More than 130m women give birth each year. Over 90% of women alive who have not yet given birth are expected to do so at some point. Around 90% of mothers in rich countries start breastfeeding; a quarter give up within a few weeks, often because they fear insufficient supply. Two in five who attempt breastfeeding encounter problems. A 2016 Lancet study estimated that universal breastfeeding could avert 823,000 deaths of under-fives each year, largely because in poor countries formula is often made with dirty water.
A search for "low milk supply" or "low milk production" returns about 14,000 papers on PubMed (a database of 40m). "Erectile dysfunction" elicits 32,000. Medicine has no dedicated specialism for the mammary gland—what would be called "lactology". In parts of Europe 20-40% of newborns are fed powdered milk before leaving hospital.
For years doctors assumed inadequate milk supply affected no more than 5% of mothers; recent research suggests 10-20%. Studies of breast milk now use samples as "liquid biopsies", relying on microRNA from breast cells (discovered in 2010).
Lactocytes—milk-secreting cells—multiply rapidly during pregnancy and begin secreting about three days after birth. Some lactocytes hoard multiple copies of their own DNA to produce more milk. Research by Lindsay Hinck at UC Santa Cruz, published in Nature Communications in 2024, found that low levels of the WEE1 enzyme disrupt a cell-repair mechanism, leading to fewer functioning lactocytes in mice. Rachel Walker at Penn State has linked placental damage and chronic inflammation to low supply. Pre-eclampsia, obesity, diabetes and autoimmune disorders can all reduce supply; up to half of women with such conditions develop low supply.
Other risk factors include certain zinc-transport gene mutations and "widely spaced" breasts (which often have little glandular tissue). Australian researchers showed in 2025 that hand-held probes can gauge sodium in breast milk, a useful indicator of malfunctioning lactocytes.
It's no longer a question of staying healthy. It's a question of finding a sickness you like.