Breastfeeding is not a matter of choice, it is a public health matter, strongly stated the section on Breastfeeding of the American Academy of Pediatrics in its policy statement in 2012. The American College of Obstetrics and Gynecology (ACOG) has also signed on to this statement as has the American Academy of Family Practice (AAFP). “The discussion is over, human milk is for human infants” proclaimed Myers at the twenty-fifth Surgeon General’s Workshop in 2009. The evidence is overwhelming. The Old Testament states firmly that women should breastfeed their children. The Koran also indisputably commanded mothers to breastfeed their infants until they were 2 years old. Christians had been conspicuously silent until 1995 when Pope John Paul II spoke out and proclaimed that the women of the world should breastfeed their children.
So why are we still discussing it? The evidence of the value of breastfeeding for both mother and child continues to mount. Along with the dozens of studies confirming what we already knew, there have been published challenging papers where the evidence is carefully culled to present a different picture. Studies analyzing the benefits have compared the “ever breastfed” to the formula-fed child. Ever breastfed includes any infant who went to breast only once. The most challenging problem is setting up a controlled study randomly assigning women to breastfeed or including controls that were not to breastfeed; such a study is neither ethical nor possible. Formula feeding has been called the largest experiment in life with no science to prove it is safe or efficacious. Formula is a necessary commodity only because not all women can or will breastfeed.
The evidence of the benefits of breastfeeding presented here is selected from the best of medical research. There has never been a study done that proves formula is better nor, in fact, even equal. Formula is adequate when human milk is not available.
Compelling Reasons to Breastfeed
Species Specificity
Species specificity encompasses all the benefits of being breastfed for human infants because breast milk is more than just good nutrition. Human breast milk is specific for the needs of human infants, just as the milk of thousands of other mammalian species is specifically designed for their offspring. For optimal growth of brain and body, as well as protection against infection and development of immunity, human milk is specifically designed for all the needs of human infants.
Nutritional Benefits
Many benefits of breastfeeding are related to how children eat rather than what they eat as they get older. Breastfeeding eating is different from bottle-feeding, which depends on the maternal feeding style and her control of the process. The more frequently the infant bottle feeds (regardless of bottle content) the more likely the mother focuses on giving the infant enough. Mother encourages finishing every drop. This continues with later feeding habits to clean the plate and take more. This behavior is often the basic problem with obesity. In breastfeeding, the infant takes what he wants, no more. Feeding at the breast is a satisfying experience so that additional suckling is rarely needed.
The unique composition of breast milk provides the ideal nutrients for human brain growth, especially in the first year of life. Cholesterol, docosahexaenoic acid (DHA), and taurine are particularly important. Cholesterol is part of the fat globule membrane and is present in approximately equal amounts in both cow milk and breast milk. Maternal dietary intake of cholesterol has no impact on breast milk’s cholesterol content. Formula naturally lacks human DHA and taurine. The cholesterol in cow milk, however, has been removed in infant formulas, which are cholesterol-free. These elements—cholesterol, DHA, and taurine—are readily available from breast milk and are essential nutrients for human infants, especially for growth of the brain. Regardless of what additives are manufactured and added to bovine formula, they all have their origin from some other species and have been chemically extracted and subjected to extensive heat.
The maximum bioavailability of essential nutrients, including micro minerals, means that digestion and absorption are highly efficient. Comparison of the biochemical percentages of constituents of breast milk and infant formula fails to reflect the highly efficient bioavailability and utilization of constituents in breast milk compared with modified cow milk, from which only a small fraction of some nutrients is absorbed.
Nourishment with breast milk is a combination event, in which nutrient-to-nutrient interaction is significant. The process of mixing isolated single nutrients in formula does not guarantee the nutrient or nonnutrient benefits that result from breastfeeding. The composition of human milk is a delicate balance of macronutrients and micronutrients, each in the proper proportion to enhance absorption. Ligands bind to some micronutrients to enhance their absorption. Enzymes also contribute to the digestion and absorption of all nutrients. All enzymes and hormones have been destroyed by processing in infant formulas.
An excellent example of balance is the action of lactoferrin, which binds iron to make it unavailable for Escherichia coli , which depends on iron for growth. When the iron is bound, E. coli cannot flourish and the normal flora of the newborn gut, Lactobacillus bifidus (Bifidobacterium bifidum) , can thrive. In addition, the small amount of iron in human milk is almost totally absorbed, whereas only about 10% of the iron in formula is absorbed by the infant. Nutrients such as proteins are examples of constituents in human milk with multiple functions, which include preventing infection and inflammation, promoting growth, transporting micro minerals, catalyzing reactions, and synthesizing nutrients.
