BREAST FEEDING 3 - Role of Exclusive Breastfeeding in Infant Health Outcomes
These oligosaccharides, cytokines, and immunoglobulins regulate gut colonization and development of gut-associated lymphoid tissue and govern differentiation of T cells that play a role in host defense and tolerance.Formula-fed infants also have a smaller thymus than breastfed infants.
These differences in immune system differentiation may underlie the higher incidence of allergic disease observed in formula-fed children. Not breastfeeding may also affect disease risk through exposure to foreign antigens in formula.
Asthma
Multiple studies have examined the association between infant feeding and development of asthma, with mixed results. In a meta-analysis, Ip and colleagues found a 1.7-fold risk (95% CI, 1.2–2.3) of developing asthma among formula-fed children with a positive family history of asthma or atopy and a 1.4-fold risk (95% CI, 1.1–1.7) among those without a family history, compared with those who were breastfed for 3 months or more. Gdalevich and associates compared less than 3 months of exclusive breastfeeding with greater than or equal to 3 months of exclusive breastfeeding and found a 1.9-fold risk (95% CI, 1.3–2.9) among those with a family history of asthma or atopy.
Atopic Dermatitis
Infants with a family history of atopy who were exclusively breastfed for less than 3 months have a 1.7-fold risk of atopic dermatitis (95% CI, 1.1–2.4) compared with infants who are exclusively breastfed.Similar findings were reported in the PROBIT randomized trial of breastfeeding support,where infants who delivered in control hospitals were 1.9 times as likely (95% CI, 1.1–3.2) to develop atopic dermatitis as those who delivered in breastfeeding support intervention hospitals.
Type 1 Diabetes
Epidemiologic studies have reported an association between exposure to cow’s milk antigen and development of type 1 diabetes, although results have been mixed. Less than 3 months of breastfeeding has been associated with a 1.2- (95% CI, 1.1–1.4) to 1.4-fold (95% CI, 1.2–1.5)increased risk of developing type 1 diabetes compared with more than 3 months of breastfeeding. There is some evidence that differential recall between cases and controls may have biased results.
A randomized, controlled trial is currently underway to test whether cow’s milk formula increases development of islet-cell antibodies. Infants at high risk of type 1 diabetes have been randomized to supplementation with hydrolysated formula versus cow’s milk formula. In a pilot study,exposure to cow’s milk-based formula was associated with higher prevalence of islet cell auto-antibodies, providing tentative evidence for a causal association between cow’s milk exposure and type 1 diabetes.
A randomized, controlled trial is currently underway to test whether cow’s milk formula increases development of islet-cell antibodies. Infants at high risk of type 1 diabetes have been randomized to supplementation with hydrolysated formula versus cow’s milk formula. In a pilot study,exposure to cow’s milk-based formula was associated with higher prevalence of islet cell auto-antibodies, providing tentative evidence for a causal association between cow’s milk exposure and type 1 diabetes.
Childhood Cancer
Several studies have examined associations between formula feeding and childhood leukemia based on the hypothesis that immunoreactive factors in breast milk may prevent viral infections implicated in the leukemia pathogenesis.Two meta-analyses found a 1.3-fold higher risk of acute lymphoblastic leukemia (95% CI, 1.1–1.4) among formula-fed children compared with children who were breastfed less than 6 months. Kwan and colleagues also found a 1.2-fold higher risk of acute myeloid leukemia (95% CI, 1.0–1.4) among formula-fed infants compared with infants breastfed more than 6 months.
Infant Feeding and Maternal Health Outcomes
Not breastfeeding or weaning prematurely is associated with health risks for mothers as well as for infants. Epidemiologic data suggest that women who do not breastfeed face higher risk of breast cancer and ovarian cancer, as well as obesity, type 2 diabetes, metabolic syndrome, and cardiovascular disease. As in the pediatric literature, most evidence arises from observational studies, which are subject to confounding by other health behaviors. For maternal health outcomes, associations are generally reported according to lifetime duration across all pregnancies, rather than duration of feeding for each pregnancy.
Lactation and Malignancy
Lactation suppresses ovulation, leading to lactation amenorrhea. In addition, lactogenesis leads to terminal differentiation of breast tissue with potential long-term effects on malignant transformation. These effects may mediate associations between breastfeeding and breast and ovarian cancer.
Breast Cancer
Some studies have suggested that breastfeeding reduces breast cancer risk, but evidence has been mixed. Observational studies relating lactation and breast cancer among postmenopausal women have largely failed to identify an association. Reports from case-control studies suggest a modest inverse association between breastfeeding and premenopausal breast cancer risk, but findings have been inconsistent and limited by potential recall bias.
Longitudinal studies have similarly produced conflicting results. A meta-analysis of 47 studies found that each year of breastfeeding was associated with a 4.3% (95% CI, 2.9–5.8) reduction in risk of invasive breast cancer.In the Nurses’ Health Study II, the association was stronger among women with a first-degree relative with breast cancer.In this group, never breastfeeding was associated with a 2.4-fold increase (95% CI, 1.3–4.5) in incidence of premenopausal breast cancer, compared with ever having breastfed.
