Lactation is a remarkable process during which the maternal body produces a secretion that provides no immediate benefit to the mother but can totally sustain the offspring. All mammals produce milks with different compositions, each one specific to the needs for growth and development of their offspring. Regardless of a woman's intention to breastfeed, her body prepares for lactation from the first moments of pregnancy: the mammary gland begins its maturational process with the development of the alveolar ductal system and the lacteal cells so that the breast is ready to produce milk upon delivery of the infant. The woman's hormonal balance during pregnancy contributes to the preparation of the breast and promotes accumulation of energy stores, but it suppresses the production of milk until the birth of the infant.
Between 1940 and 1980, there was relatively little active investigation of nutrition during lactation and of the impact of breastfeeding on the mother. Except for the 10 editions of Recommended Dietary Allowances, which have included specific nutrient recommendations for lactating women since they were first published (NRC, 1943), relatively few publications by the National Academy of Sciences, the government, or professional organizations have paid detailed attention to nutrition during lactation. The Academy's publications include three reports prepared by committees of the Food and Nutrition Board under the sponsorship of the Maternal and Child Health Program (Title V, Social Security Act): Nutrition in Pregnancy and Lactation (NRC, 1967), A Selected Annotated Bibliography on Breast-Feeding, 1970-1977 (NRC, 1978), and Nutrition Services in Perinatal Care (NRC, 1981). However, these reports did not include interpretive reviews of the literature.
The first clear evidence that the federal government was increasing its attention to breastfeeding appeared in the report Promoting Health/Preventing Disease: Objectives for the Nation (DHHS, 1980). That publication included an explicit objective to increase the proportion of breastfed infants. The target breastfeeding rates were 75% at hospital discharge and 35% at 6 months post partum. At that time, the Maternal and Child Health Program of the U.S. Department of Health and Human Services (DHHS) was charged with the responsibility of developing national policy related to lactation and breastfeeding and of convening a national group periodically to advise them on specific issues.
Lactation research received increased attention in 1982, when the National Institute of Child Health and Human Development (NICHD) sponsored a conference that dealt primarily with techniques for collection, analysis, and storage of human milk—prerequisites for meaningful studies as well as for milk banking. This was followed by other lactation research conferences (see, for example, FASEB  and Jensen and Neville ).
In 1984, before it was recognized that national rates of breastfeeding had begun to decline (see Chapter 3), Surgeon General C. Everett Koop convened a workshop on Breastfeeding and Human Lactation (DHHS, 1984) and said, ''We must … identify and reduce those barriers which keep women from initiating or continuing to breastfeed their infants" (DHHS, 1984, p. 6). The following six recommendations were made at that workshop to facilitate progress toward the previously mentioned 1990 breastfeeding objective:
Improve professional education in human lactation and breastfeeding
Develop public education and promotional efforts
Strengthen the support for breastfeeding in the health care system
Develop a broad range of support services in the community
Initiate a national breastfeeding promotion effort directed to women in the world of work
Expand research on human lactation and breastfeeding (DHHS, 1985, p. 1).
The publication Followup Report: The Surgeon General's Workshop on Breastfeeding & Human Lactation (DHHS, 1985) summarizes many of the activities that emanated from the recommendations made at the 1984 workshop. Attention to nutrition during lactation fell primarily under the research recommendation.
Between 1985 and 1989, NICHD sponsored three additional lactation-related workshops: the first one on the effects of maternal and environmental factors on human milk (Hamosh and Goldman, 1986), the next one on the effects of milk on the recipient infant (Goldman et al., 1987), and the third one on future needs for human milk research. Statements issued from these workshops and through other forums (e.g., Goldman and Garza, 1987) have clearly indicated that there is a need for additional study of nutrition during lactation and how it may influence the health of both the mother and her infant.
Many of the studies presented at these workshops suggested that breastfeeding might have both immediate and long-lasting beneficial effects.
Despite efforts to promote breastfeeding following the Surgeon General's workshop, breastfeeding rates have declined further, probably because of a combination of social and economic forces. Social attitudes, such as the perceived low value of breastfeeding, may be partially responsible. These attitudes might be expected to continue with the recent adoption of television advertising and direct mail distribution of infant formula by formula manufacturers. Social forces that may be contributing to decreased rates of breastfeeding include the increased participation of women in the work force coupled with the scarcity of job-site day-care facilities and lack of provisions for routine postpartum maternal respite from work. Because of economic pressures on hospitals and cost-containment policies of third-party payers, mothers in many places are routinely discharged 24 hours after delivery, with no opportunity for breastfeeding instruction or support.
These social and economic forces driving the decline of breastfeeding are virtually inseparable from government policies, and current government policies offer little hope of change. The United States is one of the few industrialized countries without a national policy of maternity and parental leave. Moreover, there are few government programs supporting day care. Thus, many mothers must return to work soon after delivery or face the loss of wages or even the loss of a job. Often, they must leave their infants to be cared for at sites distant from their places of employment. The combination of fatigue, stress, and physical separation from their infants makes breastfeeding prohibitive for all but the most strongly committed.
