Breast milk - composition & immunomodulatory properties

Mother's milk is the ideal source of nutrition for newborns and provides a precisely balanced mixture of macro and micronutrients, bioactive proteins and immune factors that promote both growth and the development of the immune system. It contains an average of 0.67-0.70 kcal/ml and is made up of carbohydrates, fats, proteins, vitamins and minerals. The main carbohydrate component is lactose, which at around 7 g per 100 ml is a key source of energy and also supports the development of healthy intestinal flora. The fat content varies between 3.5 and 4.5 g per 100 ml and consists of a mixture of saturated and unsaturated fatty acids, including essential long-chain fatty acids, which play an important role in brain development. The proteins contained, approximately 0.9-1.2 g per 100 ml, are composed of caseins and serum proteins, including immunomodulatory molecules such as lactoferrin and immunoglobulins. This composition is supplemented by a variety of vitamins and minerals, including calcium, iron, zinc and the fat-soluble vitamins A, D, E and K.

In addition to its role as a source of nutrition, breast milk has a unique immunoregulatory function that distinguishes it fundamentally from industrial infant formula. Of particular note is lactoferrin, an iron-binding glycoprotein with pronounced antimicrobial, antiviral and anti-inflammatory properties. It contributes to the regulation of iron availability by depriving pathogenic bacteria of the iron necessary for their growth, supports the development of the intestinal barrier and promotes a healthy microbiota. It also acts as a modulator of the immune system by influencing the activity of immune cells. In addition to lactoferrin, immunoglobulin G (IgG) plays an essential role in the passive immunity of the newborn. Transferred to the child via breast milk, IgG offers targeted protection against pathogens and promotes the development of long-term immune memory. In addition, breast milk contains secretory immunoglobulin A (sIgA), which protects the mucous membranes from infections, human milk oligosaccharides (HMOs), which promote the growth of beneficial intestinal bacteria, as well as a variety of cytokines and growth factors that have an anti-inflammatory effect and contribute to immune maturation.

The composition of breast milk is not static, but varies in the different breastfeeding phases to meet the specific needs of the child. While colostrum contains particularly high amounts of immune factors such as lactoferrin and IgG in the first few days after birth, this is followed by transitional milk, which provides an increasing amount of nutrients. Finally, mature breast milk is a balanced mixture of nutrients and protective substances. Whilst industrial infant formula is constantly being developed to come as close as possible to breast milk in its composition, it lacks many of these bioactive components or only contains them in small quantities. Current research is therefore focussing on enriching infant formula with immunomodulatory substances such as lactoferrin or oligosaccharides in order to partially mimic their health benefits. Nevertheless, breast milk remains unique in its ability to optimally support both physiological and immunological development.