Longitudinal studies have similarly produced conflicting results. A meta-analysis of 47 studies found that each year of breastfeeding was associated with a 4.3% (95% CI, 2.9–5.8) reduction in risk of invasive breast cancer.In the Nurses’ Health Study II, the association was stronger among women with a first-degree relative with breast cancer.In this group, never breastfeeding was associated with a 2.4-fold increase (95% CI, 1.3–4.5) in incidence of premenopausal breast cancer, compared with ever having breastfed.
Ovarian Cancer
In case-control studies,never breastfeeding is associated with a 1.3-fold higher (95% CI, 1.1–1.5) risk of ovarian cancer, compared with ever having breastfed. Danforth and colleagues prospectively examined risk of ovarian cancer in the Nurses’ Heath Studies and found that women who had never breastfed faced a 1.5-fold risk (95% CI, 1.0–2.2) of ovarian cancer, compared with women who breastfed for greater than 18 months. These associations may be mediated by antibodies to MUC-1 antigen, which are thought to develop during mastitis.
Lactation and Maternal Metabolism
Breastfeeding poses a substantial metabolic burden on mothers, requiring 500 kcal per day to supply milk for an exclusively breastfed infant. This metabolic load may help mobilize weight gained during pregnancy. In addition, breastfeeding is associated with more favorable glucose levels, lipid metabolism, and blood pressure. Epidemiologic studies suggest that these differences may persist after weaning with significant longterm benefits for mothers.
Dewey and associates compared weight loss during the first year postpartum between 2 groups of women: those breastfeeding less than 3 months and those continuing for more than 1 year. Women who were intentionally dieting to lose weight were excluded from the study. Women in the prolonged breastfeeding group lost 4.4 lbs more than women who weaned at 3 months, and this difference in weight persisted at 2 years postpartum (P < .05). Other studies have found mixed results,suggesting that differences in caloric intake and physical activity may play a greater role in postpartum weight change than breastfeeding.
A randomized, controlled trial in Honduras provides evidence that breastfeeding can mobilize calories for weight loss. Women exclusively breastfeeding were randomized at 4 months postpartum to introduce complementary foods for their infants or continue to breastfeed exclusively.
At 6 months, exclusively breastfeeding mothers had lost 600 g more than those in the complementary feeding group (P < .05), suggesting that more intense lactation mobilizes additional adipose stores.
At 6 months, exclusively breastfeeding mothers had lost 600 g more than those in the complementary feeding group (P < .05), suggesting that more intense lactation mobilizes additional adipose stores.
Differences in metabolism between breastfeeding and formula-feeding women appear to persist into later life. Several authors have found a higher risk of diabetes and the metabolic syndrome among women who have never breastfed compared with those who breastfed for a prolonged period. In the Nurses’ Health Studies, the risk of type 2 diabetes in the 15 years since their last birth was 1.7-fold higher (95% CI, 1.3–2.3) among parous women who never breastfed compared with those who breastfed for a lifetime total of 2 years or more.
Never having breastfed was also linked with a 1.3-fold (95% CI, 1.1–1.6) risk of myocardial infarction compared with lifetime breastfeeding for 2 years or more in the Nurses’ Health Study. Ram and colleagues assessed the prevalence of metabolic syndrome in a cohort of middle-aged women and found a 1.3-fold higher risk (95% CI, 1.0–1.6) among parous women who had never breastfed, compared with those who had ever breastfed. Similarly, in the Women’s Health Initiative, Schwarz and colleagues found a 10% to 20% higher risk of diabetes, hyperlipidemia, and cardiovascular disease among parous women who had never breastfed compared with those who breastfed for 13 to 23 months (P for trend < .001 for all outcomes).
Never having breastfed was also linked with a 1.3-fold (95% CI, 1.1–1.6) risk of myocardial infarction compared with lifetime breastfeeding for 2 years or more in the Nurses’ Health Study. Ram and colleagues assessed the prevalence of metabolic syndrome in a cohort of middle-aged women and found a 1.3-fold higher risk (95% CI, 1.0–1.6) among parous women who had never breastfed, compared with those who had ever breastfed. Similarly, in the Women’s Health Initiative, Schwarz and colleagues found a 10% to 20% higher risk of diabetes, hyperlipidemia, and cardiovascular disease among parous women who had never breastfed compared with those who breastfed for 13 to 23 months (P for trend < .001 for all outcomes).
The Obstetrician’s Role in Promoting and Supporting Breastfeeding
Multiple studies provide evidence that formula feeding is associated with increased risks for infants and mothers compared with breastfeeding. By supporting breastfeeding as the normative way to feed an infant, the obstetrician-gynecologist can play a powerful role in improving health outcomes across 2 generations.
