Breastfeeding: Breast Milk: More Than Nutrition – How It Supports Infant Development

From immune protection and gut health to biological signalling, discover why breast milk is one of nature's most remarkable early-life foods.

Each year, World Breastfeeding Week celebrates and supports breastfeeding mothers whilst raising awareness of the remarkable role breast milk plays in early life. August marks this global campaign coordinated by the World Alliance for Breastfeeding Action (WABA) and supported by the World Health Organisation (WHO) and the United Nations children’s fund (UNICEF). 

Long before the development of our modern infant formulas, breastfeeding was the only way for a newborn to receive the nutrition needed for growth and survival. In some wealthy societies, where breastfeeding was often viewed as too common, or inconvenient, families often employed a ‘wet nurse’ to breastfeed and care for their baby.  

Throughout history, breast milk has been central to infant nourishment and remains the biological norm in which infant nutrition is measured. Today (thankfully) we have an array of highly nutritious infant formulas that provide a valuable and convenient alternative to breastfeeding when breastfeeding is not possible or practical.  

However, research continues to show that breast milk does more than simply feed a baby. It nourishes, protects, communicates and helps programme many aspects of early development, delivering not only nutrients, but also immune factors, beneficial bacteria, hormone and biological signals that support growth, health and development.

A Living Fluid That Changes with Your Baby 

Unlike formula, breast milk is not static. Its composition changes day by day, and even within a single feed, to match the developmental stage and requirements of the infant. It provides a balance of proteins, fats, carbohydrates, enzymes vitamins, minerals, hormones, growth factors and immune compounds that work together to support growth and development.  

This perfect balance of nutrition is tailored by nature for a baby’s evolving needs. During the first 3-5 days after birth, the first milk is known as colostrum, often referred to as ‘liquid gold’. This thick, yellowish fluid is exceptionally rich in antibodies, immune cells and growth factors that help protect the newborn against infection whilst supporting the development of the gastrointestinal tract and immune system. 

The yellow colour of colostrum comes largely from carotenoids and vitamin A. Importantly, this first milk delivers high concentrations of secretory Immunoglobulin A (sIgA), a specialised antibody that helps to form a protective barrier along the babies intestinal lining that helps to protect against bacteria, viruses, and other pathogens whilst their own immune system matures. 

Tiring as it is for mothers, the frequent feeding during these first few days stimulates ongoing milk production and supports the transition to the next phase of lactation. 

Following colostrum production, what is known as transitional milk develops between days 6 to 15. This is often what mothers refer to when they say, ‘my milk has come in’. transitional milk is produced in larger volumes and contains more fat, calories and lactose to support the rapid growth and healthy weight gain.  

By around two weeks postpartum, mature milk becomes established. Mature milk provides a carefully balanced mix of fats, proteins, carbohydrates, enzymes, hormones and immune compounds that continues to adapt to the baby’s changing needs, including the very important hydration needs. 

Systemic reviews have demonstrated that breastfeeding, with its hundreds to thousands of bioactive molecules, helps protect against infection and inflammation whilst supporting immune maturation, organ development and gut health. For mothers, breastfeeding has also been associated with long-term health benefits, including a reduced risk of breast and ovarian cancer, osteoporosis, obesity and cardiovascular disease.  

How Breastfeeding Helps Seed a Baby’s Gut 

Recent research suggests that breast milk helps ‘seed’ the infant gut with beneficial bacteria from the mother. Human milk contains its own microbiome, and studies show that some of these microbes can be transferred directly into the baby’s gastrointestinal tract during feeding. Interestingly, the effect appears to be dose-dependent, meaning that greater the exposure to breast milk is associated with greater microbial transfer. These early microbial settlers help establish the infant gut ecosystem, influencing immune development, digestion and long-term health.  

Alongside this internal route, beneficial microbes may also be transferred through skin-to-skin contact and through interactions between the baby’s mouth and the breast during feeding. 

Together these pathways demonstrate that breast milk is not sterile, instead it contains a community of beneficial microorganisms 

Supporting Mum Supports Baby 

The recommendations encourage exclusive breastfeeding for the first six months of life where possible, however, it is not always straightforward. 

Many mums experience challenges such as – 

• Low milk supply 
• Latching and feeding difficulties 
• Fatigue 
• Breast pain 
• Returning to work 
• Feeling self-conscious about feeding in public (or even with the family around) 
• Stress and overwhelm 
• Postnatal depression 

Thankfully we now have more support, education and practical guidance for new (and experienced) mothers that can make a significant difference navigating these challenges. 

Milk production is nutritionally demanding and if breast milk is to be the baby’s only source of nutrition during the first six months, mums must provide those nutrients for milk production whilst continuously replacing nutrients lost from their own stores. 

The body will often prioritise the nutritional needs of the infant, meaning mothers can become depleted if their own nutrient intake is poor or inadequate. 

Nutrients That Support Healthy Milk Production

Nursing mothers need adequate protein to help form many of the structural and functional components of breast milk as well as healthy fats, and adequate levels of carbohydrates to meet the increased energy demands associated with breast milk production. 

