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Breast Milk Composition

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Human breast milk nourishes the infant's growth and development immediately after delivery. Read the article to understand its composition.

Medically reviewed by

Dr. Monica Mathur

Published At August 24, 2023
Reviewed AtAugust 24, 2023


Human breast milk (HBM) is an invaluable source of nourishment for early human life and is vital for the infant's growth and development immediately after delivery. As a result, the World Health Organization and the United Nations Children's Fund advocate exclusive HBM feeding for at least six months after birth and continuing for at least two years. Various baby formulae have been developed in recent years to be more comparable to HBM and are supplemented with breast milk-specific components such as human milk oligosaccharides. Although these formulations share many components with HBM, there is no ideal equivalent for HBM.

What Is Colostrum?

Colostrum is the first milk the breasts make after the baby is born. This thick, sticky breast milk is yellow or orange. Also, it is essential for nourishing and safeguarding the infant as colostrum contains Ig G antibodies and immunity boosters which protect the baby against many viral and bacterial infection in initial months of life. Initially, colostrum produced is about 40 to 50 ml (milliliter) (1.4 to 1.8 fl oz-ounce) over 24 hours. Colostrum is also quite simple to absorb. What it lacks in number, it more than makes up for in quality. Colostrum has the same components as later milk; however, the quantity of these elements is varied since it is suited to the newborn's requirements.

What Are the Properties of Colostrum?

Since it has high quantities of antibodies and white blood cells, colostrum is frequently referred to as a natural immunization. These must be present in the baby's first milk to protect them from infections and illnesses when it leaves the womb. Colostrum's defensive properties are also beneficial to the baby's digestive system. Colostrum covers and closes the porous gut lining of newborns. This is especially critical if the baby is born early since it will be more vulnerable to the deadly gastrointestinal illness called necrotizing enterocolitis.

What Is the Composition of Human Breast Milk?

HBM nutrient content consists of the following -

1. Macronutrients: HBM includes around 87 % to 88 % water, has a specific gravity of 1.030, an osmolarity of approximately 286 mOsm/L (the number of milliosmoles of the solutes per liter of solution), and 124-g/L (grams per liter) solid components as macronutrients, including carbohydrate-7 % (60 to 70 g/L), protein-1 % (8 to10 g/L), and fat-3.8 % (35 to 40 g/L). Mature milk typically comprises 65 to 70 kcal per 100 mL of energy, with fat accounting for around 50 % of the total calorie supply and carbohydrates accounting for 40 %, in contrast to newborn formulae, which have a limited range of composition recommendations based on stringent criteria for infant health impacts.

2. Vitamins: Although HBM is impacted by food in nursing mothers, it usually includes enough vitamins to enable proper child development. However, vitamins D and K may be deficient in exclusively breastfed newborns and require supplementation. Sun exposure and maternal nutrition, which are affected by temperature, season, latitude, skin color, and lifestyle, influence vitamin D levels. HBM often contains less than 1 mg (milligram) of vitamin D or less than 40 IU/L (International units per liter ), which is insufficient to satisfy the needs of babies. HBM produced by solar exposure in breastfeeding moms or conserved throughout pregnancy can provide vitamin D to breastfed infants. However, in babies, the stored vitamin D is rapidly depleted.

3. Minerals: HBM has a lower mineral content than baby formula, but because of its excellent absorption, no further supplementing is necessary during complete nursing. Iron concentration in colostrum is 0.5 to 1.0 mg/L (milligram per liter) and 0.3 to 0.7 mg/L in mature milk, but bioavailability is 20 % to 50 %, which is more effective than in infant formula (4 % to 7 %). As a result, it usually is not essential to feed iron to solely breastfed infants before four to six months of age, and it is then suggested to supply progressively through iron-enriched solid meals.

4. Hormones and Growth Factors: HBM hormones and growth factors also function as bioactive proteins and peptides. Hormone functions in HBM, such as parathyroid hormone, leptin, insulin, apelin, ghrelin, nesfatin-1, adiponectin, obestatin, and their consequences in babies, need to be better understood.

5. Epidermal Growth Factors: These are essential in intestine maturation and repair. Their levels in colostrum are 2,000 times higher than in mature milk and decrease with lactation.

6. Brain-Derived Neurotrophic Factor and Glial Cell-Line-Derived Neurotrophic Factor: They operate on the enteric nervous system and are required for baby gut development.

7. Ciliary Neurotrophic Factor and Other Neuronal Growth Factors: They are detected in HBM for up to 90 days after birth.

8. Insulin-like Growth Factor (IGF) (IGF1 and IGF-2):These are plentiful in colostrum and diminish with breastfeeding; their levels, except IGF-binding protein-2 in the IGF superfamily, are not substantially different between preterm and term milk. The gut absorbs IGF in its bioactive form and transports it to the bloodstream. IGF-1 helps enterocytes survive by shielding them from oxidative stress-induced intestinal damage; it promotes erythropoiesis and helps raise hematocrit.

9. Vascular Endothelial Growth Factors: These are suggested to aid in the regulation of angiogenesis (new blood vessel formation) and the reduction of retinopathy of prematurity damage.

10. Erythropoietin: This hormone promotes the growth of red blood cells and is considered to help avoid preterm anemia. It also helps to tighten intestinal junctions, which may minimize the incidence of necrotizing enterocolitis.

Which Factors Cause Variations in HBM?

HBM composition varies based on the following factors:

  • Maternal nutrition.

  • Mammary gland function.

  • Maternal health.

  • Environmental variables.

The fat level of foremilk produced by the mammary gland is relatively modest and increases with feeding, but hindmilk has a more extensive fat content. Protein and lactose content do not differ considerably among them. Colostrum is low in fat but high in protein (10 %) and contains immune-protective components such as immunoglobulin A (IgA) and lactoferrin.

What Is the Importance of Human Breast Milk?

Various artificial milk kinds have also been tried to replace HBM for newborns. Nonetheless, there is no perfect replacement for HBM at this time. Macronutrients such as carbohydrates, proteins (including immune components), lipids, numerous micronutrients and vitamins, trophic factors, and microbiota and miRNA (micro ribonucleic acid) are components of HBM that are uniquely available in humans and through breastfeeding moms, making them varied and irreplaceable. However, because the diverse components of HBM are best suited for optimal early human growth and development, HBM from a nursing mother who follows a balanced diet remains the most desired nutrition for children.


Certain factors make HBM superior to newborn formulae for humans, and many studies have identified nutritional components in HBM, such as different macronutrients, micronutrients, and immunologic components. Furthermore, many HBM components and their functions have recently been examined using research approaches, such as next-generation sequencing. More excellent knowledge of these HBM components will aid in various areas, including breastfeeding instruction and promoting improved feeding habits, as well as the treatment of high-risk infants, such as those born prematurely, with infections, neurological problems, or gastrointestinal diseases.

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Dr. Monica Mathur
Dr. Monica Mathur

Obstetrics and Gynecology


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