Counseling During Antenatal Care
Most mothers make decisions about infant feeding early in pregnancy. Early in prenatal care, the obstetrician can educate mothers about the health impact of infant feeding and address potential obstacles to breastfeeding. However, many obstetricians underestimate the importance of their advice. In a study of obstetricians and patients at a multispecialty group practice in Massachusetts,just 8% of physicians felt their advice on whether and how long to breastfeed was important, but more than one-third of mothers reported that their provider’s advice on these topics was very important.
Patient perception of clinicians’ opinions is directly correlated with breastfeeding duration. In a study of breastfeeding prevalence at 6 weeks postpartum, DiGirolamo and colleagues found that 70% of women who thought their physician favored breastfeeding were still breastfeeding compared with 54% of those who thought their physician had no preference.
Patient perception of clinicians’ opinions is directly correlated with breastfeeding duration. In a study of breastfeeding prevalence at 6 weeks postpartum, DiGirolamo and colleagues found that 70% of women who thought their physician favored breastfeeding were still breastfeeding compared with 54% of those who thought their physician had no preference.
When counseling patients about breastfeeding, studies suggest asking open-ended questions such as: “What have you heard about breastfeeding?” followed by acknowledging the mother’s concerns and targeting education to her specific needs. For the mother who elects to bottle feed, this approach allows for an open discussion of risks and benefits and ensures informed consent for the feeding decision. Such an approach is more effective than asking a closed-ended question such as: “Are you going to breast- or bottle-feed?”
Physician office participation in formula marketing programs is also a major predictor of breastfeeding outcomes. Howard and colleagues conducted a randomized, controlled trial of promotional materials at the first prenatal visit. Mothers received either a formula company-sponsored information pack on infant feeding or a noncommercial pack of equal value.
Among mothers who were uncertain about their plans to breastfeed, those who received the formula marketing packet were 1.7 (95% CI, 1.2–2.6) times more likely to wean than those who received the noncommercial information. This randomized trial provides compelling evidence that obstetric care providers should not participate in formula marketing programs.
Among mothers who were uncertain about their plans to breastfeed, those who received the formula marketing packet were 1.7 (95% CI, 1.2–2.6) times more likely to wean than those who received the noncommercial information. This randomized trial provides compelling evidence that obstetric care providers should not participate in formula marketing programs.
Physiology of Breastfeeding
Lactation begins with secretory differentiation of breast tissue during pregnancy.Hormonal changes in estrogen, prolactin, progesterone, and IGF-1 cause differentiation of the mammary epithelium in preparation for milk production. Alveoli form by the end of the first trimester of pregnancy. Placental prolactin, placental growth hormone, and human placental lactogen support mammary differentiation and milk formation.
Progesterone produced by the placenta prevents synthesis of mature milk until after birth. Secretory activation occurs as progesterone levels fall and milk production increases from 50 mL/d at birth to approximate 500 mL/d in the first 2 to 3 days after delivery. As production increases, mammary secretions change from colostrum, a clear fluid rich in secretory IgA and lactoferrin, to mature milk, which contains lactose, lipids, and proteins.
Progesterone produced by the placenta prevents synthesis of mature milk until after birth. Secretory activation occurs as progesterone levels fall and milk production increases from 50 mL/d at birth to approximate 500 mL/d in the first 2 to 3 days after delivery. As production increases, mammary secretions change from colostrum, a clear fluid rich in secretory IgA and lactoferrin, to mature milk, which contains lactose, lipids, and proteins.
Milk synthesis occurs continuously, as lactocytes produce lipids, lactose, proteins, and immunoglobulins that comprise human milk. Milk secretion occurs intermittently, when oxytocin stimulates the milk ejection reflex, causing contraction of myoepithelial cells and secretion of milk. Milk let down is inhibited by stressful stimuli.
For the infant to transfer milk, he or she must latch successfully. Infant suckling stimulates release of oxytocin and production of prolactin, and facilitates transfer of milk from the areola to the infant’s mouth. If the breast is not emptied regularly, engorgement occurs. This accumulation of milk in the alveoli appears to downregulate prolactin receptors in the mammary epithelium, leading to reduced milk production.
For the infant to transfer milk, he or she must latch successfully. Infant suckling stimulates release of oxytocin and production of prolactin, and facilitates transfer of milk from the areola to the infant’s mouth. If the breast is not emptied regularly, engorgement occurs. This accumulation of milk in the alveoli appears to downregulate prolactin receptors in the mammary epithelium, leading to reduced milk production.
Successful establishment of lactation requires removal of progesterone and estrogen with delivery of the placenta, followed by a cycle of milk let down, successful latch, and removal of milk. Obstetricians can facilitate this process of “let down, latch, and moving milk” by encouraging immediate skin-to-skin contact after birth, followed by feeding on demand and “rooming in,” keeping the mother and infant together during the postpartum stay. Of note, in a small observational study, Keefe found that mothers who kept infants in their rooms at night slept as much as those who send their infants to the nursery.
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