From the American Academy of Pediatrics:
Extensive research, especially in recent years, documents diverse and compelling advantages to infants, mothers, families, and society from breastfeeding and the use of human milk for infant feeding. These include health, nutritional, immunologic, developmental, psychological, social, economic, and environmental benefits.
Human milk is uniquely superior for infant feeding and is species-specific; all substitute feeding options differ markedly from it. The breastfed infant is the reference or normative model against which all alternative feeding methods must be measured with regard to growth, health, development, and all other short- and long-term outcomes.
Epidemiologic research shows that human milk and breastfeeding of infants provide advantages with regard to general health, growth, and development, while significantly decreasing risk for a large number of acute and chronic diseases. Research in the United States, Canada, Europe, and other developed countries, among predominantly middle-class populations, provides strong evidence that human milk feeding decreases the incidence and/or severity of diarrhea,1-5 lower respiratory infection,6-9 otitis media,3,10-14 bacteremia,15,16 bacterial meningitis,15,17 botulism,18 urinary tract infection,19 and necrotizing enterocolitis.20,21 There are a number of studies that show a possible protective effect of human milk feeding against sudden infant death syndrome,22-24 insulin-dependent diabetes mellitus,25-27 Crohn's disease,28,29 ulcerative colitis,29 lymphoma,30,31 allergic diseases,32-34 and other chronic digestive diseases.35-37 Breastfeeding has also been related to possible enhancement of cognitive development.38,39
There are also a number of studies that indicate possible health benefits for mothers. It has long been acknowledged that breastfeeding increases levels of oxytocin, resulting in less postpartum bleeding and more rapid uterine involution.40 Lactational amenorrhea causes less menstrual blood loss over the months after delivery. Recent research demonstrates that lactating women have an earlier return to prepregnant weight,41 delayed resumption of ovulation with increased child spacing,42-44 improved bone remineralization postpartum45 with reduction in hip fractures in the postmenopausal period,46 and reduced risk of ovarian cancer47 and premenopausal breast cancer.48
In addition to individual health benefits, breastfeeding provides significant social and economic benefits to the nation, including reduced health care costs and reduced employee absenteeism for care attributable to child illness. The significantly lower incidence of illness in the breastfed infant allows the parents more time for attention to siblings and other family duties and reduces parental absence from work and lost income. The direct economic benefits to the family are also significant. It has been estimated that the 1993 cost of purchasing infant formula for the first year after birth was $855. During the first 6 weeks of lactation, maternal caloric intake is no greater for the breastfeeding mother than for the nonlactating mother.49,50 After that period, food and fluid intakes are greater, but the cost of this increased caloric intake is about half the cost of purchasing formula. Thus, a saving of >$400 per child for food purchases can be expected during the first year.51,52
Despite the demonstrated benefits of breastfeeding, there are some situations in which breastfeeding is not in the best interest of the infant. These include the infant with galactosemia,53,54 the infant whose mother uses illegal drugs,55 the infant whose mother has untreated active tuberculosis, and the infant in the United States whose mother has been infected with the human immunodeficiency virus.56,57 In countries with populations at increased risk for other infectious diseases and nutritional deficiencies resulting in infant death, the mortality risks associated with not breastfeeding may outweigh the possible risks of acquiring human immunodeficiency virus infection.58 Although most prescribed and over-the-counter medications are safe for the breastfed infant, there are a few medications that mothers may need to take that may make it necessary to interrupt breastfeeding temporarily. These include radioactive isotopes, antimetabolites, cancer chemotherapy agents, and a small number of other medications. Excellent books and tables of drugs that are safe or contraindicated in breastfeeding are available to the physician for reference, including a publication from the AAP.55