Impact on Cardiovascular Health
A study asking the question of whether perinatal supplementation of long-chain polyunsaturated fatty acids prevents hypertension in later life concluded that long-chain polyunsaturated fatty acids depended upon other nutrients as well. Thus it was concluded that breastfeeding the infant can protect against insulin resistance and hypertension in later life. A meta-analysis by Martin et al. involving 15 studies and 17,503 subjects revealed that a small reduction in diastolic blood pressure was associated with breastfeeding, which confers long-term benefits on cardiovascular health. Another study by Martin et al. reported a reduced risk for atherosclerosis by breastfeeding as recorded in the 65-year follow-up of the Boyd Orr Cohort. The Boyd Orr Cohort is an historical cohort based on the Carnegie Survey diet and health in prewar Britain 1937 to 1939. This cohort involves 4999 participants of 1343 families in 16 centers in England and Scotland who participated in a 1-week diet survey when 0 to 19 years old between 1937 and 1939. The trace rate was 88 when they were sent follow-up surveys. In 2002, 2563 of the original cohort were alive and living in Britain. Controlling for numerous variables, socioeconomic status, smoking, and alcohol made little difference. A prospective cohort study of 2512 men between 45 and 59 years of age were studied according to their infant feeding history. There was a positive association between breastfeeding and coronary heart disease mortality and incidence. There was no evidence of a duration-response effect. Breastfeeding was not associated with stature, blood pressure, insulin resistance, total cholesterol (TC), or fibrinogen. These data, however, only compared ever breastfed and bottle fed. Small studies of exclusively breastfed infants have shown breastfeeding impacts blood pressure. Large studies use all subjects if ever breastfed and the significance is muted. Studies of TC and low-density lipoprotein (LDL) cholesterol showed that levels were higher in infants while consuming breast milk which contains cholesterol. (Formula contains no cholesterol.) Levels in adult life are lower in breastfed infants suggesting that breastfeeding has long-term benefits for cardiovascular health. Adult glucose tolerance tests showed lower 120 minute glucose levels in -individuals who had been breastfed.
In this same Boyd Orr Cohort, Martin et al. studied the impact of breastfeeding and social mobility after 60 years. Prevalence of breastfeeding varied from 45% to 86% by district but not with household income, number of siblings, birth order, or social class in childhood. Breastfeeding was associated with upward social mobility; the longer the duration, the greater the probability, an effect that was not explained by other factors. Childhood obesity and infant feeding has also been evaluated by systematic review of published studies on Medline since 1966. , , In 28 studies involving 298,900 subjects providing odds ratios, breastfeeding was associated with a reduced risk for obesity compared to formula-fed infants. Even in six studies adjusted for parental obesity, maternal smoking, and social class the effect was reduced but present.
For decades, growth in infancy had been measured according to data collected on infants who were exclusively formula fed, until the publication of data in the 1990s on the growth curves of infants who were exclusively breastfed. The physiologic growth curves of breastfed infants show a pattern similar to that of formula-fed infants at the 50th percentile, with significantly fewer breastfed infants in the 90th percentile. This is most evident in the examination of the Z-scores, which indicate that formula-fed infants are heavier compared with breastfed infants, meaning that more are obese. , The World Health Organization (WHO) constructed an international study involving seven countries, rich and poor, to record how children should grow. All participants were exclusively breastfed and had good health. The growth curves from these observations are available worldwide and should replace old curves that demonstrate how children grow, the tall and the short, the fat and the thin, the sick and well. These old curves which included all children are mathematical averages of the good and bad. These growth issues are discussed more completely in Chapter 11 .
A study of adolescents, assessing body composition including height, weight, skinfolds, and waist circumferences, showed an effect of being breastfed if “never breastfed” was compared to breastfed over 4 months in a European multicentered study. Breastfeeding for at least 1 year or more had a profound effect on the development of obesity in Hispanic toddlers. Breastfeeding in this group was associated with a reduced intake of sugar-sweetened beverages. ,
Infection Protection
Leukocytes, specific antibodies, and other antimicrobial factors protect breastfed infants against many common infections. Protection against gastrointestinal infections is well documented. Protection against infections of the upper and lower respiratory system and the urinary tract is less recognized but equally well documented. These infections lead to more emergency room visits, hospitalizations, treatments with antibiotics, and health care costs for the infant who is not breastfed.
The incidence of acute lower respiratory infections in infants has been evaluated in a number of studies examining the relationship between respiratory infections and breastfeeding or formula feeding in these infants. These studies confirm that breastfed infants are less likely to be hospitalized for respiratory infection and, if hospitalized, are less seriously ill. In a study of infant deaths from infectious disease in Brazil, the risk for death from diarrhea was 14 times more frequent in formula-fed infants, and the risk for death from respiratory illness was 4 times more frequent.
