What is breastfeeding?

Process and Effects

The terms breastfeeding, nursing, and
lactation all refer to the best method of infant feeding. The
American Academy of Pediatrics and the World Health Organization recommend
exclusive breastfeeding for the first six months of an infant's life with
continued breastfeeding following the introduction of solid foods up to at least
one year of age and beyond. Although there are a few exceptions, most mothers can
breastfeed and thereby provide low-cost nutritional support for her infant.
Although it is often thought otherwise, the size of the mother’s breast has no
relationship to successful lactation. In fact, the physiology of successful
lactation is determined by the maturation of breast tissue,
the initiation and maintenance of milk secretion, and the ejection or delivery of
milk to the nipple. This physiology is dependent on hormonal control, and nearly
all women have the required anatomy for successful lactation unless they have had
surgical alteration of the breast.

Hormonal influence on breast development begins in adolescence. Increased
estrogen causes the breast ducts to elongate and duct cells
to grow. (The ducts are narrow tubular vessels that run from the segments of the
breast into the tip of the nipple.) More fibrous and fatty tissue develops, and
the nipple area matures. As adolescence progresses, regular menstrual
cycle hormones cause further development of the alveoli,
which are the milk-producing cells.

The elevated levels of estrogen present during pregnancy
promote the growth and branching of milk ducts, while the increase in progesterone
promotes the development of alveoli. Throughout pregnancy and especially during
the first three months, many more milk ducts are formed. Clusters of
milk-producing cells also begin to enlarge, while at the same time placental
hormones promote breast development.

Shortly before labor and delivery, the hormone prolactin is produced by the pituitary
gland. Prolactin, which is necessary for starting lactation
and sustaining milk production, reaches its peak at delivery. Another hormone,
oxytocin, which is also produced by the
pituitary, stimulates the breast to eject milk. This reaction is called the
letdown reflex, which causes the milk-producing alveoli to contract and force milk
to the front of the breast. Oxytocin serves an important function after delivery
by causing the uterus to contract to its prepregnancy size. Initially, the letdown
reflex occurs only when the infant suckles, but later on it may be initiated
simply by the baby’s cry. An efficient letdown reflex is critical to successful
breastfeeding. Emotional upset, fatigue, pain, nervousness, or embarrassment about
lactation can interrupt this reflex; these psychological factors, rather than
breast size or physiology, are predictive of successful lactation.

Breastfeeding is a natural response to childbirth, and the
nutrient content of breast milk is ideal for the human infant. More than one
hundred constituents of breast milk, both nutritive and nonnutritive, are known.
Although the basic nutrient content is a solution of protein, sugar, and salts in
which fat is suspended, those concentrations vary depending on the period of
lactation and even within a given feeding.

Colostrum, often called first milk, is produced in the first few days after birth.
It is lower in fat and calories (kilocalories) and higher in protein and certain
minerals than is mature breast milk. Colostrum is opaque and yellow because it
contains a high concentration of the vitamin A–like substances called carotenes.
It also has a high concentration of antibodies and white blood
cells, which pass on immunologic protection to the
infant.

Within a few days after birth, the transition is made from colostrum to mature
milk. There are two types of mature milk. Foremilk is released first as the infant
begins to suckle. It has a watery, bluish appearance and is low in fat and rich in
other nutrients. This milk accounts for about one-third of the baby’s intake. As
the nursing session progresses, the draught reflex helps move the hindmilk, with
its higher fat content, to the front of the breast. It is important that the
nutrient content of breast milk be determined from a sample of both types of milk
in order to make an adequate assessment of all nutrients present.

Breast milk best meets the infant’s needs and is the standard by which infant
formulas are judged. Several nutrient characteristics make it the ideal infant
food. Lactose, the carbohydrate content of breast milk, is the same simple sugar
found in any milk, but the protein content of breast milk is uniquely tailored to
meet infant needs. An infant’s immature kidneys are better able to maintain water
balance because breast milk is lower in protein than cow’s milk. Most breast milk
protein is alpha-lactalbumin, whereas cow’s milk protein is casein.
Alpha-lactalbumin is easier to digest and provides two sulphur-containing amino
acids that are the building blocks of proteins required for infant growth.

The fat (lipid) content of breast milk differs among women and may even vary day
to day in milk from the same woman. The types of fatty acids
that make up most of the fat component of the milk may vary in response to
maternal diet. Mothers fed a diet containing corn and cottonseed oil produce a
milk with more polyunsaturated fatty acids, which are the predominant fatty acids
in those oils. Breast milk is higher in the essential fatty acid called linoleic
acid than is cow’s milk, and it also contains omega-3 fatty acids. About 55
percent of human milk calories come from fat, compared to about 49 percent of
calories found in infant formulas. In addition, enzymes in breast milk help digest
fat in the infant’s stomach. This digested fat is more efficiently absorbed than
the products that result from digesting cow’s milk or infant formula.

