The Chemistry of Breast Milk

This Research Article has been written by Nutritionist Anum Nazir).She is Senior Lecturer in School of Nutritional sciences At University of Faisalabad).She is active worker for fight against hunger.Her credible work  is mentioned.


Breast milk is a highly complex and variable bio fluid which nourishes the infant and protects the infant from diseases. The composition of breast milk is changed according to the infant age and body requirement.There are three types of breast milk (colostrum, transitional and mature milk). Breast milk contains the anti-microbial and immunomodulatorycomponents and these components impair the gastrointestinal tract infection (Andreas et al., 2015).

Breast milk have bioactive factors these are capable in preventing the Inflammation and increased specific-antibody production, including PAF-acetylhydrolase, antioxidants, interleukins1, 6, 8 and 10, transforming growth factor (TGF), secretory leukocyteprotease inhibitors (SLPI) and defensing. It also contains the components which stimulate  the differentiation and growth of  B cells including high concentrations of intracellular adhesion molecule1 and vascular adhesionmolecule 1 and lower concentrations of solubleS-selectin, L-selectin and CD14 ( Le Doare et al., 2015).

According to a research, human milk is a good source of nutrition and energy for the human infant but nursing usedmilk-based formulas or milk substitutes which are usually recommended in Japan when it is difficult for an infant to bring up  on mother’s milk. Nutrient quantity in formulas for infants are generally modeled on the composition of human milk and one goal of the improvement of infant formulas is to make them even more similar to human milk. (Yamawaki et al., 2005).

The composition of breast milkvaries as follows: with the stage of lactation,within a given day, with the time of day, on the basis of the time since the last feeding and with the age of the mother.The first milk produced by the mother after labor known as colostrum, which is different in appearance, volume and composition. It is low in quantity and high immunological components and it remains for 5 days.

Between 6 and 15 days postpartum, transitional milk appears. This increase in milk production occurs to support the development and nutritional needs of the growing child. During this period, milk is produced in larger amounts, with higher levels of lactose and fat and water soluble vitamins and with smaller amounts of immunologic components. The highest variability in composition among mothers can be observed in transitional milk. Human breast milk is considered almost mature from the 15th day of lactation and fully mature by four to six weeks after labor (Grawoli et al., 2018).

2.Composition of mother milk:


In breast milk lipids are the largest source of energy for infants. The total energy provide from the lipids is 40-55%. Lipids composition is 98% tri-acyl-glycerides and remaining2% consists on diacylglycerides,monoacylglycerides, free fatty acids,phospholipids and cholesterol.

Breast milk have the about 200 fatty acids and these are present in different concentration. Some of them are present in very low amount. Forexample, oleic acid accounts for 30–40 g/100 g fat in breast milk. Like Long-chain polyunsaturated fatty acids, short-chain fatty acids (SCFA) are also present in breast milk and good source of energy. Sphingomyelins is milk fat and good for myelinisation of centralnervous system (Andreas et al., 2015).


There are about 400 different types of protein found in breast milk and these proteins perform specific functions including: providing nutrition, possessing antimicrobial and immunomodulatory activities and stimulate the nutrients absorption. Breast milk contains the three types of protein including caseins, whey and mucin proteins. The classification of whey and casein done according to their solubility and whey proteins are present in solution whilst caseins proteins are present in casein micelles suspended in solution. Whey protein contains the α-lactalbumin, lactoferrin, IgS, serum albumin and lysozyme and human milk have the three types of casein protein : α-, β- andκ-casein.About 80%–90% of breast milk protein produced by lactocytes(Andreas et al., 2015).

2.3.Antibody in mother milk:

Immunoglobulins are present in high concentrations in early period of lactation and these are present in breast milk as secretory IgA(SIgA). These antibodies protect the infant  immunologically and help in the maturation of the immune system. Thedecrease in antibody also reflects the infants’ immune makes the infant gut unable to absorb and digest the whole protein and gutpermeability due to low concentration of antibodies decrease macromolecules absorption (Andreas et al., 2015).

2.4. Carbohydrate:

In breast milk different and complex carbohydrates are present with lactose. Lactose is a disaccharide consisting of glucose covalently bound to galactose. In humans milk lactose is present in high concentration as compared to other is a high energy demands of the human brain. Human milk oligosaccharides (HMO) are also important component of human milk composition and these are the third major component in breast milk. These are present on average 12.9 g/L in mature milk and 20.9 g/L at 4 days post-partum (Andreas et al., 2015).

2.6. Vitamins:

The content of vitamin in human milk is affected by different factors and most important is the maternal intake or nutritional status. When maternal intake of vitamin is low and she cannot provide the adequate amount of vitamins to their infant. When maternal status is adequate then milk vitamin content is also stable.