According to the report from the Agency for Health Research Quality (AHRQ) in 2007, breastfeeding for 4 or more months is associated with a reduction in the risk for hospitalization secondary to lower respiratory tract disease.
The association of wheezing and allergy with infant feeding patterns has also shown a significant advantage to breastfeeding. In a report from a 7-year prospective study in South Wales, the advantage of breastfeeding persisted to age 7 years in nonatopic infants, and in at-risk infants who were breastfed the risk for wheezing was 50% lower (after accounting for employment status, passive smoking, and overcrowding). Breastfeeding is thought to confer long-term protection against respiratory infection as well.
Upper and lower respiratory tract infections have been evaluated in case-control studies, cohort-based studies, and mortality studies in both clinic attended and hospitalized children in many countries of the developed world. , , The results show clearly that breastfeeding has a protective effect, especially in the first 6 months of life. Acute respiratory infections (ARIs) were studied by Vereen et al. because they are a major cause of infant morbidity. Ever breastfed were compared with never breastfed in a cross-sectional analysis of viral severity in 629 mother-infant dyads. When the infant had ARI, breastfeeding was associated with a decreased risk of having lower versus upper respiratory tract infection. A randomized, controlled trial indicated that withholding cow milk and giving soy milk provided no such protective effect. The incidence of acute otitis media in formula-fed infants is dramatically higher than in breastfed infants, , not only because of the protective constituents of human milk but also because of the process of suckling at the breast, which protects the inner ear. When an infant feeds by bottle, the eustachian tube does not close, and formula and secretions are regurgitated in the tubes. Child care exposure increases the risk for otitis media, and bottle-feeding amplifies this risk. , The longer the breastfeeding, the more prolonged the protection.
Immunologic Protection
In addition to the protection provided by breastfeeding against acute infections, epidemiologic studies have revealed a reduced incidence of childhood lymphoma, both acute lymphocytic and acute myelogenous leukemia, , , and type 1 insulin-dependent diabetes, as well as type 2 diabetes and Crohn disease, in infants who have been exclusively breastfed for at least 4 months, compared with formula-fed infants. In a systematic review and meta-analysis of breastfeeding and childhood cancer published in 49 references between 1966 and 2004, the authors report lower risks such as decreased incidence of acute lymphoblastic leukemia, Hodgkin’s disease, and neuroblastoma. These findings were based on “ever breastfed,” not inclusive breastfeeding for 6 months. Within this cohort, a meta-analysis by Kwan et al. strongly supported the impact of breastfeeding on limiting the risk of childhood leukemia. It demonstrated that longer breastfeeding reduced the risk.
Allergy Prophylaxis
Breastfed infants at high risk for developing allergic symptoms such as eczema and asthma by 2 years of age show a reduced incidence and severity of symptoms in early life. Some studies suggest the protective effect continues through childhood. , A significant reduction in risk for childhood asthma at age 6 years was reported by Oddy et al. if exclusive breastfeeding is continued for at least 4 months. Available evidence regarding full-term infants in developed countries suggests that exclusive breastfeeding for at least 3 months is associated with a reduced risk for atopic dermatitis in children with a family history of atopy.
Prolonged breastfeeding may improve subsequent lung function at 10 years old. Forced vital capacity, forced expiratory volume, and peak expiratory flow were measured in 1456 children who were part of the Isle of Wight Study; 196 were not breastfed, 243 were breastfed less than 2 months, 142 were breastfed more than 2 months but less than 4 months, and 374 were breastfed at least 4 months. Lung volume was enhanced in the breastfed children. The authors speculate that the effect on airflow was mediated by lung volume changes, which could be the result of prolonged suckling at the breast, providing a mechanical stimulus to improve the mechanics of ventilation.
Psychological and Cognitive Benefits
The prevailing impression from large epidemiological studies is that being breastfed results in higher cognitive function and higher performance intellectually. Does breastfeeding alter early brain development? Morphometric brain imaging has supported this premise. Increased white matter and subcortical gray matter volume and parietal lobe cortical thickness have been observed. When quiet magnetic resonance imaging (MRI) scans were used to compare measurements of white matter microstructure in 133 healthy children aged 10 months through 4 years who were exclusively breastfed a minimum of 3 months with those formula fed or fed a mixture, the breastfed children had increased white matter in frontal and associated brain regions. Other regions were anatomically consistent with improvements in cognitive and behavior performance measures. The developmental advantages associated with breastfeeding are supported by the hypothesis that breastfeeding promotes healthy neural growth and white matter development, according to investigators.