Breast milk contains more cholesterol than cow’s milk, which
seems to stimulate development of the enzymes necessary for degrading cholesterol,
perhaps offering protection against atherosclerosis in later life.
Cholesterol is also needed for proper development of the central nervous
system.

The vitamin and mineral content of breast milk from healthy mothers supplies all
that is needed for growth and health except for vitamin D and fluoride, and these
are easily supplemented. Breast milk and the infant’s intestinal bacteria also
supply all the necessary vitamin K, but since no bacteria are
present at birth, an injection of vitamin K should be given to prevent
deficiencies.

Breast milk mineral content is balanced to promote growth while protecting the
infant’s immature kidneys. Breast milk has a low sodium content, which helps the
immature kidneys to maintain water balance. No type of milk is a good source of
iron. Although breast milk contains relatively small amounts of iron, about 50
percent of this iron can be absorbed by the body, compared to only 4 percent from
cow’s milk. This phenomenon is called bioavailability. Because of the high
bioavailability of breast milk iron, the introduction of solids, which are given
to replace depleted iron stores, can be delayed until six months of age in most
breast-fed infants; this delay may help to reduce the incidence of
allergies in susceptible infants. There is also evidence
that zinc is better absorbed from breast milk.

The vitamin content of milk can vary and is influenced by maternal vitamin status.
The water-soluble vitamin content of breast milk (the B vitamins and vitamin C)
will change more because of maternal diet than the fat-soluble vitamin content
(vitamins A, E, and K). If women have diets that are deficient in vitamins, their
levels in breast milk will be lower. Yet even malnourished mothers can breastfeed,
although the quantity of milk is decreased. As the maternal diet improves, the
level of water-soluble vitamins in the milk increases. There is a level, however,
above which additional diet supplements will not increase the vitamin content of
breast milk.

There are many nonnutritive advantages to breastfeeding. A major advantage is the
immunologic protection and resistance factors that it provides to the infant.
Bifidus factors, found in both colostrum and mature milk, favor the growth of
helpful bacteria in the infant’s digestive tract. These bacteria in turn offer
protection against harmful organisms. Lactoferrin, another resistance factor,
binds iron so that harmful bacteria cannot use it. Lysozyme, lipases, and
lactoperoxidases also offer protection against harmful bacteria.

Immunoglobulins are present in large amounts in colostrum and in significant
amounts in breast milk. These protein compounds act as antibodies against foreign
substances in the body called antigens. Generally, the resistance passed to the
infant is from environmental antigens to which the mother had been exposed. The
concentration of antibodies in colostrum is highest in the first hour after birth.
Secretory IgA is the major immunoglobulin that provides protection against
gastrointestinal organisms. Breast milk also contains interferon, an antiviral
substance that is produced by special white blood cells in milk. Protection
against allergy is another advantage of breastfeeding. It is not known, however,
whether less exposure to the antigens found in formula or some substance in the
breast milk itself provides this protection. Normally, a mucous barrier in the
intestine prevents the absorption of whole proteins, the root of an allergic
reaction. In the newborn, this barrier is not fully developed to allow whole
immunologic proteins to be absorbed. The possibility that whole food proteins will
be absorbed as well is greater if cow’s milk or early solids are given, and this
absorption increases the potential for allergic reactions.

Other possible benefits of breastfeeding are protection against the intestinal
disorders Crohn’s disease and celiac
sprue. The reasons for this protection are not clear. Other
health benefits of breastfeeding in children include a reduced risk for infectious
diseases, including diarrhea and respiratory disease, and a reduced risk of
obesity and type 2 diabetes later in life. Furthermore,
because the taste of breast milk varies with the mother's diet, some studies have
suggested that children who were breastfed as infants are less picky eaters and
more willing to try new foods than children who were exclusively formula-fed.

Breastfeeding also encourages infant bonding, a process in which the mother and
baby form an attachment. It is a matter of controversy whether breastfeeding
mothers bond more easily than bottle-feeding mothers. If a mother has early and
prolonged skin-to-skin contact with her baby, however, the mother is more likely
to breastfeed and to nurse her baby for more months.

Milk from mothers delivering preterm infants is higher in protein and nonprotein
nitrogen, calcium, IgA, sodium, potassium, chloride, phosphorus, and magnesium. It
also has a different fat composition and is lower in lactose than mature milk of
mothers delivering after a normal term. These concentrations support more rapid
growth of a preterm infant.