Although nutrition during lactation has not been a priority in breastfeeding promotion efforts, there has been recognition of the need to promote adequate food intake to support milk production and the woman's health. For example, the Special Supplemental Food Program for Women, Infants, and Children (WIC) was encouraged to increase the options for food packages to be more responsive to the food preferences of adolescent mothers and mothers of various ethnic groups.
Many reasons have been given to support breastfeeding promotion (AAP, 1982; AAP/ACOG, 1988; ACOG, 1985; ADA, 1986; APHA, 1983; AAP, 1978; DHHS, 1988):
the favorable balance and bioavailability of nutrients in human milk compared with those of nutrients in formula,
the immunologic properties conferred by human milk that help reduce infant morbidity and mortality during breastfeeding,
the potential for reducing the risk of early development of allergic disease,
the psychologic benefits to both the infant and the mother resulting from the intimate relationship that is repeated throughout the day and night over an extended period,
the facilitation of contractions and the involution of the once gravid uterus and the control of postpartum bleeding associated with oxytocin release,
the maternal feelings of well-being associated with the changes in hormone concentrations during lactation, and
the enhancement of mothering behaviors by the stimulus of hormones during suckling.
The accumulated evidence of the beneficial effects of breastfeeding has led many professional groups (e.g., the American Academy of Pediatrics, the American Dietetic Association, the American College of Obstetricians and Gynecologists, Academy of Family Medicine) to endorse and actively support breastfeeding.
PURPOSE AND SCOPE
In April 1987, the Office of Maternal and Child Health of DHHS asked the Food and Nutrition Board to establish a committee on nutrition during pregnancy and lactation. In response to the request, a committee was formed to oversee the work of three subcommittees: (1) nutritional status and weight gain during pregnancy, (2) dietary intake and nutritional supplementation during pregnancy, and (3) nutrition during lactation. The deliberations of the third subcommittee constitute this report.
The specific charge to the lactation subcommittee was "to evaluate and document the current scientific evidence and formulate recommendations for the nutritional needs of lactating women." Consideration was to be given to the following:
the effect of maternal dietary intake during lactation on the volume and composition of human milk;
the effect of maternal nutritional status during pregnancy and post partum on the volume and composition of human milk;
the appropriateness of various anthropometric methods for assessing nutritional status during lactation; and
the effects of lactation on the recipient infant, maternal health, and maternal nutritional status.
The subcommittee was also asked to consider justification for special recommendations for different maternal age and ethnic groups, taking particular note of the needs of lactating adolescents; women over age 35; and women of black, Hispanic, and Southeast Asian origins. Although there are data on lactation and breastfeeding derived from cultures throughout the world, this report focuses on lactating women and their infants in the United States.
The subcommittee is well aware that nutrient stores and nutrient intake are only two of the many factors that influence production of milk, growth and health of the infant, and maternal health. Other factors (such as hospital practices, the need to resume employment, anatomic adequacy, hormonal response, maternal insecurity, and exposure to infectious agents) are mentioned only briefly in the report, even though they may have great influence on milk volume and composition. The subcommittee restricted its coverage of these factors, however, because they are not directly related to its task. The subcommittee did consider it essential to discuss the components of human milk that may contribute positively or negatively to the health status of infants, even in the absence of data indicating that maternal nutrition might influence those components. Furthermore, the subcommittee also considered it important to place the role of nutrition during lactation in proper perspective relative to the many other factors that can influence the success of breastfeeding.
There remains an urgent need to reduce the many barriers to successful initiation and maintenance of breastfeeding. The reader is encouraged to obtain more information on this from publications such as the Report of the Surgeon General's Workshop on Breastfeeding and Human Lactation (DHHS, 1984) and Promoting Breastfeeding in WIC: A Compendium of Practical Approaches (USDA, 1988).
The Subcommittee on Nutrition During Lactation conducted an extensive review of the literature to examine the impact of lactation on the mother and the infant as well as the impact of maternal diet and nutritional status on maternal stores, the milk, and the infant. Valuable assistance was provided by the Committee on Nutritional Status During Pregnancy and Lactation, which served in an advisory capacity to the subcommittee.
Methods that were used to estimate how lactation influences maternal nutrient requirements included consideration of the nutrient content of human milk and its variability, mean milk production and variations in milk production between and within women, and physiologic changes that may enhance maternal nutrient absorption or reduce nutrient losses.
Imprecise terminology in the literature complicated the subcommittee's task. For example, the terms breastfeeding and breastfed were often used indiscriminately, without definition of extent or duration. Extent of breastfeeding refers to the daily frequency and length of suckling sessions, while duration refers to the number of months or weeks over which breastfeeding occurs. In this report, the subcommittee applies the term exclusive breastfeeding when infants are fed only by this method; partial breastfeeding when breastfeeding is supplemented with limited amounts of formula, juice, water, or solid foods;
and minimal breastfeeding when the infant receives nearly all sustenance from formula and other foods.
Furthermore, terms such as well nourished, malnourished, and undernourished were given various definitions (or none at all) in the literature. The subcommittee uses the term apparently well nourished or, simply, well nourished to describe the healthy woman who is of appropriate weight for height and who has no notable dietary limitations.