Nielsen and O’Hara noted that children who had been breastfed were more mature, secure, and assertive, and they progressed farther on the developmental scale than nonbreastfed children. More recently, studies by Lucas et al. and other investigators found that premature infants who received breast milk provided by tube feeding were more advanced developmentally at 18 months and at 7 to 8 years of age than those of comparable gestational age and birth weight children who had received formula by tube. Such observations suggest that breast milk has a significant impact on the growth of the central nervous system. This suggestion is further supported by studies of visual activity in premature infants who were fed breast milk compared with those who were fed infant formula. When similar studies were performed in full-term infants, visual acuity developed more rapidly in the breastfed infants. Even when DHA was added to formula, the performance by breastfed infants was still better.
An 18-year longitudinal study reported by Horwood and Fergusson demonstrates a small but detectable increase in childhood cognitive and educational achievement in infants who were breastfed. The effects were confirmed in a range of measures, including standardized tests, teacher ratings, and academic outcomes in high school and young adulthood. More than 1000 children in New Zealand participated. Children who were breastfed for 8 months or longer had a mean test score at age 18 that was 0.11 to 0.30 standard deviation units higher than those not breastfed.
To examine the association between duration of infant breastfeeding and intelligence in young adult life, Mortensen et al. conducted a prospective longitudinal cohort study of more than 3000 individuals in Denmark born between 1959 and 1961. They concluded that, independent of a wide range of possible confounding factors, a significant positive association between duration of breastfeeding and intelligence test results existed, using two separate intelligence tests.
In an effort to examine the minimum duration of exclusive breastfeeding for optimal neurologic outcome, Bouwstra et al. assessed the quality of general movements at 3 months of 147 breastfeeding, healthy term infants. General movement quality is considered a sensitive marker of neurologic status according to the authors. They demonstrated a positive effect between breastfeeding duration and general movement quality with a saturation effect at about 6 weeks. They concluded that exclusive breastfeeding for at least 6 weeks might improve neurologic outcome.
Evidence-Based Systematic Reviews
In 2007, two careful, comprehensive assessments of the value of human milk and breastfeeding were published: one from the AHRQ, the other from the Department of Child and Adolescent Health and Development of WHO. The AHRQ reviewed the evidence on the effects of short- and long-term breastfeeding on infants and maternal health outcomes in developed countries. More than 9000 abstracts were screened and 400 individual studies reviewed. The data supported a long list of advantages ( Tables 7-1 and 7-2 ) but did not support the increase in cognitive performance. The relationship between breastfeeding and cardiovascular disease was unclear. Maternal risk reduction is noted in Table 7-3 , and only weight loss and osteoporosis reduction was unclear from the studies. The authors did comment that breastfeeding did not mean exclusive breastfeeding. The Irish Nursing Homes Organization (INHO) analysis also reflected a lack of clarity in terms of impact on intellectual performance, cardiovascular disease, and obesity. When the analysis was complete, however, they were able to confirm that long-term subjects who were breastfeeding experienced lower mean blood pressure and TC and higher performance on intelligence tests. The prevalence of overweight and obesity and type 2 diabetes was lower among breastfeeding infants. Although all were statistically significant some differences were modest. The definition of breastfeeding, exclusive or partial, and length of breastfeeding remain significant factors in measuring outcome.
| Full-Term Infant Outcomes | Reduction in Relative Risk |
|---|---|
| Acute otitis media | 50% reduction |
| Atopic dermatitis | Equivocal |
| Gastrointestinal infections | 64% reduction |
| Lower respiratory tract disease | 72% reduction |
| Asthma | 27% reduction |
| Cognitive development | Equivocal because of confounding factors |
| Obesity | 24%, 7%, 4% for each month of breastfeeding |
| Risk for cardiovascular disease | Blood pressure: up to 1.5 monthly reduction; LDL cholesterol: 7.0–7.7 mg/dL reduction; all-cause CV mortality: needs further investigation |
| Type 2 diabetes | 39% reduction (confounders not well controlled) |
| Childhood leukemias | 19% reduction (all); 15% (AML) |
| SIDS | 36% reduction |
| Mother Outcomes | Reduction in Relative Risk |
|---|---|
| Return to prepregnancy weight | Unclear |
| Maternal type 2 diabetes | 2%-12% |
| Osteoporosis | Unclear |
| Postpartum depression | Too few studies |
| Breast cancer | 28% for 12 or more months (4.3% for each year of breastfeeding) |
| Ovarian cancer | 21% |
| Infant | Risk for acute otitis media | No evidence |
| Nonspecific gastroenteritis | Cognitive performance | |
| Severe lower respiratory tract infection | Cardiovascular disease | |
| Atopic dermatitis | Infant mortality is developed | |
| Asthma | ||
| Obesity | ||
| Type 1 and 2 diabetes | ||
| Childhood leukemia | ||
| SIDS | ||
| Necrotizing enterocolitis | ||
| Maternal | Risk for type 2 diabetes | No relationship |
| Breast cancer | Osteoporosis | |
| Ovarian cancer | Return to prepregnancy weight | |
| Postpartum depression | Weight loss? |
Since these two meta-analyses were performed, several new studies have been published that further support advancement in intellectual skills. Breastfeeding for 3 months or longer was found to enhance language skills and motor skills in a cross-sectional study of 22,399 children with concerns about language decreasing the longer they were breastfeeding.