Breastfeeding is not only good for the baby but also good for the mother. There is
an association between reduced breast cancer rates
and breastfeeding, although the reason is not known. In addition, the hormonal
influences caused by suckling the infant help to contract the uterus, returning it to prepregnancy size and controlling
blood loss. Breastfeeding also helps to reduce the mother’s weight. Calories
required to make milk are drawn from the fat stores that were deposited during
pregnancy. Nevertheless, breastfeeding should be viewed not as a quick weight loss
program but as a healthy, natural weight loss process. Other maternal benefits of
breastfeeding include a reduced risk of ovarian cancer, type 2 diabetes, and
postpartum
depression.

If a woman breastfeeds exclusively, which means that no supplements or solid foods
are given, until the baby is six months of age, often she will not menstruate.
Many women find this lack of menstrual periods psychologically pleasant while not
realizing the physiological benefit of restoring the iron stores that were
depleted during pregnancy and delivery. An important advantage to breastfeeding in
developing countries is that it can help to space pregnancies naturally, as
exclusive pregnancy in the first six months after birth is associated with a low
(1 to 2 percent) likelihood of pregnancy. Most infant malnutrition occurs when the second child is born, because
breastfeeding is stopped for the first child. The first child is weaned to foods
that do not supply enough nutrients. By spacing pregnancies out, the first child
has a chance to nurse longer.

Breastfeeding is very convenient and does not require time to mix and prepare
formula or sterilize bottles. Breast milk is always sterile and at the proper
temperature. The money needed for the extra food required to produce breast milk
is much less than that required to purchase commercial formula. This can be a
major benefit for women with low incomes and is critically important for the
health of those babies born in developing countries.

Complications and Disorders

Some special problems or circumstances can make breastfeeding difficult. The
breasts may become engorged—so full of milk that they are hard and sore—making it
difficult for the baby to latch onto the nipple. Gentle massaging of the breasts,
especially with warm water or a heating pad, will allow release of the milk and
reduce pain in the breast. Using a breast pump to encourage milk expression is
also helpful to reduce breast engorgement. This situation is common during the
first few weeks of nursing but will occasionally recur if a feeding is missed or a
schedule changes.

Sometimes a duct will become plugged and form a hard lump. Massaging the lump and
continuing to nurse will remedy the situation. If influenza-like symptoms
accompany a plugged duct, the cause may be a breast infection known as
mastitis. Since the infection is in the tissue around the
milk-producing glands, the milk itself is safe. The mother must apply heat, get
plenty of rest, maintain hydration, and keep emptying the breast at least every
six hours. Stopping nursing would plug the duct further, making the infection
worse. A short course of antibiotics may be needed to control the infection.

Of concern to many mothers are reports of contaminants in breast milk. Drugs,
environmental pollutants, viruses, caffeine, alcohol, and food allergens can be
passed to the infant through breast milk. Drug transmission depends on the drug's
administration method, which influences the speed with which it reaches the blood
supply to the breast. Whether that drug can remain functional after it is
subjected to the acid in the baby’s digestive tract varies. Large amounts of
caffeine in breast milk can produce a wakeful, hyperactive infant, but this
situation is corrected when the mother curtails her caffeine consumption. Large
amounts of alcohol in breast milk can cause sleep disturbances in infants.
Nicotine also enters milk, but the impact of secondhand
smoke may pose more of a health threat than the nicotine
content of breast milk. Mothers who smoke are encouraged to quit; however,
although nicotine may be present in breast milk, adverse effects to the breastfed
infant have not been reported. The American Academy of Pediatrics encourages
breastfeeding mothers to consider smoking cessation,
but it does not indicate that mothers who smoke cannot breastfeed, as the benefits
of breastfeeding greatly outweigh the risks. Since the human immunodeficiency
virus (HIV), the virus that causes acquired immunodeficiency syndrome (AIDS), can
also pass through breast milk, HIV-positive mothers should not breastfeed their
infants.

Of greater concern is the presence of contaminants that cannot be avoided, such as
pesticide residues, industrial waste, or other environmental contaminants.
Polychlorinated biphenyls (PCBs) and the
pesticide DDT have received the most attention;
however, both DDT and PCBs were banned in the United States in 1972 and 1979,
respectively. Many countries worldwide have also banned the agricultural and
commercial use of these substances. Nevertheless, PCBs may be present in products
that were produced before the ban. Long-term exposure to contaminants promotes
their accumulation in the mother’s body fat, and the production of breast milk is
one way to rid the body of these contaminants. Concentrations present in the
breast milk vary. Ordinarily, these substances are in such small quantities that
they pose no health risk. Women who have consumed large amounts of fish from
PCB-contaminated waters or have had occupational exposure to this chemical,
however, may need to have their breast milk tested. It is also possible for these
substances to enter the infant’s food supply from other sources.

