Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by the mammary glands in the breasts of humans. Breast milk is the primary source of nutrition for newborn infants, comprising fats, proteins, carbohydrates, and a varying composition of minerals and vitamins. Breast milk also contains substances that help protect an infant against infection and inflammation, such as symbiotic bacteria and other microorganisms and immunoglobulin A, whilst also contributing to the healthy development of the infant's immune system and gut microbiome.
Use and methods of consumption
The World Health Organization (WHO) and UNICEF recommend exclusive breastfeeding with breast milk for the first six months of an infant's life. This period is followed by the incorporation of nutritionally adequate and safe complementary solid foods at six months, a stage when an infant's nutrient and energy requirements start to surpass what breast milk alone can provide. Continuation of breastfeeding is recommended up to two years of age. This guidance is due to the protective benefits of breast milk, which include fewer infections such as diarrhea—a protection not afforded by formula milk.
Breast milk constitutes the sole source of nutrition for exclusively breastfed newborns, supplying all necessary nutrients for infants up to six months. Beyond this age, breast milk continues to be a source of energy for children up to two years old, providing over half of a child's energy needs up to the age of one and a third of the needs between one and two years of age.
Despite the capability of most newborns to latch onto the mother's breast within an hour of birth, globally, sixty percent of infants are not breastfed within this crucial first hour. Breastfeeding within the first hour of life protects the newborn from acquiring infections and reduces risk of death during the neonatal period.
Alternatively, breast milk can be expressed using a breast pump and administered via baby bottle, cup, spoon, supplementation drip system, or nasogastric tube. This method is especially beneficial for preterm babies who may initially lack the ability to suck effectively. Using cups to feed expressed breast milk and other supplements results in improved breastfeeding outcomes in terms of both duration and extent, compared with traditional bottle and tube feeding.
For mothers unable to produce an adequate supply of breast milk, the use of pasteurized donor human breast milk is a viable option. In the absence of pasteurized donor milk, commercial formula milk is recommended as a secondary alternative. However, unpasteurized breast milk from a source other than the infant's mother, particularly when shared informally, carries the risk of vertically transmitting bacteria, viruses (such as HIV), and other microorganisms from the donor to the infant, rendering it an unsafe alternative.
Benefits
Breastfeeding offers health benefits to mother and child even after infancy. These benefits include proper heat production and adipose tissue development, a 73% decreased risk of sudden infant death syndrome, increased intelligence, decreased likelihood of contracting middle ear infections, cold and flu resistance, a tiny decrease in the risk of childhood leukemia, lower risk of childhood onset diabetes, decreased risk of asthma and eczema, decreased dental problems, decreased risk of obesity later in life, and a decreased risk of developing psychological disorders, including in adopted children. In addition, feeding an infant breast milk is associated with lower insulin levels and higher leptin levels compared feeding an infant via powdered-formula. Many of the infection-fighting and immune system related benefits are associated with human milk oligosaccharides.
Breastfeeding also provides health benefits for the mother. It assists the uterus in returning to its pre-pregnancy size and reduces post-partum bleeding, through the production of oxytocin (see Production). Breastfeeding can also reduce the risk of breast cancer later in life. Lactation may also reduce the risk for both mother and infant from both types of diabetes. Lactation may protect the infant from specifically developing Type 2 diabetes, as studies have shown that bioactive ingredients in human breast milk could prevent excess weight gain during childhood via contributing to a feeling of energy and satiety. The lower risk of child-onset diabetes may be more applicable to infants who were born from diabetic mothers. The reason is that while breastfeeding for at least the first six months of life minimizes the risk of type 1 diabetes from occurring in the infant, inadequate breastfeeding in an infant prenatally exposed to diabetes was associated with a higher risk of the child developing diabetes later. There are arguments that breastfeeding may contribute to protective effects against the development of type 1 diabetes because the alternative of bottle-feeding may expose infants to unhygienic feeding conditions.
Though it is almost universally prescribed, in some countries during the 1950s, the practice of breastfeeding went through a period of unpopularity and the use of infant formula was considered superior to breast milk. However, it is since universally recognized that there is no commercial formula that can adequately substitute for breast milk. In addition to the appropriate amounts of carbohydrate, protein, and fat, breast milk provides vitamins, minerals, digestive enzymes, and hormones. Breast milk also contains antibodies and lymphocytes from the mother that may help the baby resist infections. The immune function of breast milk is individualized, as the mother, through her touching and taking care of the baby, comes into contact with pathogens that colonize the baby, and, as a consequence, her body makes the appropriate antibodies and immune cells.