Evidence from a large randomized trial examining breastfeeding and cognitive development in 17,046 healthy breastfeeding infants, 81.5% of whom were followed for 6.5 years, showed exclusive breastfeeding at 3 months of 43.3% in the experimental group and only 6.4% in the control group and a higher rate of breastfeeding at all ages through 12 months. This was part of the Promotion of Breastfeeding Intervention Trial (PROBIT) study group in Belarus. The experimental group had higher mean scores in the Wechsler Abbreviated Scales of Intelligence, which measures both verbal and performance intelligence quotient (IQ). Teachers’ academic ratings were significantly higher.
The authors considered it strong evidence that prolonged and exclusive breastfeeding improves children’s cognitive development.
Using the data from the National Longitudinal Study of Adolescent Health (26,000 schools in the United States) on sibling pairs, it was estimated that the effect of having been breastfed on high school graduation, high school GPA, and college attendance was significant. Cognitive ability and adolescent health seemed interrelated to breastfeeding. A novel approach utilized in 2011 to improve the causal inference in observational studies compared high, middle, and low income cohorts. Breastfeeding was thought by these authors to have a causal relationship to intelligence. The causal effects of breastfeeding on IQ were determined in a systematic review that looked at the role of confounders. Walfisch concluded that the apparent effect on intelligence was due to confounding. Confounding was based on failure to control for parental IQ.
Although data on cognitive ability was impressive, it did not meet AHRQ scrutiny. Nevertheless, evidence continues to mount. The original studies , actually were done on premature infants, measuring visual activity and auditory acuity, both of which are electroencephalographic responses to standard stimuli. The reactions are unrelated to demographics such as intellectual scores or socioeconomic status of the parents. The value of receiving human milk was clearly demonstrated. A more accurate assumption is that breastfeeding allows a child to reach his/her full potential. It is clear that no study has ever suggested that artificial feedings contribute to good brain growth.
Does Breastfeeding Reduce the Risk for Sudden Infant Death Syndrome?
The policy statement for the American Academy of Pediatrics on Sudden Infant Death Syndrome (SIDS) released in 2011 again affirmed the value of supine sleeping for infants and recommends a pacifier for sleep time along with the list of cautions against soft surfaces, soft covers, and toys. It is stated that co-sleeping is a major cause of SIDS. Concern has arisen about co-sleeping deaths occurring in hospitals in the first few days of life. Fifteen deaths and three near deaths were reported occurring between 1999 and 2013 as reported by members of the National Association of Medical Examiners. The problem is believed to be underreported. Associated circumstances were falling asleep while breastfeeding in eight cases, obesity, and swaddling, but all were bed sharing. The committee states that breastfeeding infants are more easily aroused than formula-fed infants, a safety factor. They also state that some epidemiological studies have proven a relationship between breastfeeding and reduction of SIDS, but others have not. The committee acknowledged the value of breastfeeding but did not recommend breastfeeding as a strategy to reduce SIDS.
The recommendation for pacifier use included a delay in beginning a pacifier in a breastfeeding infant until 1 month of age. It is also stated that if the pacifier falls out of the mouth during sleep that it not be reinserted. There is an increased incidence of plagiocephaly from positioning, and the increase in malocclusion and otitis media from pacifier use was acknowledged. A paper published in 2009 by Vennemann et al. reported that the population-based, case-control study of 333 cases of SIDS and 998 matched controls from Germany showed breastfeeding reduced the risk for SIDS by 50% at all ages; 73% of infants died before 6 months of age.
In a letter to the editor in 2014, the Taskforce states that the Taskforce supports the value of breastfeeding in preventing SIDS.
Benefits of Breastfeeding for Mother
Breastfeeding may provide a mother with a number of benefits, which should be included during discussions about making an informed decision regarding how to feed one’s infant.
Empowerment
In addition to clinically proven medical benefits, breastfeeding empowers a woman to do something special for her infant. The relationship of a mother with her suckling infant is considered the strongest of human bonds. Holding an infant to the mother’s breast to provide total nutrition and nurturing creates an even more profound and psychological experience than carrying the fetus in utero. These observations have been tested in animal experiments in which oxytocin and prolactin have triggered parenting behavior with nonpregnant subjects.
