Research Notes: Breastfeeding

Pediatrics. 2002 Aug.
Breastfeeding and infant growth: biology or bias?
Kramer MS, Guo T, Platt RW, Shapiro S, Collet JP, Chalmers B, Hodnett E, Sevkovskaya Z, Dzikovich I, Vanilovich I; PROBIT Study Group.
Department of Pediatrics, McGill University Faculty of Medicine, Montreal, Quebec, Canada.

Background: Available evidence suggests that prolonged and exclusive breastfeeding is associated with lower infant weight and length by 6 to 12 months of age. This evidence, however, is based on observational studies, which are unable to separate the effects of feeding mode per se from selection bias, reverse causality, and the confounding effects of maternal attitudinal factors. Design/Methods: A cluster-randomized trial in the Republic of Belarus of a breastfeeding promotion intervention modeled on the World Health Organization (WHO)/UNICEF Baby-Friendly Hospital Initiative versus control (then current) infant feeding practices. Healthy, full-term, singleton breastfed infants (n = 17 046) weighing > or =2500 g were enrolled soon after birth and followed up at 1, 2, 3, 6, 9, and 12 months old for measurements of weight, length, and head circumference. Data were analyzed according to intention-to-treat, while accounting for within-cluster correlation. To assess the potential for bias in observational studies of breastfeeding, we also analyzed our data as if we had conducted an observational study by ignoring treatment, combining the 2 randomized groups, and comparing 1378 infants weaned in the first month and those breastfed for the full 12 months of follow-up with either > or =3 months (n = 1271) or > or =6 months (n = 251) of exclusive breastfeeding. Results: Infants from the experimental sites were significantly more likely to be breastfed (to any degree) at 3, 6, 9, and 12 months and were far more likely to be exclusively breastfed at 3 months (43.3% vs 6.4%). Mean birth weight was nearly identical in the 2 groups (3448 g, experimental; 3446 g, control). Mean weight was significantly higher in the experimental group by 1 month of age (4341 vs 4280 g). The difference increased through 3 months (6153 g vs 6047 g), declined slowly thereafter, and disappeared by 12 months (10564 g vs 10571 g). Analysis by z scores confirmed that infants in both groups gained more weight than the WHO/Centers for Disease Control and Prevention reference, with no evidence of undernutrition in the control group. Length followed a similar pattern. In the observational analyses, infants weaned in the first month were slightly lighter and shorter at birth and their weight-for-age and length-for-age z scores declined by 1 month, but they caught up to both experimental and the other observational groups by 6 months and were heavier and longer by 12 months. Among infants in the 2 prolonged and exclusive breastfeeding groups, weight-for-age z scores fell slightly between 3 and 12 months; length-for-age fell below the reference by 6 months with catch-up to the reference by 12 months. Head circumference showed no significant differences at any age between the 2 trial groups or among the observational groups. Conclusions: Our data, the first in humans based on a randomized experiment, suggest that prolonged and exclusive breastfeeding may actually accelerate weight and length gain in the first few months, with no detectable deficit by 12 months old. These results add support to current WHO and UNICEF feeding recommendations. Our observational analysis showing faster weight and length gains with early weaning and slower gains with prolonged and exclusive breastfeeding may reflect unmeasured confounding differences or a true biological effect of formula feeding.

JAMA. 2002 May 8.
The Association Between Duration of Breastfeeding and Adult Intelligence.
Erik Lykke Mortensen, PhD; Kim Fleischer Michaelsen, MD,ScD; Stephanie A. Sanders, PhD; June Machover Reinisch, PhD.
Danish Epidemiology Science Center, Institute of Preventive Medicine, Copenhagen University Hospital, Denmark (Drs Mortensen and Reinisch); Department of Health Psychology, Institute of Public Health, University of Copenhagen, Denmark (Dr Mortensen); Research Department of Human Nutrition, The Royal Veterinary and Agricultural University, Frederiksberg, Denmark (Dr Michaelsen); The Kinsey Institute for Research in Sex, Gender and Reproduction (Drs Sanders and Reinisch) and Gender Studies (Dr Sanders), Indiana University, Bloomington. [ JAMA ]