At around four months of age, the internal iron supplies of the infant, held in the hepatic cells of the liver, are exhausted. The American Academy of Pediatrics recommends that at this time that an iron supplement should be introduced. Other health organisations such as the NHS in the UK have no such recommendation. Breast milk contains less iron than formula, but the iron is more bioavailable as lactoferrin, which carries more safety for mothers and children than ferrous sulphate.
Both the AAP and the NHS recommend vitamin D supplementation for breastfed infants. Vitamin D can be synthesised by the infant via exposure to sunlight; however, many infants are deficient due to being kept indoors or living in areas with insufficient sunlight. Formula is supplemented with vitamin D for this reason.
Production
Under the influence of the hormones prolactin and oxytocin, women produce milk after childbirth to feed the baby. The initial milk produced is referred to as colostrum, which is high in the immunoglobulin IgA, which coats the gastrointestinal tract. This helps to protect the newborn until its own immune system is functioning properly. It also creates a mild laxative effect, expelling meconium and helping to prevent the build-up of bilirubin (a contributory factor in jaundice). Male lactation can occur; the production or administration of the hormone prolactin is necessary to induce lactation (see male lactation).
Actual inability to produce enough milk is rare, with studies showing that mothers from malnourished regions still produce amounts of milk of similar quality to that of mothers in developed countries. There are many reasons a mother may not produce enough breast milk. Some of the most common reasons are an improper latch (i.e., the baby does not connect efficiently with the nipple), not nursing or pumping enough to meet supply, certain medications (including estrogen-containing hormonal contraceptives), illness, and dehydration. A rarer reason is Sheehan's syndrome, also known as postpartum hypopituitarism, which is associated with prolactin deficiency and may require hormone replacement.
The amount of milk produced depends on how often the mother is nursing and/or pumping: the more the mother nurses her baby or pumps, the more milk is produced. It is beneficial to nurse when the baby wants to nurse rather than on a schedule. A Cochrane review came to the conclusion that a greater volume of milk is expressed whilst listening to relaxing audio during breastfeeding, along with warming and massaging of the breast prior to and during feeding. A greater volume of milk expressed can also be attributed to instances where the mother starts pumping milk sooner, even if the infant is unable to breastfeed.
Sodium concentration is higher in hand-expressed milk, when compared with the use of manual and electric pumps, and fat content is higher when the breast has been massaged, in conjunction with listening to relaxing audio. This may be important for low birthweight infants. If pumping, it is helpful to have an electric, high-grade pump so that all of the milk ducts are stimulated. Galactagogues increase milk supply, although even herbal variants carry risks. Non-pharmaceutical methods should be tried first, such as pumping out the mother's breast milk supply often, warming or massaging the breast, as well as starting milk pumping earlier after the child is born if they cannot drink milk at the breast.
Composition
Breast milk contains fats, proteins, carbohydrates (including lactose and human milk oligosaccharides), and a varying composition of minerals and vitamins. The composition changes over a single feed as well as over the period of lactation. Changes are particularly pronounced in marsupials.
During the first few days after delivery, the mother produces colostrum. This is a thin yellowish fluid that is the same fluid that sometimes leaks from the breasts during pregnancy. It is rich in protein and antibodies that provide passive immunity to the baby (the baby's immune system is not fully developed at birth). Colostrum also helps the newborn's digestive system to grow and function properly.
Colostrum will gradually change to become mature milk. In the first 3–4 days it will appear thin and watery and will taste very sweet; later, the milk will be thicker and creamier. Human milk quenches the baby's thirst and hunger and provides the proteins, sugar, minerals, and antibodies that the baby needs.
In the 1980s and 1990s, lactation professionals (De Cleats) used to make a differentiation between foremilk and hindmilk. But this differentiation causes confusion as there are not two types of milk. Instead, as a baby breastfeeds, the fat content very gradually increases, with the milk becoming fattier and fattier over time.
The level of Immunoglobulin A (IgA) in breast milk remains high from day 10 until at least 7.5 months post-partum.
Human milk contains 0.8–0.9% protein, 4.5% fat, 7.1% carbohydrates, and 0.2% ash (minerals). Carbohydrates are mainly lactose; several lactose-based oligosaccharides (also called human milk oligosaccharides) have been identified as minor components. The fat fraction contains specific triglycerides of palmitic and oleic acid (O-P-O triglycerides), and also lipids with trans bonds (see: trans fat). The lipids are vaccenic acid, and conjugated linoleic acid (CLA) accounting for up to 6% of the human milk fat.
The principal proteins are alpha-lactalbumin, lactoferrin (apo-lactoferrin), IgA, lysozyme, and serum albumin. In an acidic environment such as the stomach, alpha-lactalbumin unfolds into a different form and binds oleic acid to form a complex called HAMLET that kills tumor cells. This is thought to contribute to the protection of breastfed babies against cancer.