In studies of young women enrolled in the Women, Infants, and Children (WIC) program in Kentucky who were randomly assigned to breastfeed or not to breastfeed and who were provided with a counselor/support person throughout the first year postpartum, the women who breastfed changed their behavior. They developed self-esteem and assertiveness, became more outgoing, and interacted more maturely with their infants than did the women assigned to artificial feeding. The women who breastfed turned their lives around by completing school, obtaining employment, and providing for their infants.
Postpartum Recovery
Women who breastfeed return to a prepregnancy state more promptly than women who do not, and they have a lower incidence of obesity in later life ( Box 7-1 ). , The presence of oxytocin stimulates the uterus to contract and involute with each feeding so that the uterus returns to the prepregnant state within 6 weeks. The extra pregnancy tissue storage is utilized in the production of milk, and the return to prepregnancy weight is thus facilitated.
INFANT
- •
Species specificity
- •
Nutritional advantages
- •
Infection protection
- •
Immunologic protection
- •
Allergy prophylaxis
- •
Psychological benefits
- •
MOTHER
- •
Postpartum recovery
- •
Psychological benefits, empowerment
- •
Improved health risks
- •
Decreased Risk for Osteoporosis
The risk for osteoporosis in later life is greatest for women who have never borne an infant, somewhat less for those who have borne infants, and measurably less for those who have borne and breastfed infants. The bone mineral loss experienced during pregnancy and lactation is temporary. Bone mineral density returns to normal after pregnancy and even after extended lactation when mineral density may exceed the original baseline. Serum calcium and phosphorus concentrations are greater in lactating than in nonlactating women. Lactation stimulates the greatest increases in fractional calcium absorption and serum calcitriol after weaning. Postweaning concentrations of parathyroid hormone are significantly higher than in other stages, and urinary calcium loss is significantly lower. Studies reporting the history of fractures in postmenopausal women do not address exclusivity or duration of breastfeeding nor do they account for body mass index (BMI) or hormone replacement therapy.
Maternal Risk for Cardiovascular Disease, Hyperlipidemia, and Diabetes
The occurrence of cardiovascular disease in women has become an urgent consideration since heart attack and stroke have become more common in women. The correlation with breastfeeding and reduction of risk for cardiovascular disease has been reported for more than two decades. The influence of initial infant feeding on cardiorespiratory risk factors in adults in 9377 persons born during 1 week in 1958 in England has been reported by Rudnicka et al. Breastfeeding was described as never breastfeeding, partially or wholly for less than a month, or breastfeeding more than a month. Little impact was found except for reduced waist circumference, waist/hip ratio, and lower odds of obesity. One month of some breastfeeding would hardly be expected to have a long-range impact. On the other hand, a study from the Women’s Health Initiative of over 139,000 women more than 63 years of age with at least one live birth concluded that increased duration of lactation was associated with a lower prevalence of hypertension, diabetes, hyperlipidemia, and cardiovascular disease in women who reported 12 , or more months of lactation in their lifetime. In a study of 1262 women, it was demonstrated that for every 6 months of breastfeeding the risk of developing type II diabetes, was reduced further. It has been suggested that the role of body weight may reduce the effect.
Protection Against Ovarian Cancer
A woman’s increasing number of pregnancies, increasing length of oral contraceptive use, and increasing duration of lactation are generally agreed to be protective against ovarian cancer. When the relationship between lactation and epithelial ovarian cancer was studied from a multinational database, short-term lactation was as effective as long-term lactation in decreasing the incidence of ovarian cancer in developed countries where ovulation suppression may be less prolonged in relation to lactation. In a study of black women, who are known to have a lower incidence of ovarian cancer, breastfeeding for 6 months or longer, as well as four or more pregnancies and oral contraceptive use, further reduced the incidence of ovarian cancer.
Siskind et al. studied the modifying effect of menopausal status on the association between lactation and risk for ovarian cancer in 824 cancer patients and 855 community control subjects. No association was noted in women whose cancer occurred postmenopausally; however, breastfeeding was somewhat protective against ovarian cancer before menopause in this study. Breastfeeding of more than 12 months cumulative duration was associated with a reduction of the risk for ovarian cancer compared with never breastfeeding. Ovarian cancer was reported in the subgroups of pre- and postmenopausal women but had less robust evidence according to the AHRQ report.