Context. A number of studies suggest a positive association between breastfeeding and cognitive development in early and middle childhood. However, the only previous study that investigated the relationship between breastfeeding and intelligence in adults had several methodological shortcomings. Objective. To determine the association between duration of infant breastfeeding and intelligence in young adulthood. Design, Setting, and Participants. Prospective longitudinal birth cohort study conducted in a sample of 973 men and women and a sample of 2280 men, all of whom were born in Copenhagen, Denmark, between October 1959 and December 1961. The samples were divided into 5 categories based on duration of breastfeeding, as assessed by physician interview with mothers at a 1-year examination. Main Outcome Measures. Intelligence, assessed using the Wechsler Adult Intelligence Scale (WAIS) at a mean age of 27.2 years in the mixed-sex sample and the Børge Priens Prøve (BPP) test at a mean age of 18.7 years in the all-male sample. Thirteen potential confounders were included as covariates: parental social status and education; single mother status; mother's height, age, and weight gain during pregnancy and cigarette consumption during the third trimester; number of pregnancies; estimated gestational age; birth weight; birth length; and indexes of pregnancy and delivery complications. Results. Duration of breastfeeding was associated with significantly higher scores on the Verbal, Performance, and Full Scale WAIS IQs. With regression adjustment for potential confounding factors, the mean Full Scale WAIS IQs were 99.4, 101.7, 102.3, 106.0, and 104.0 for breastfeeding durations of less than 1 month, 2 to 3 months, 4 to 6 months, 7 to 9 months, and more than 9 months, respectively (P = .003 for overall F test). The corresponding mean scores on the BPP were 38.0, 39.2, 39.9, 40.1, and 40.1 (P = .01 for overall F test). Conclusion. Independent of a wide range of possible confounding factors, a significant positive association between duration of breastfeeding and intelligence was observed in 2 independent samples of young adults, assessed with 2 different intelligence tests.

Cochrane Database Syst Rev. 2002.
Optimal duration of exclusive breastfeeding.
Kramer MS, Kakuma R.
McGill University, Faculty of Medicine, 1020 Pine Avenue West, Montreal, Quebec, Canada.

Backgound: Although the health benefits of breastfeeding are widely acknowledged, opinions and recommendations are strongly divided on the optimal duration of exclusive breastfeeding. Much of the debate has centered on the so-called 'weanling's dilemma' in developing countries: the choice between the known protective effect of exclusive breastfeeding against infectious morbidity and the (theoretical) insufficiency of breast milk alone to satisfy the infant's energy and micronutrient requirements beyond four months of age. The debate over whether to recommend exclusive breastfeeding for four to six months versus 'about six months' has recently become heated and acrimonious. Objectives: The primary objective of this review was to assess the effects on child health, growth, and development, and on maternal health, of exclusive breastfeeding for six months versus exclusive breastfeeding for three to four months with mixed breastfeeding (introduction of complementary liquid or solid foods with continued breastfeeding) thereafter through six months. A secondary objective was to assess the child and maternal health effects of prolonged (greater than six months) exclusive breastfeeding versus exclusive breastfeeding for six months followed by mixed breastfeeding thereafter. Search strategy: Two independent literature searches were carried out, together comprising the following databases: MEDLINE (as of 1966), Index Medicus (prior to 1966), CINAHL, HealthSTAR, BIOSIS, CAB Abstracts, EMBASE-Medicine, EMBASE-Psychology, Econlit, Index Medicus for the WHO Eastern Mediterranean Region, African Index Medicus, Lilacs (Latin American and Caribbean literature), EBM Reviews-Best Evidence, the Cochrane Database of Systematic Reviews (The Cochrane Library Issue 3, 2000), and the Cochrane Controlled Trials Register (The Cochrane Library Issue 3, 2000). No language restrictions were imposed. The two searches yielded a total of 2,668 unique citations. Contacts with experts in the field yielded additional published and unpublished studies. Selection criteria: We selected all internally-controlled clinical trials and observational studies comparing child or maternal health outcomes with exclusive breastfeeding for six or more months versus exclusive breastfeeding for at least three to four months with continued mixed breastfeeding until at least six months. Studies were stratified according to study design (controlled trials versus observational studies), provenance (developing versus developed countries), and timing of compared feeding groups (three to seven months versus later). Data collection and analysis: Two reviewers independently assessed study quality (using a priori assessment criteria) and extracted data. Main results: Twenty independent studies meeting the selection criteria were identified by the literature search: nine from developing countries (two of which were controlled trials in Honduras) and 11 from developed countries (all observational studies). The two trials did not receive high methodologic quality ratings but were nonetheless superior to any of the observational studies included in this review. The observational studies were of variable quality; in addition, their nonexperimental designs were not able to exclude potential sources of confounding and selection bias. Definitions of exclusive breastfeeding varied considerably across studies. Neither the trials nor the observational studies suggest that infants who continue to be exclusively breastfed for six months show deficits in weight or length gain, although larger sample sizes would be required to rule out modest differences in risk of undernutrition. The data are conflicting with respect to iron status, but at least in developing country settings where newborn iron stores may be suboptimal, suggest that exclusive breastfeeding without iron supplementation through six months may compromise hematologic status. Based primarily on an observational analysis of a large randomized trial in Belarus, infants who continue exclusive breastfeeding for six months or more appear to have a significantly reduced risk of one or more episodes of gastrointestinal infection. No significant reduction in risk of atopic eczema, asthma, or other atopic outcomes has been demonstrated in studies from Finland, Australia, and Belarus. Data from the two Honduran trials suggest that exclusive breastfeeding through six months is associated with delayed resumption of menses and more rapid postpartum weight loss in the mother. Reviewer's conclusions: We found no objective evidence of a 'weanling's dilemma'. Infants who are exclusively breastfed for six months experience less morbidity from gastrointestinal infection than those who are mixed breastfed as of three or four months, and no deficits have been demonstrated in growth among infants from either developing or developed countries who are exclusively breastfed for six months or longer. Moreover, the mothers of such infants have more prolonged lactational amenorrhea. Although infants should still be managed individually so that insufficient growth or other adverse outcomes are not ignored and appropriate interventions are provided, the available evidence demonstrates no apparent risks in recommending, as a general policy, exclusive breastfeeding for the first six months of life in both developing and developed country settings. Large randomized trials are recommended in both types of setting to rule out small effects on growth and to confirm the reported health benefits of exclusive breastfeeding for six months or beyond.

