How genes may influence breast milk production

Breastfeeding is central to health and child survival. The Ministry of Health notes that about six in 10 infants under six months are exclusively breastfed.

This places Kenya above the global average of 48 per cent, as reported by UNICEF. Despite this progress, many mothers still stop breastfeeding earlier than planned because they feel they are not producing enough milk, leading to early supplementation or weaning.

Recent research published in the journal Science Advances provides fresh insight into understanding why some women struggle to produce milk.

Scientists at the University of California, San Francisco (UCSF) examined breast milk samples from 30 lactating women, dividing them into three groups of low, normal and high milk producers.

By applying advanced techniques such as single cell sequencing, the researchers were able to look at differences in genes and cell types between these groups. Their work revealed that certain genes appear to influence how much milk a mother produces.

The researchers identified three genes of particular interest. One called PLIN4 (a gene that helps regulate how fat is stored in the body) was found at higher levels in women with low milk supply. Another, GLP1R (a gene linked to hormone signalling that affects how the body uses energy), was also associated with low supply. In contrast, KLF10 (a gene that influences how cells grow and respond to signals) was more prominent among those whose milk supply was higher.

They also discovered that the balance of different cell types in breast milk varied across the groups. One type of breast cell, known as epithelial cells (cells that line the milk ducts and help secrete milk), showed notable differences. A particular subtype called LC2 C was more common in mothers with normal milk production than in those with either low or high supply. The scientists further observed that the amount of fat in milk was linked to the proportion of these LC2 C cells.

What makes the findings especially relevant is that even where mothers had low production, the infants did not show reduced diversity in their gut microbiome compared to babies whose mothers had normal supply. This suggests that partial breastfeeding still provides meaningful health benefits, particularly in establishing immunity and gut health.

The research team noted that many of the mothers in the low supply group had experienced delays in mill production after birth, a condition known as delayed lactogenesis, which further points to the biological underpinnings of milk production.

These discoveries carry weight in Kenya, where the perception of insufficient milk is one of the most common reasons women give for introducing formula or other foods earlier than recommended. The World Health Organization (WHO) has emphasised that early initiation of breastfeeding within the first hour of life and exclusive breastfeeding for the first six months are essential steps in improving child survival.

Kenya has made significant strides in this regard. Exclusive breastfeeding rates have climbed from only 13 per cent in 1998 to 60 per cent in 2022, while more mothers are now beginning to breastfeed shortly after delivery. Rwanda currently leads in the region with exclusive breastfeeding at more than 80 per cent, while in countries such as Gabon the rate remains below 20 per cent, according to a recent multi-country study published in BMC Pregnancy and Childbirth.

Understanding the genetic aspects of lactation does not mean that genes alone determine supply. Nutrition, maternal health, stress levels, workload and support from health systems all play a role.

According to UNICEF, supportive policies, including workplace accommodation for breastfeeding and enforcement of maternity leave, are essential in enabling mothers to sustain exclusive breastfeeding. Nutritionists also point out that well-balanced diets rich in micronutrients help mothers maintain milk production.

Tailored support

The UCSF study was based on a relatively small group of participants, so local studies are needed to determine whether the same genes and cellular processes influence milk supply among Kenyan women, given differences in genetic background, diet and environmental conditions.

Identifying genetic markers of low supply could help health professionals offer more tailored support, from closer monitoring in maternity wards to early referral for lactation counselling. Community health workers could be better trained to distinguish between mothers experiencing true biological insufficiency and those whose challenges stem from modifiable factors such as poor latch or lack of support.

Kenya has achieved much in raising breastfeeding rates, but sustaining these gains requires investment in maternal support, nutrition programmes and local research.

Professor Valerie Flaherman, one of the researchers involved in the UCSF study, explained, these discoveries are an important step towards understanding why some mothers struggle with supply.