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Breast milk is the milk produced by the breasts (or mammary glands) of a human female for her infant offspring. Milk is the primary source of nutrition for newborns before they are able to eat and digest other foods; older infants and toddlers may continue to be breastfed, either exclusively or in combination with other foods.
The baby nursing from its own mother is the most common way of obtaining breast milk, but the milk can be pumped and then fed by baby bottle, cup and/or spoon, supplementation drip system, or nasogastric tube. Breast milk can be supplied by a woman other than the baby's mother, either via donated pumped milk (generally from a milk bank or via informal milk donation), or when a woman nurses a child other than her own at her breast, a practice known as wetnursing.
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.[1] Breastfeeding offers health benefits to mother and child even after toddlerhood.[2] These benefits include: a twenty-seven percent of normal risk of SIDS for feeding only human milk,[3][4] increased intelligence,[5] decreased likelihood of contracting middle ear infections,[6] cold and flu resistance,[7] a tiny decrease in the risk of childhood leukemia,[8] lower risk of childhood onset diabetes,[9] decreased risk of asthma and eczema,[10] decreased dental problems,[10] decreased risk of obesity later in life,[11] and a decreased risk of developing psychological disorders, including in adopted children.[12][13]
Breastfeeding also provides health benefits for the mother. It assists the uterus in returning to its pre-pregnancy size and reduces post-partum bleeding, as well as assisting the mother in returning to her pre-pregnancy weight. Breastfeeding also reduces the risk of breast cancer later in life.[14][15] Lactation protects both mother and infant from both types of diabetes.[16]
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 equal breast milk. In addition to the appropriate amounts of carbohydrate, protein, and fat, breast milk provides vitamins, minerals, digestive enzymes,[17] and hormones.[17] Breast milk also contains antibodies and lymphocytes from the mother that help the baby resist infections.[18] 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.[19]
At around four to six months of age, the internal iron supplies of the infant, held in the hepatic cells of the liver, are exhausted, hence this is the time that complementary feeding is introduced.[20][21] 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.[22]
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).
Actual inability to produce enough milk is rare, with studies showing that mothers from developing countries experiencing nutritional hardship still produce amounts of milk of similar quality to that of mothers in developed countries.[23] 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: This syndrome 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.[24][25][26][27] It is very helpful to nurse on demand - to nurse when the baby wants to nurse rather than on a schedule. 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 there are risks for even herbal ones,[28] therefore non-pharmaceutical methods should be tried first.[29]
| Fat | |
| total (g/100 ml) | 4.2 |
| fatty acids - length 8C (% ) | trace |
| polyunsaturated fatty acids (%) | 14 |
| Protein (g/100 ml) | |
| total | 1.1 |
| casein 0.4 | 0.3 |
| a-lactalbumin | 0.3 |
| lactoferrin (apo-lactoferrin) | 0.2 |
| IgA | 0.1 |
| IgG | 0.001 |
| lysozyme | 0.05 |
| serum albumin | 0.05 |
| ß-lactoglobulin | - |
| Carbohydrate (g/100 ml) | |
| lactose | 7 |
| oligosaccharides | 0.5 |
| Minerals (g/100 ml) | |
| calcium | 0.03 |
| phosphorus | 0.014 |
| sodium | 0.015 |
| potassium | 0.055 |
| chlorine | 0.043 |
If nutrient supply is found lacking, content is obtained from the mother's bodily stores. The exact composition of breast milk varies from day to day, depending on food consumption and environment, meaning that the ratio of water to fat fluctuates.
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.[31]
The level of Immunoglobulin A (IgA) in breast milk remains high from day 10 until at least 7.5 months post-partum.[32]
Human milk contains 0.8% to 0.9% protein, 4.5% fat, 7.1% carbohydrates, and 0.2% ash (minerals).[33] 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.[34][35]
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.[36]
Non-protein nitrogen-containing compounds, making up 25% of the milk's nitrogen, include urea, uric acid, creatine, creatinine, amino acids, and nucleotides.[37][38] Breast milk has circadian variations; some of the nucleotides are more commonly produced during the night, others during the day.[39]
Mother's milk has been shown to supply a type of endocannabinoid (the natural neurotransmitters that marijuana simulates), 2-Arachidonoyl glycerol.[40]
At one time it was thought that breast milk was sterile, however it is now known that it contains as many as 600 different species of various bacteria, including beneficial Bifidobacterium breve, B. adolescentis, B. longum, B. bifidum, and B. dentium.[41]
It is also now known that breast milk contains a unique type of sugars, oligosaccharides, which are long chains of complex sugars. So far scientists have identified 140 of them and estimate there are about 200. These types of sugars are found nowhere else in nature, and not every mother produces the same ones, since they vary by blood type. However, the oligosaccharides are not digestible by infants and are instead meant to feed the beneficial bacteria that live in the intestine and help to fight infections. Also found in breast milk are endo-cannabinoids, which 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.[42]
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.[43]
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.