J Nutr. 2001 Feb.
Effects of exclusive breastfeeding for four versus six months on maternal nutritional status and infant motor development: results of two randomized trials in Honduras.
Dewey KG, Cohen RJ, Brown KH, Rivera LL.
Department of Nutrition and Program in International Nutrition, University of California, Davis, California, USA.

To examine whether the duration of exclusive breastfeeding affects maternal nutrition or infant motor development, we examined data from two studies in Honduras: the first with 141 infants of low-income primiparous women and the second with 119 term, low birth weight infants. In both studies, infants were exclusively breastfed for 4 mo and then randomly assigned to continue exclusive breastfeeding (EBF) until 6 mo or to receive high-quality, hygienic solid foods (SF) in addition to breast milk between 4 and 6 mo. Maternal weight loss between 4 and 6 mo was significantly greater in the exclusive breastfeeding group (EBF) group than in the group(s) given solid foods (SF) in study 1 (-0.7 +/- 1.5 versus -0.1 +/- 1.7 kg, P < 0.05) but not in study 2. The estimated average additional nutritional burden of continuing to exclusively breastfeed until 6 mo was small, representing only 0.1-6.0% of the recommended dietary allowance for energy, vitamin A, calcium and iron. Women in the EBF group were more likely to be amenorrheic at 6 mo than women in the SF group, which conserves nutrients such as iron. In both studies, few women (10-11%) were thin (body mass index <19 kg/m(2)), so the additional weight loss in the EBF group in study 1 was unlikely to have been detrimental. Infants in the EBF group crawled sooner (both studies) and were more likely to be walking by 12 mo (study 1) than infants in the SF group. Taken together with our previous findings, these results indicate that the advantages of exclusive breastfeeding during this interval appear to outweigh any potential disadvantages in this setting.

BMJ. 1990 Jan 6.
Protective effect of breast feeding against infection.
Howie PW, Forsyth JS, Ogston SA, Clark A, Florey CD.
Ninewells Hospital and Medical School, Dundee.

Objective: To assess the relations between breast feeding and infant illness in the first two years of life with particular reference to gastrointestinal disease. Design: Prospective observational study of mothers and babies followed up for 24 months after birth. Setting: Community setting in Dundee. Patients: 750 pairs of mothers and infants, 76 of whom were excluded because the babies were preterm (less than 38 weeks), low birth weight (less than 2500 g), or treated in special care for more than 48 hours. Of the remaining cohort of 674, 618 were followed up for two years. Interventions: Detailed observations of infant feeding and illness were made at two weeks, and one, two, three, four, five, six, nine, 12, 15, 18, 21, and 24 months by health visitors. Main outcome measure: The prevalence of gastrointestinal disease in infants during follow up. Results: After confounding variables were corrected for, babies who were breast fed for 13 weeks or more (227) had significantly less gastrointestinal illness than those who were bottle fed from birth (267) at ages 0-13 weeks (p less than 0.01; 95% confidence interval for reduction in incidence 6.6% to 16.8%), 14-26 weeks (p less than 0.01), 27-39 weeks (p less than 0.05), and 40-52 weeks (p less than 0.05). This reduction in illness was found whether or not supplements were introduced before 13 weeks, was maintained beyond the period of breast feeding itself, and was accompanied by a reduction in the rate of hospital admission. By contrast, babies who were breast fed for less than 13 weeks (180) had rates of gastrointestinal illness similar to those observed in bottle fed babies. Smaller reductions in the rates of respiratory illness were observed at ages 0-13 and 40-52 weeks (p less than 0.05) in babies who were breast fed for more than 13 weeks. There was no consistent protective effect of breast feeding against ear, eye, mouth, or skin infections, infantile colic, eczema, or nappy rash. Conclusion: Breast feeding during the first 13 weeks of life confers protection against gastrointestinal illness that persists beyond the period of breast feeding itself.