Reduced Incidence of Breast Cancer
A mother with a new diagnosis of breast cancer should not nurse her infant in the interest of having definitive treatment immediately because prolactin levels remain high during lactation, and the role of prolactin in the advancement of mammary cancer is still in dispute. Although endogenous prolactin by itself may not be a risk factor, it could, along with sex steroids, contribute to the acceleration of malignant growth. All lumps in the lactating breast are not cancer and are not even benign tumors. The lactating breast is lumpy, and the “lumps” shift day by day. If a mass is located and the physician thinks it should be biopsied, this can be done under local anesthesia without weaning the infant.
Surgeons have performed many such procedures after referrals in the past 40 years without postoperative complications. The diagnosis of a benign mass was made in most cases. Immediate surgery relieved tremendous anxiety without unnecessarily sacrificing breastfeeding. With noninvasive mammary imaging techniques such as ultrasound, computed tomography (CT) scanning, and MRI, careful diagnosis can be made without interfering with lactation and without delaying diagnosis.
Relationship to Breastfeeding
Is cancer more or less common in women who breastfeed? The answer is not easy to find, but in countries where breastfeeding is common, breast cancer is uncommon. In the United States, the incidence of breast cancer has steadily risen while the frequency of breastfeeding has declined. It has been suggested that nursing protects a woman against breast cancer. This concept has been investigated in many international studies. Breastfeeding does not predispose a woman to cancer and may protect her. How breastfeeding-induced mammary differentiation confers protective effects against breast cancer is not understood. Accessing the normal cellular hierarchy of the fully differentiated gland has been compared to the cellular hierarchy of breast cancer subtypes. Shared transcription factors of normal breast stem cells and certain aggressive breast tumors suggest that it is an imbalance of certain gene regulatory networks that causes this disease.
A case-controlled study of 453 white women with breast cancer and 1365 white women without breast cancer from upstate New York showed an inverse relationship between length of breastfeeding and incidence of breast cancer in premenopausal women that has not been seen in postmenopausal women. The authors found this apparent protective effect persisted throughout the childbearing years, with statistical control for age, parity, age at first pregnancy, age of menarche, and education. The women with cancer had had a higher incidence of lactation failure caused by “insufficient milk.” The authors suggest that the significance of this study may be that women who are unsuccessful at lactation are at increased risk for cancer rather than that breastfeeding is protective.
The combination of low parity and late age at first birth was associated with a sevenfold increase in risk for breast cancer at ages 66 to 80 in a study by Lubin et al. of more than 1400 women in Canada. At all ages, the authors found an increased cancer risk associated with relative infertility, benign breast disease, and not breastfeeding.
Marriage has been established as a negative risk factor for breast cancer. Mortality rates for most causes of death are higher among single women than among ever-married women.
The statistics associating pregnancy and breast cancer influence the picture. In an epidemiologic study, the risk for breast cancer had a linear relationship to the time interval between puberty and childbirth. , The risk was reduced by one third for women who bore their first child before 18 years of age compared with those women who had their first infant when they were older. The risk for breast cancer for women who become pregnant before 20 years old was about half that of those who first become pregnant after 25 years of age. Births after the first full-term pregnancy did not influence the statistics. Women whose first pregnancy appeared after 30 to 35 years of age had a risk for breast cancer four times that of nulliparous women in the same age group. ,
The incidence of breast cancer is low among groups who nursed their infants, including lower economic groups, foreign-born groups, and those in sparsely populated areas. , The frequency of breast cancer in mothers and sisters of a woman with breast cancer is two to three times that expected by chance. This influence could be genetic or environmental. Since the isolation of the “breast cancer gene,” women who are at risk are being identified. Cancer actually is equally common on both sides of the family of an affected woman. If breast milk were the cause, it should be transmitted from mother to daughter. When mother-daughter incidence of cancer was studied, no relationship was found to breastfeeding. The association between breastfeeding and the incidence of breast cancer among 89,887 women in the U.S. Nurses Healthy Study was sought through an additional questionnaire. The authors suggest that no important association exists between breastfeeding and the occurrence of breast cancer. Data gathered since 1996 have changed the conclusions about breastfeeding being protective.
Unilateral breastfeeding (limited to the right breast) is a custom of Tanka women of the fishing villages of Hong Kong. Ing et al. investigated the question, “Does the unsuckled breast have an altered risk for cancer?” They studied breast cancer data from 1958 to 1975. Breast cancer occurred equally in the left and the right breasts. Comparison of patients who had nursed unilaterally with nulliparous patients and patients who had borne children but had not breastfed indicated a highly significant increase in risk for cancer in the unsuckled breast. The authors conclude that in postmenopausal women who have breastfed unilaterally, the risk for cancer is significantly higher in the unsuckled breast. They think that breastfeeding may help protect the suckled breast against cancer.