Perspective and Prospects

Although breastfeeding is the best method of infant feeding, many women choose not
to breastfeed. Before the eighteenth century, human milk was the only source for
infant feeding. If a mother did not breastfeed, another woman called a wet nurse
fed her baby. At the end of the nineteenth century, formula feeding became popular
when bottles were developed and water sanitation improved. In the United States,
the percent of infants who begin breastfeeding declined to only about 20 percent
by 1970 but increased to more than 77 percent by 2013, according to the US Centers
for Disease Control and Prevention (CDC). Of infants born in the United States in
2010, 49 percent were breastfed until they were at least six months of age, up
from 35 percent in 2000, according to the CDC's United States 2013 Breastfeeding
Report Card. The breastfeeding rate at the age of twelve months increased from 16
to 27 percent between 2000 and 2010.

Breastfeeding used to be more prevalent among more-educated, higher-income
mothers. Increased employment of women outside the home, however, dramatically
altered trends in breastfeeding. Although mothers may opt to breastfeed in the
hospital, many quit because they are returning to work and believe that it would
be too difficult to continue. A working mother needs four to six weeks at home to
establish successful breastfeeding. Mothers who are unable to maintain a regular
breastfeeding schedule because of work or other obligations often use pumps to
collect milk that can then be stored, thus allowing infants to benefit from
nutritious breast milk even when their mothers are absent and enabling women to
return to their normal schedules.

Formula use increased in developing countries throughout the mid-twentieth
century. Because formula is very expensive, it is often diluted with water and
therefore does not provide enough nutritional support to the infant. The quality
of water is often poor, which causes the infant to be exposed to disease-causing
organisms. In addition, formula-fed infants do not receive the immunologic
protection of breast milk. The result is a higher infant mortality rate.

There are a few instances in which a woman cannot or should not breastfeed her
infant. Women who have had certain surgeries to their breasts, including
mastectomy, breast augmentation, and breast reduction surgeries, may not be able
to express breast milk. Babies with a rare genetic disorder called
galactosemia cannot nurse, since they
lack the enzyme to metabolize milk sugar. Phenylketonuria (PKU), another genetic disorder, requires
close monitoring of the infant’s blood phenylalanine level, but the infant often
can be totally or at least partially breastfed. Breastfeeding is contraindicated
for women suffering from HIV/AIDS, alcoholism, drug addiction, malaria, active
tuberculosis, or a chronic disease that results in maternal malnutrition. The
presence of other conditions, from diabetes to the common cold, is not a reason to
avoid breastfeeding.

One difficulty that some breastfeeding mothers face is backlash to breastfeeding
in public spaces. Although the vast majority of US states and several European
countries have enacted laws that allow women to breastfeed in any public location,
many other countries have no laws that address breastfeeding in public. Many
breastfeeding mothers report being asked to leave restaurants and stores or to
cover up when nursing their infants in public. Critics argue that breastfeeding in
public is inappropriate, while breastfeeding advocates argue that discouraging
women from nursing their hungry babies while in public amounts to child abuse.
Others have argued that many people's discomfort with public breastfeeding stems
from a widespread cultural fetishization of women's breasts that ignores the most
basic biological purpose of breasts—lactation and nursing.

Throughout the 1990s and 2000s, forty-six states in the United States enacted laws
that allow women to breastfeed in any public or private location, while
twenty-nine states also have laws that exempt breastfeeding women from public
indecency laws. Five states, including California, Illinois, Minnesota, Missouri,
and Vermont, as well as Puerto Rico, have implemented breastfeeding awareness
campaigns to increase the public's understanding of the health benefits of
breastfeeding. The 2010 Patient Protection and Affordable Care Act (ACA), a US
federal law, included a provision that amended the 1938 Fair Labor Standards Act
to require that employers give nursing employees a reasonable amount of break time
to express milk for up to one year after the birth of their child; this break time
is not required to be paid. The ACA also requires employers to provide a place
other than a bathroom for nursing employees to express milk; this requirement is
waived for employers with fewer than fifty employees if it causes undue hardship.
In recognition of the many health benefits of breastfeeding, the ACA also requires
new private health insurance plans to provide coverage of women's preventative
health services, including breastfeeding support, breast pumps, and lactation
consultations.

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