The term lactation performance is broadly defined to include the quality and quantity of milk produced, duration of lactation, various indices of maternal health (such as folate status), and selected indices of child health (such as growth and morbidity). When evaluating evidence to determine whether maternal nutrition is likely to influence one or more aspects of lactation performance, careful consideration was given to the adequacy of the study for answering the specific question being addressed. In nearly all cases, the formulation of recommendations required substantial exercise of judgment because of limitations of the data.
ORGANIZATION OF THIS REPORT
This volume begins with a summary of the report and its principal conclusions and recommendations. Chapter 3 addresses the question "Who is breastfeeding?" by identifying breastfeeding rates in the United States by different demographic characteristics (such as age, ethnic background, region of the country, and employment status). It also provides a historical perspective of the incidence and duration of breastfeeding in the past century.
Chapter 4 examines anthropometric and biochemical methods for assessing the nutritional status of lactating women and points out their uses and limitations. The subcommittee tabulated and interpreted nutrient intake data from studies of lactating women.
Chapters 5 and 6 contain discussions of the volume and composition of human milk, respectively, and explain factors that must be considered when evaluating the impact of maternal nutrition on these two lactation outcomes. These chapters also provide the basis for estimating the range of the mother's increased need for nutrients resulting from breastfeeding.
Although infant growth, development, and health are key outcomes of breastfeeding, the effects of maternal nutrition during lactation on these outcomes have been largely ignored in the literature. To the extent possible, Chapter 7 reports the links between the nutrition of the mother and the nutrition and growth of the nursing infant. Since a slower than expected rate of infant weight gain may be given as a reason for discontinuing breastfeeding, the subcommittee paid special attention to the assessment of the growth of breastfed infants. It also raised the possibility that maternal nutrition may influence infant health through altered immunologic function. Links between maternal food intake
while lactating and infant health are also considered in Chapter 7 as they relate to allergic diseases and environmental toxins. To provide a balanced overview of infant health, the risk of transmission of infectious agents via human milk and the presence of drugs in human milk are also covered. In addition, there is brief mention of the development of obesity and atherosclerosis in later life in relation to the method of infant feeding.
Chapter 8 explores ways that maternal health can be influenced by lactation. Topics include obesity, osteoporosis, and breast cancer. Maternal health outcomes also include the impact of lactation on ovulation and fertility. In Chapter 9, information from preceding chapters is synthesized in a discussion of ways to meet the nutrient needs of lactating women. Chapter 10 presents the subcommittee's recommendations for research based on the contents of this report.
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AAP (American Academy of Pediatrics). 1982. The promotion of breastfeeding: policy statement based on task force report. Pediatrics 69:654-661.
AAP/ACOG (American Academy of Pediatrics/American College of Obstetricians and Gynecologists). 1988. Guidelines for Perinatal Care, 2nd ed. American Academy of Pediatrics, Elk Grove, Ill. 356 pp.
ACOG (American College of Obstetricians and Gynecologists). 1985. Standards for Obstetric-Gynecologic Services, 6th ed. The American College of Obstetricians and Gynecologists, Washington, D.C. 109 pp.
ADA (American Dietetic Association). 1986. Position of the American Dietetic Association: promotion of breastfeeding. J. Am. Diet. Assoc. 86:1580-1585.
APHA (American Public Health Association). 1983. Policy statements: breastfeeding. Am. J. Public Health 73:347-348.
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DHHS (Department of Health and Human Services). 1985. Followup Report: The Surgeon General's Workshop on Breastfeeding & Human Lactation. DHHS Publ. No. HRS-D-MC 85-2. Health Resources and Services Administration, Public Health Service, U.S. Department of Health and Human Services, Rockville, Md. 46 pp.
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Jensen, R.G., and M.C. Neville, eds. 1985. Human Lactation: Milk Components and Methodologies. Plenum Press, New York. 307 pp.
NRC (National Research Council). 1943. Recommended Dietary Allowances. Report of the Food and Nutrition Board. Reprint and Circular Series No. 115. National Academy of Sciences, Washington, D.C. 6 pp.
NRC (National Research Council). 1967. Nutrition in Pregnancy and Lactation. Report of the Committee on Maternal Nutrition, Food and Nutrition Board. For Transmittal to the Children's Bureau. National Academy of Sciences, Washington, D.C. 67 pp.
NRC (National Research Council). 1978. A Selected Annotated Bibliography on Breast–Feeding, 1970–1977. Report of the Food and Nutrition Board. National Academy of Sciences, Washington, D.C. 58 pp.
NRC (National Research Council). 1981. Nutrition Services in Perinatal Care. Report of the Committee on Nutrition of the Mother and Preschool Child, Food and Nutrition Board, Assembly of Life Sciences . National Academy Press, Washington, D.C. 72 pp.
USDA (U.S. Department of Agriculture). 1988. Promoting Breastfeeding in WIC: A Compendium of Practical Approaches. FNS–256. Food and Nutrition Service, U.S. Department of Agriculture, Alexandria, Va. 171 pp.