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.[44]
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.[45] 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.[46]
| Place of storage | Temperature | Maximum storage time | |
|---|---|---|---|
| In a room | 25 °C | 77 °F | Six to eight hours |
| Insulated thermal bag with ice packs | Up to 24 hours | ||
| In a refrigerator | 4 °C | 39 °F | Up to five days |
| Freezer compartment inside a refrigerator | -15 °C | 5 °F | Two weeks |
| A combined refrigerator and freezer with separate doors | -18 °C | 0 °F | Three to six months |
| Chest or upright manual defrost deep freezer | -20 °C | -4 °F | Six to twelve months |
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.[47][48][49][50] 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.[48][51][52] Evaporated milk may be easier to digest due to the processing of the protein but is still nutritionally inadequate. Some infants are allergic to cow's milk protein, this problem affecting infant formulas derived from cow's milk.[53]
In addition to providing essential nourishment to infants, human milk; i.e., breast milk, has a number of valuable uses, especially medicinal uses, for both children and adults. It has been used medicinally for thousands of years.[54][55] Breast milk contains strong antibodies and antitoxins that many people believe promote healing and better overall health. However, breast milk lacks sterile and antiseptic properties if a nursing mother is infected with certain communicable diseases, such as HIV and CMV, as breast milk can transmit such diseases to infants and other people.[56][57]
Breast milk has been used as a home remedy for minor ailments, such as conjunctivitis, insect bites and stings, contact dermatitis, and infected wounds, burns, and abrasions. Breast milk has also been used alternatively to boost the immune system of ill persons having viral gastroenteritis, influenza, the common cold, pneumonia, etc., because of its immunologic properties. However, breast milk should never be seen or construed as a "cure-all". Some medical experts are convinced that breast milk can induce apoptosis in some types of cancer cells. However, more research and evidence are needed in this area of cancer treatment.[58]
A minority of people, including restaurateurs Hans Lochen of Switzerland and Daniel Angerer of Austria, who operates a restaurant in New York City, have used human breast milk, or at least advocated its use, as a substitute for cow's milk in dairy products and food recipes.[59] Tammy Frissell-Deppe, a family counselor specialized in attachment parenting, published a book, titled A Breastfeeding Mother's Secret Recipes, providing a lengthy compilation of detailed food and beverage recipes containing human breast milk.[60] The animal rights organization known as PETA ignited a firestorm of criticism when it urged a dairy company to replace the cow's milk they use in their ice cream products with human breast milk as a way to stop cattle abuse.[61][62] Human breast milk is not produced or distributed industrially or commercially, because the use of human breast milk as an adult food is considered unusual to the majority of cultures around the world, and most disapprove of such a practice.[63]
Attempts to formulate soap from breast milk have also been made, and those using it claim that its effectiveness as a cleanser is greater than, or equal to, that of traditional soaps.[64]
Environmental pollutants found in breast milk are usually not harmful, and should be considered only when environmental levels are unusually high. In addition, there has been a decrease in environmental levels, also resulting in a decrease breast-milk levels. Pollutants that are of most concern are pesticides, organic mercury, and lead. DDT and dieldrin are unavoidable, and can also be detected in infant formulas.[65] Pesticides and other toxic substances bioaccumulate; i.e., creatures higher up the food chain will store more of them in their body fat. This is an issue in particular for the Inuit, whose traditional diet is predominantly meat. Studies are looking at the effects of polychlorinated biphenyls and persistent organic pollutants in the body; the breast milk of Inuit mothers is extraordinarily high in toxic compounds.[66]
Persistent toxins were first discovered in breast milk in 1951, when a group of mothers were tested for the pesticide DDT. In 1966, a Swedish researcher found that his wife's breast milk contained polychlorinated biphenyls (PCBs) and five years later Sweden banned PCB's, with the United States following a few years later. But because of their widespread use and persistence, they are still the highest-concentration toxins in breast milk. Most scientists maintain that prenatal exposure to PCB's can do real damage. Researchers in the Great Lakes region, the Arctic and the Netherlands found that babies born to mothers with mid- to upper-range background levels of PCB contamination (most likely because of diets rich in contaminated fish and animal products) have reduced immunities against infections, lower I.Q.'s and delayed learning capabilities, with some problems lasting at least into early adolescence. However, researchers were surprised to learn that although the children who were breast-fed had higher PCB levels than children who were not breastfed, they consistently performed better than those who drank formula—breast milk appeared to be at least partly protective against the effects of toxic chemicals.[67]
In 1981 researchers in the U.S. discovered the flame retardant PBDE in stored human milk samples. Testing showed that between the early 70s when the chemical first came into use and up to 1998, levels of PBDE's in breast milk were doubling every five years and levels were found to be 10 to 100 times higher than those of women in Europe and Japan.[67]
In Costa Rica, there have been trials to produce cheese and custard from human milk as an alternative to weaning[68]
A controversial Swiss restaurateur has created a menu based around foods cooked in human breast milk.[69]
An Icecreamist in London's Covent Garden started selling an ice cream named Baby Gaga in February 2011. Each serving costs £14. All the milk was donated by Mrs Hiley who earns £15 for every 10 ounces and calls it a "great recession beater".[70] The ice cream sold out on its first day. Despite the success of the new flavour, the Westminster Council officers removed the product from the menu to make sure that it was, as they said, "fit for human consumption."[71]
There is a market for human breast milk, both in the form of wet nurse service and milk product. As a product, breast milk is exchanged by human milk banks as well as directly between milk donors and customers mediated by websites on the Internet. Human milk banks generally have standardized measures for screening donors and storing the milk, while donors on websites vary in regard to these measures. A study in 2013 came to the result that 74% of breast milk samples from providers found from websites were colonized with Gram-negative bacteria or had more than 10.000 colony-forming units/mL of aerobic bacteria.[72] Growth happens during transit.[72]
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