetes, hypothyroidism, hypertension, and PCOS also play into the amount of milk created. Maternal obesity is another factor that is strongly linked to low milk supply and early cessation of breastfeeding (due to higher insulin resistance).  Furthermore, a poor diet can have effects on breast physiology, milk production, and secretion.

Another reason for low milk supply may be the presence of a genetic mutation (specifically a mutation in the protein ZnT2, which is responsible for the transportation of zinc to the mammary glands).  According to one published study, this occurs in approximately 36% of women!  Zinc is necessary for the growth and function of the mammary glands, in addition to the secretion pathways.  A lack of zinc can lead to difficulty in breastfeeding and cause a low milk supply.  Even if these babies are successfully breastfed, the milk will contain much lower levels of zinc, leading to possible immunological and developmental issues.  

In conclusion, although it is recommended that infants are exclusively breastfed for the first 6 months of life, it should not be assumed that breastfeeding or expressing will be easy. Many mothers have difficulty breastfeeding or pumping due to genetic factors, diet, and environmental influences.