Breast Milk

Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by mammary glands located in the breast of a human female. Breast milk is the primary source of nutrition for newborns, containing fat, protein, carbohydrates (lactose and human milk oligosaccharides) and variable minerals and vitamins. Breast milk also contains substances that help protect an infant against infection and inflammation, whilst also contributing to healthy development of the immune system and gut microbiome.

Uses and methods of consumption

The World Health Organization recommends exclusive breastfeeding for the first six months of life, with solids gradually being introduced around this age when signs of readiness are shown. Supplemented breastfeeding is recommended until at least age two and then for as long as the mother and child wish.

Some newborn babies that are alert and healthy have the ability to latch on to the mother's breast within one hour of birth, however, on a global level, 3/5 babies are not breast fed within the first hour of being born. Breast milk can also be pumped from the mother using a breast pump and fed by baby bottle, cup and/or spoon, supplementation drip system, or nasogastric tube. For infants who are born early (preterm birth) and do not have the ability to suck right away, the use of cups to feed expressed milk and other supplements is reported to result in better breastfeeding extent and duration compared with bottles and tube feeding.

For women who do not produce sufficient amounts of breast milk, donor human breast milk that is pasteurized may be effective. If pasteurized donor breast milk is not available, commercial formula is suggested as a second alternative. Breast milk supplied by a woman other than the baby's mother that is not pasteurized and informal breast milk sharing is associated with a risk of transmitting bacteria and viruses from the donor mother to the baby and is not considered a safe 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.

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. A 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. However, it can be argued that human 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 now is almost universally prescribed, in some countries, in the 1950s the practice of breastfeeding went through a period where it was out of vogue and the use of infant formula was considered superior to breast milk. However, it is now universally recognized that there is no commercial formula that can substitute 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 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, however, other health organisations such as the NHS in the UK have no such recommendation. Breast milk contains less iron than formula, because it 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 breastfeeding can occur and the production of the hormone prolactin is necessary to induce breastfeeding (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 complex proteins, lipids, carbohydrates and other biologically active components. 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% to 0.9% protein, 4.5% fat, 7.1% carbohydrates, and 0.2% ash (minerals). Carbohydrates are mainly lactose; several lactose-based 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.

Non-protein nitrogen-containing compounds, making up 25% of the milk's nitrogen, include urea, uric acid, creatine, creatinine, amino acids, and nucleotides. Breast milk has circadian variations; some of the nucleotides are more commonly produced during the night, others during the day.

Mother's milk has been shown to supply endocannabinoids (the natural neurotransmitters that cannabis simulates) 2-Arachidonoyl glycerol, anandamide, oleoylethanolamide, palmitoylethanolamide, N-arachidonoyl glycine, eicosapentaenoyl ethanolamide, docosahexaenoyl ethanolamide, N-palmitoleoyl-ethanolamine, dihomo-γ-linolenoylethanolamine, N-stearoylethanolamine, prostaglandin F2alpha ethanolamides and prostaglandin F2 ethanolamides, Palmitic acid esters of hydroxy-stearic acids (PAHSAs). They may act as an appetite stimulant, but they also regulate appetite so infants don't eat too much. That may be why formula-fed babies have a higher caloric intake than breastfed babies.

Breast milk is not sterile, but contains as many as 600 different species of various bacteria, including beneficial Bifidobacterium breve, B. adolescentis, B. longum, B. bifidum, and B. dentium, which contribute to colonization of the infant gut. As a result, it can be defined as a probiotic food, depending on how one defines " probiotic". Breast milk also contains a variety of somatic cells and stem cells and the proportion of each cell type differs from individual to individual. The somatic cells are mainly lactocytes and myoepithelial cells derived from the mother's mammary glands. The stem cells found in human breast milk have been shown to be able to differentiate into a variety of other cells involved in the production of bodily tissues and a small proportion of these cross over the nursing infant's intestinal tract into the bloodstream to reach certain organs and transform into fully functional cells. Because of its diverse population of cells and multifarious functions, researchers have argued that breast milk should be considered a living tissue.

Breast milk contains a unique type of sugars, human milk oligosaccharides (HMOs), which are not present in infant formula. HMOs are not digested by the infant but help to make up the intestinal flora. They act as decoy receptors that block the attachment of disease causing pathogens, which may help to prevent infectious diseases. They also alter immune cell responses, which may benefit the infant. To date (2015) more than a hundred different HMOs have been identified; both the number and composition vary between women and each HMO may have a distinct functionality.

The breast milk of diabetic mothers has been shown to have a different composition from that of non-diabetic mothers. It may contain elevated levels of glucose and insulin and decreased polyunsaturated fatty acids. A dose-dependent effect of diabetic breast milk on increasing language delays in infants has also been noted, although doctors recommend that diabetic mothers breastfeed despite this potential risk.

Women breastfeeding should consult with their physician regarding substances that can be unwittingly passed to the infant via breast milk, such as alcohol, viruses (HIV or HTLV-1) or medications. Even though most infants infected with HIV contract the disease from breastfeeding, most infants that are breastfed by their HIV positive mothers never contract the disease. While this paradoxical phenomenon suggests that the risk of HIV transmission between an HIV positive mother and her child via breastfeeding is small, studies have also shown that feeding infants with breast milk of HIV-positive mothers can actually have a preventative effect against HIV transmission between the mother and child. This inhibitory effect against the infant contracting HIV is likely due to unspecified factors exclusively present in breast milk of HIV-positive mothers.

Most women that do not breastfeed use infant formula, but breast milk donated by volunteers to human milk banks can be obtained by prescription in some countries. In addition, research has shown that women who rely on infant formula could minimize the gap between the level of immunity protection and cognitive abilities a breastfed child benefits from versus the degree to which a bottle-fed child benefits from them. This can be done by supplementing formula-fed infants with bovine milk fat globule membranes (MFGM) meant to mimic the positive effects of the MFGMs which are present in human breast milk.

Storage of expressed breast milk

Expressed breast milk can be stored. Lipase may cause thawed milk to taste soapy or rancid due to milk fat breakdown. It is still safe to use, and most babies will drink it. Scalding it will prevent rancid taste at the expense of antibodies. It should be stored with airtight seals. Some plastic bags are designed for storage periods of less than 72 hours. Others can be used for up to 12 months if frozen. This table describes safe storage time limits.

Comparison to other milks

All mammalian species produce milk, but the composition of milk for each species varies widely and other kinds of milk are often very different from human breast milk. As a rule, the milk of mammals that nurse frequently (including human babies) is less rich, or more watery, than the milk of mammals whose young nurse less often. Human milk is noticeably thinner and sweeter than cow's milk.

Whole cow's milk contains too little iron, retinol, vitamin E, vitamin C, vitamin D, unsaturated fats or essential fatty acids for human babies. Whole cow's milk also contains too much protein, sodium, potassium, phosphorus and chloride which may put a strain on an infant's immature kidneys. In addition, the proteins, fats and calcium in whole cow's milk are more difficult for an infant to digest and absorb than the ones in breast milk.

The composition of marsupial and monotreme milk contains essential nutrients, growth factors and immunological properties to support the development of joeys and puggles.

* Note: Milk is generally fortified with vitamin D in the U.S. and Canada. Non-fortified milk contains only 2 IU per 3.5 oz.

Effects of medications and other substances on milk content