Other authors have suggested that Tanka women are ethnically a separate people and that it is possible that left-sided breast cancer is related to their genetic pool and not to their breastfeeding habits. No mention has been made of other possible influences; for instance, the impact of their role as “fishermen” or any inherent trauma to the left breast.
As early as 1926, Lane-Claypon stated that breasts that never lactated were more liable to become cancerous. Nulliparity and absence of breastfeeding had been considered important risk factors for breast cancer.
In a collective review of the etiologic factors in cancer of the breast in humans, Papaioannou concludes, “Genetic factors, viruses, hormones, psychogenic stress, diet and other possible factors, probably in that order of importance, contribute to some extent to the development of cancer of the breast.”
Gradually, studies have appeared challenging the dogma. Brinton et al., McTiernan and Thomas, and Layde et al. showed the clearly protective effects of breastfeeding. Another example is a study conducted to clarify whether lactation has a protective role against breast cancer in Asian people, regardless of confounding effects of age at first pregnancy, parity, and closely related factors. Similar results were reported by Zheng et al. in a study in Shandong Province, China, in both pre- and postmenopausal women who had a reduced risk for breast cancer. The more months of breastfeeding, the lower the risk. In a hospital-based, case-control study of 521 women with breast cancer and 521 women without breast cancer, statistical adjustment for potential confounders and a likelihood ratio test for linear trend were done by unconditional logistic regression. Total months of lactation, regardless of parity, was the discriminator. Regardless of age at first pregnancy and parity, lactation had an independent protective effect against breast cancer in Japanese women. Breastfeeding over 6 months, regardless of a family history of breast cancer, was protective in a large group of Spanish women whose records were reviewed retrospectively. The authors suggested that the recent increase in breast cancer paralleled the absence of breastfeeding. Although breast cancer incidence is influenced by genetics, stress, hormones, and pregnancy, in most reports, clearly breastfeeding has a protective effect. A systematic review and meta-analysis do not support the theory that BRCA 1 and BRCA 2 mutation carriers are protected from cancer by breastfeeding.
Two large prospective studies , did not report a protective effect of breastfeeding. Populations of 50,274 and 89,887 identified 2130 and 459 patients with breast cancer. The odds ratios indicate 1.01 (0.98 to 1.05) and 0.95 (0.86 to 1.06), respectively. As with most studies of this nature, the cancers are well defined but not the breastfeeding. No attempt was made to note exclusivity and associated amenorrhea. The studies obtained breastfeeding histories when the women were older than 45 years old and included all those who ever breastfed. Insufficient milk supply has not been associated with increased risk of breast cancer when a large number of reports were reviewed by Cohen et al.
The concern for exposure to estrogen early in life has been part of breast cancer assessment. In utero exposure to estrogen is greater in twin pregnancies and when the mother is older. Estrogen levels in smokers, however, are lower. Weiss et al. analyzed cancer risk in a population-based, case-control study in the United States (2202 with breast cancer and 2009 control subjects under 55 years of age). Twins were at greater risk than singletons, but no association with maternal age at delivery was found. A reduced breast cancer risk was seen among women who had themselves been breastfed as infants. Following Cochrane guidelines in performing a Medline search of papers from 1990 to 2002, a reduction of women’s relative risk for breast cancer and a protective effect against ovarian cancer in women who breastfed their children was demonstrated. Results from meta-analyses in the AHRQ report concluded that there was a reduction in the risk for breast cancer in women who breastfeed their infants. A lifetime breastfeeding history of more than 12 months was especially protective.
In an effort to understand the relationship between breastfeeding and breast cancer, Newton points out that over the past two centuries, women have changed from being pregnant or lactating 60% of the time between menarche and menopause to fewer pregnancies and shorter lactation periods. Thus the amount of time a woman lives with unopposed estrogen (the proliferative phase of the menstrual cycle) was 15% in 1800 and 45% in 1996. Case-control epidemiologic studies consistently show a protective effect ( Table 7-4 ). The most important predictors may be duration of the amenorrheal/hypoestrogenic state and the exposure to breast milk as an infant, according to Newton. Breast cancer mortality is disproportionally high in black women of all ages. African-American women who do not breastfeed are at higher risk for aggressive breast cancer according to Palmer. Women with children who never breastfed were more likely to develop estrogen receptor-negative breast tumors compared to those who never had children. Data from 3700 black breast cancer patients revealed the risk of not breastfeeding. A black mother who had four or more children but never breastfed was more likely to develop estrogen receptor-negative breast cancer compared to a woman with only one child whom she breastfed. According to Palmer, breastfeeding represents a modifiable factor that could reduce the number of cases of estrogen-receptor negative breast cancer and reduce the number of African-American women dying from this disease.