Fat soluble vitamins are vitamin A, D, E and K.The vitamin A content of human milkis ranged from 200mg/L to 300 to 600mg/L. The concentrartion of vitamin D and its metabolites in human milk range from 0.1 to 1.0 pg/L. These sterols are present in the nonlipid fraction of milk at 1.5% to 6.0%. The content of Vitamin K of human milk is ranged from 1 to 9 pg/L.About 83% of the total vitamin E content of human milk isa-tocopherol and 6-tocopherols are present in small concentrartion.Tocopherols are present in high concentrartion in colostrum (8mg/L), decrease and then stabilize in mature human milk (34mg/L). Tocopherol level can be increased by the high intake ofvitamin E.

Water-Soluble Vitamins: The quantity of vitamin C in mature human milk  is approximately 100 mg/L. The quantity of thiamin is low in early milk (20 pg/L) and increases in mature milk (200 pg/L). Riboflavin content is high in early milk and decreases to 400 to 600 pg/L with the progression of lactation.Folate in breast milk issecreted bound to whey proteins and it is usually present in the excess amount. Other water soluble vitamins are also found in small quantity in the mother milk (Picciano, 2001).

2.7. Minerals:

Major Minerals.The level ofCalcium, phosphorus, and magnesium in human milk changesthroughout the lactation period. Human milk phosphorus quantity decreased from 147mg/L at 3 weeks of lactation to 107mg/L at 26 weeks of lactation. The level of calcium and magnesium is 259 to 248 and 290 to 330 mg/L, respectively. Although serum calcium, magnesium andr phosphorus are important for bone remodeling in infancy.

Trace Minerals. Infirst month of life, breastfed infants are in negative balance for copper, iron, and zinc. Copper andiron contents of milk decrease in early lactation and then stabilize in mature milk at 0.3 mg/L, whereas zinc level continues to decrease. Early milk contains an average of 4 mg/L of zinc; the value at

6 months is 1.1 mg/L and at 1 year are 0.5 mg/L. Maternal diet does not affect the milk concentrations of these minerals(Picciano, 2001).

  1. Benefits of Breast Milk:

The nutritional, emotional, cognitive, and immunologic benefits of human breast milk and breastfeeding are significant. Human milk protects against various pathogens such as viruses, bacteria, and parasites as well as separate clinical illnesses e.g. necrotizing enterocolitis, bacteremia, respiratory tract illness, meningitis, diarrheal disease, and otitis media. The health benefits of breast milk make it one of the most important factors that help in protecting infants against the morbidity and mortality of various infectious diseases (Lawrence and Lawrence, 2004).

There are many other benefits of breast feeding, including reduced rates of allergic reactions and reduced childhood infections where there is a strong family history of atopy but also reduced rates of  infant death syndrome (Horwood et al., 2001).

3.1. Short term effects of breast feeding:

Breast-feeding protects against gastrointestinal infection and ear infections during infancy. In preterm infants, those receive breast milk had a significantly reduced risk of developing systemic infection or necrotising enterocolitis (Fewtrell, 2004).

3.2. Long term effects of breast feeding:

3.2.1. Risk factors for later cardiovascular disease (CVD)

Studies have shown reduced blood pressure during childhood in those who were breast-fed. In infancy breast-feeding is associated with increased total and LDL-cholesterol concentrations but in adult life, it decreased total and LDL-cholesterol level (Fewtrell, 2004).

3.2.2. Obesity:

There are studies that show breast-feeding protects against obesity later in childhood. Those who receive breast milk were found to have lower concentrations of plasma leptin in relation to their fat mass during adolescence than those who fed on a nutrient-enriched preterm formula. These findings suggest that early diet may program physiology of leptin with the potential for later effects on body fatness (Fewtrell, 2004).

3.2.3. Cognitive development:

Many studies suggest a positive correlation between breast-feeding and cognitive development in children and young adults. This effect is due to differences in the composition of formula milk and breast milk (Fewtrell, 2004).

There have been a number of proposed mechanisms to explain the observed association between breast milk exposure and subsequent enhanced cognitive status. Breast milk contain all essential nutrients that may be lacking in formula feeds but are necessary for optimal development (Horwood et al., 2001).

  • Neoplastic disease

Breast-feeding associated with a significantly reduced risk of acute childhood leukaemia, with some evidence for a dose-response effect as increase in duration of breast feeding. Breast-feeding may protect against various other childhood cancers, particularly lymphoma(Fewtrell, 2004).


  1. FEWTRELL, M. 2004. The long-term benefits of having been breast-fed. Current paediatrics, 14, 97-103.
  2. HORWOOD, L., DARLOW, B. & MOGRIDGE, N. 2001. Breast milk feeding and cognitive ability at 7–8 years. Archives of Disease in Childhood-Fetal and         Neonatal Edition, 84, F23-F27.
  3. LAWRENCE, R. M. & LAWRENCE, R. A. 2004. Breast milk and infection. Clinics in perinatology, 31, 501-528.
  4. Le Doare, K., Holder, B., Bassett, A. and Pannaraj, P.S., 2018. Mother’s milk: A purposeful             contribution to the development of the infant microbiota and            Frontiers in immunology9, p.361.

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