Some key nutrients are worth a mention such as - 

• B vitamins 
• Vitamin A 
• Vitamin D 
• Iodine 
• Choline 
• Omega-3 fatty acids, particularly DHA 

B vitamins are involved in cellular energy production and metabolism. Producing breast milk requires significant energy, and adequate levels of B vitamins helps support the metabolic processes involved in milk synthesises. B vitamins are transferred into the breast milk, maintaining good maternal status also helps ensure a consistent supply for the growing infant. 

Vitamin A contributes to the maintenance of healthy epithelial lining of the milk ducts to ensure healthy milk secretion. Adequate vitamin A levels in breast milk are also important for the baby, as it plays a key role in vision, immune development, and the growth and development of organs and tissues during early life. 

Vitamin D levels in breast milk are closely linked to a mothers Vitamin D status. Maintaining adequate vitamin D levels through sunlight exposure, diet and supplementation where appropriate, helps support maternal health throughout lactation (the NHS recommends at least 400iu for mum during breastfeeding) Maternal status also influences how much vitamin D is available to the baby via the breastmilk. 

Iodine requirements increase during breastfeeding as iodine is actively transported into breast milk. Adequate intake is therefore important to maintain maternal thyroid hormone production and support the body’s increased physiological demands during lactation. It also helps ensure sufficient iodine is available in breast milk to support healthy growth and development. 

Omega-3 fatty acids influence the fatty acid composition of breast milk as well as mother’s requirements that remain high during breastfeeding. As these fats are transferred into breast milk, mothers with low dietary intake may gradually deplete their own stores. Therefore, eating oily fish and/or supplementing the diet would give mum and baby the best support. However, research suggests that a mother’s long-term diet influenced the omega-3 content of her breast milk rather than what she ate over the previous few days. Therefore, regular intake of oily fish or plant and marine sources of omega-3 helps are required to build the maternal stores that are then reflected in breast milk 

Ensuring adequate intake of omega-3 fats helps support healthy brain development, visual development and retinal function as well as the formation of cell membranes throughout the nervous system of the growing baby. 

Choline deserves a special mention as it is one of the most concentrated nutrients transferred into breast milk, meaning a mothers requirements increase significantly during breastfeeding.  

Choline is essential for infant brain development and is involved in the production of cell membranes, nerve signalling and normal liver function. It also plays an important role during lactation, a period of high metabolic demand. 

Whilst the body can produce small amounts, choline is considered an essential nutrient because we cannot make enough to meet our needs so we must take it from our food such as eggs, red meat, chicken, turkey, legumes such as soybeans, kidney beans, cruciferous vegetables and shitake mushrooms. 

Whilst not technically a mineral or a vitamin, it is often found grouped together with B vitamin complex in a supplement as they work closely together as methyl donors, supporting our methylation cycle that is required for thousands of essential reactions throughout the body. Mum’s who are depleted in this nutrient may need to supplement their diet, especially when breastfeeding.  

One supplement that has shown very beneficial is Lecithin which is a naturally occurring mixture of phospholipids, the most important of which is phosphatidylcholine which is a major source of choline that is attached to the phospholipid. Lecithin is found in soybeans, sunflower seeds and egg yolks.  

Lecithin for Healthy Milk Flow

Breastmilk is a complex emulsion of fats and water, lecithin acts as an emulsifier, helping to keep milk fats evenly dispersed rather than clumping together. Whilst it does not increase milk volume there is much anecdotal and observational reports that it may help to reduce the thickness or stickiness of breast milk, helping it to flow more freely through the milk ducts and lowering the risk of recurrent blocked ducts in susceptible women which is a major reason many mothers give up on breast feeding.  

Breast Milk as Chrononutrition

Perhaps one of the most remarkable discoveries is that breast milk changes according to the time of day it is produced. 

Emerging research suggests breast milk acts as a form of chrononutrition, delivering biological signals that may help regulate an infant’s developing circadian rhythm which baby formulas cannot provide.  

Night-time milk contains higher levels of melatonin and tryptophan; compounds associated with sleep and relaxation. Daytime milk contains higher levels of cortisol; a hormone linked with wakefulness and alertness. 

Scientists believe these natural fluctuations may help teach infants about day and night before their own circadian rhythms become fully established. 

In many ways, breast milk can be viewed as a sophisticated communication system between mother and baby, helping to regulate sleep, metabolism, immune development and growth. 

Final Thoughts

While breastfeeding is widely recognised as the gold standard for infant feeding, it is important to acknowledge that every feeding journey is different. For mums who can breastfeed, supporting their own nutrition and lifestyle is fundamental, as maternal nutrient status influences both maternal wellbeing and the nourishment provided to their baby. 

World breastfeeding week serves as a reminder that breast milk is one of nature’s most remarkable biological systems. From supporting immune function and helping seed the infant microbiome to providing biological signals that may influence sleep and circadian rhythms, breast milk does far more that simply feed a baby. It is nourishment, protection, communication and connection delivered in every feed.