May 12th 2026|7 min read
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THE STRUGGLE to breastfeed is a defining feature of early motherhood for many women. Of the approximately 90% of mothers in rich countries who start breastfeeding, a quarter give up within a few weeks, often because they fear they are not producing enough milk to feed their babies. For many years doctors have assumed that true cases of poor supply are rare, occurring in no more than 5% of mothers. The prevailing advice to worried parents from health authorities in places such as England and America has, therefore, been to stimulate the release of milk by either putting the baby to the breast more often or using a breastpump.
This advice, though well-meaning, is turning out to be inadequate. Many women who follow it still end up with babies who fail to gain enough weight—a clear sign that the mothers are not producing enough milk. Studies of breast-milk production involving hundreds of women in America and Australia in recent years suggest that the proportion of mothers who produce too little milk is far higher than previously thought: between 10% and 20%.
Researchers are beginning to understand why these numbers are so elevated. For many women, the explanation lies not in how they breastfeed but in the composition and function of unique cells in the mammary gland, an aspect of their biology over which they have no control. Further research may one day lead to treatments. But even in the short term these discoveries should help destigmatise low milk supply. “In the last ten years it has become more [accepted] that there is a biological reason for these cases,” says Yarden Golan Maor, who studies human milk production at Cornell University. “And it’s not, you know, you’re just not trying hard enough.”
At the heart of the matter are lactocytes, cells in the mammary glands that multiply rapidly during pregnancy and begin to secrete breast milk about three days after a woman gives birth. In the past, obtaining such cells for study would have required a tissue biopsy from a breastfeeding woman. That made research into lactation biology tricky. In 2010, however, researchers discovered that microRNA molecules from the mother’s breast cells (which contain information about those cells’ function) were abundant in breast milk. Breast milk samples could, therefore, be used as liquid biopsies to understand the causes of low milk production.
Such work has revealed distinct biological pathways for what is going wrong. Some women have too few lactocytes. Others may have lactocytes that are inefficient and secrete little breast milk.
Lindsay Hinck at the University of California in Santa Cruz has made progress on untangling the first of those issues. The problem may begin in pregnancy, when individual lactocytes repeatedly divide to form pairs of daughter cells identical to their mothers. Some lactocytes, however, are different: instead of giving rise to new cells, they hoard multiple copies of their own DNA within themselves, a trick that allows them to make more milk.
Both populations of cells are at risk of accumulating random DNA mutations, which can cause them to either die or stop working. And although a cell-repair mechanism exists which can boost the numbers of the hoarding cells, it does not always work as planned. In experiments conducted in mice, reported in Nature Communications in 2024, Dr Hinck’s team found that low levels of an enzyme called WEE1 disrupts this repair mechanism, leading to fewer functioning lactocytes and low milk supply. A deficiency of WEE1 could be responsible for low lactocyte levels in humans, too, says Dr Hinck.
Rachel Walker at Penn State University is testing a hypothesis regarding what may be a separate mechanism. Many of the hormones that instruct the lactocytes to multiply and prepare the mammary gland for lactation are made in the placenta. As some animal studies have tentatively linked damage to the placenta with low milk production, Dr Walker and her team are examining whether this could be the case in humans, too. They are studying the placentas of new mothers in Uganda to see whether infection, among other things, is connected to low milk supply. If such a link is found, it might eventually be possible to predict the likelihood of low milk supply at the moment of childbirth.
Progress has also been made on understanding why lactocytes might not function efficiently. One possible cause is a deficiency of critical nutrients in the mammary gland. These provide energy for the lactocytes’ normal functioning and are used as ingredients in the breast milk that they secrete. Researchers believe that a shortage would cause the lactocytes to either work harder to make up the shortage or else lose energy. Both scenarios might cause them to make less milk.
Such shortages are not necessarily the product of the mother’s diet; certain gene variants and inflammatory molecules can also play a part. Some women, for example, have a gene mutation that affects how zinc passes from the blood into breast milk. Zinc is not only an important nutrient for babies, but is also involved in the development of the mammary gland. Researchers have found that having this mutation is linked with low milk supply.
Large-scale genomic studies in cows have also found genes that regulate the protein content of milk, some versions of which may also exist in humans. Women with these genes may struggle to have the right nutrient balance to trigger their lactocytes. That being said, scientists think that genetic causes of low milk supply are probably rare, as the associated mutations are unlikely to have been favoured by natural selection. Genetics, in other words, cannot be the end of the story.
Another prime suspect seems to be inflammation. In 2022 Dr Walker and her colleagues published research showing that chronic inflammation (the type common in obesity and auto-immune disorders like diabetes) prevents fatty acids in the blood from entering the mammary glands and enriching the breast milk. Specific inflammatory molecules can also disrupt the synthesis of carbohydrates, another important component of breast milk.
This growing body of research highlights a number of factors that may increase a woman’s risk of having low supply. Obesity, diabetes and autoimmune disorders, for example, lead to chronic inflammation which can disturb the functioning of many organs in the body. Pre-eclampsia, a disease of the placenta that affects roughly 4% of women, can also damage many organs. For women with some of these conditions, studies show that up to half may end up with low milk supply.
Other causes are less clear. One risk factor that a number of studies have identified is having breasts that are more widely spaced than average. Women who fall into this category often have little glandular tissue and, therefore, fewer lactocytes. Some research suggests obesity in early life may play a role, affecting the mammary gland’s ability to grow at this crucial period of its development. But at the moment, says Dr Golan Maor, “It’s all speculation.” There is clearly much more research to be done.
Untangling the biology of lactation could have dramatic benefits for new mothers. Most straightforwardly, tests to diagnose low milk production would open the door to more tailored advice as well as potential treatments.
Some such tests are already being developed. In a paper from 2025 a team of Australian researchers showed that hand-held probes can accurately gauge sodium levels in breast milk, a useful indicator of malfunctioning lactocytes (as well as other conditions such as mastitis). When milk secretion begins, the spaces between the cells lining the mammary gland normally close up, preventing sodium from leaking into breast milk. Abnormally high sodium levels in a mother with suspected low milk supply would suggest some underlying biological issue.
More such innovations will hopefully hit the market soon. If lactation science continues in this way, millions of women who suspect they are making too little milk could get timely and definitive answers on whether that is, indeed, the case. ■
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This article appeared in the Science & technology section of the print edition under the headline “Feeling low”
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