PIP: The hypothesis that breastfeeding has a protective effect on the incidence of childhood illnesses in the 1st 2 years of life, particularly gastrointestinal disease, was investigated in a prospective study of 618 Scottish infants. Detailed observations of infant feeding practices and sickness episodes were made at 2 weeks and 1, 2, 3, 4, 5, 6, 9, 12, 15, 18, 21, and 24 months of age by health visitors. Of the 674 mother-infant pairs originally enrolled in the study, 267 bottle-fed from birth, 180 breastfed but weaned before their infant was 13 weeks of age, and 227 breastfed for 13 weeks or more (97 of these women exclusively breastfed their infants for the 1st 13 weeks of life). During the 1st 13 weeks, the adjusted rate (corrected for social class, maternal age, and parental smoking) for gastrointestinal illness was 2.9% among fully breastfed and 5.1% among partially breastfed infants compared with 15.7% among bottle-fed infants and 16.7% among weaned infants. In addition, the rate of respiratory illness was significantly greater in bottle-fed infants (37.0%) compared with partially (24.2%) and fully (25.6%) breastfed infants. In the period beyond the 1st 13 weeks of life, infants who had been partially or fully breastfed initially had significantly lower rates of gastrointestinal disease at 14-26 weeks, 27-39 weeks, and 40-52 weeks compared to bottle-fed infants and a lower rate of hospital admission. Although brief breastfeeding (less than 13 weeks) did not confer significant protection against disease, infants who were breastfed 13-26 weeks had as much subsequent protection as those breastfed for longer durations.

Soc Sci Med. 1990.
The place of the clock in pediatric advice: rationales, cultural themes, and impediments to breastfeeding.
Millard AV.
Department of Anthropology, Michigan State University, East Lansing.

This analysis treats the U.S. medical literature as evidence concerning the formal system of knowledge in allopathic medicine. An examination of pediatric advice on breastfeeding reveals the logic of medical reasoning, the use of scientific rationales, and the intrusion of specific cultural themes. The corpus of data includes works of 18 authors published in 36 volumes from 1897 to 1987, 27 volumes being editions of two major pediatric textbooks. All sources advocate breastfeeding but the detailed advice on how to carry out the process actually tends to undermine it. Moreover, the clock has provided the main frame of reference, creating regimentation reminiscent of factory work, segmenting breastfeeding into a series of steps, and emphasizing efficiency in time and motion. Feeding schedules were advocated in former decades as a matter of discipline for the infant, but nowadays they are viewed as biologically innate to normal infants and to breast milk production. The literature manifests responses over the century to behavioral, biochemical and physiological studies; however, except possibly for one textbook, no thorough rethinking has occurred. Sources of the 1980s continue to focus on the tempo of feeding as a major concern. Cultural themes besides the factory model of breastfeeding include the extension of professional advice to family matters, the subordination of lay women to professional expertise, mistrust of women's bodily signals including the let-down reflex in determining the timing of feedings, mistrust of signals from infants as well, and a professional ideal of flexible advice coupled with rigid limits concerning schedules. The literature interweaves the cultural themes with rationales based on physiological studies in support of specific regimens in breastfeeding, and the relegation of control in breastfeeding to medical experts denies the validity of mutual bodily and emotional responses within the mother-infant dyad. Pediatric authorities thus participate in the selection of cultural themes emphasized in motherhood. Although the pediatric literature is not the only influence on physicians and women, it reinforces pressures on women regarding their orientations toward their infants and hence, may be expected to shape our views of infancy, motherhood, and humanity in general. The break from the bindings of schedules has been proclaimed at various points during the century; however, the clock ironically remains the major reference point in most pediatric sources today.

Isr J Med Sci. 1984 May.
Episodes of illness in breast-fed and bottle-fed infants in Jerusalem.
Palti H, Mansbach I, Pridan H, Adler B, Palti Z.

In a prospective study on breast-feeding in Jerusalem, 274 middle-class Jewish women were interviewed about their breast-feeding practices, and symptoms and signs of disease, episodes of illness and hospitalization of the infant. Women of a higher education level breast-fed more often and for a longer period than did women with less education. Infants exclusively breast-fed had significantly fewer symptoms of disease than did those not breast-fed or partially breast-fed. The odds ratios for cough, respiratory difficulty, and diarrhea by breast-feeding practice were 3.66, 2.14 and 2.72 (P = 0.04). Significant differences in the number of illness episodes were found between breast-fed and bottle-fed infants at 20 weeks; infants exclusively breast-fed had the least number of illness episodes. A positive association was found between number of illness episodes and duration of breast-feeding. Infants who were breast-fed for 20 weeks had the least number of illness episodes; 52% of them had no episode compared with only 15% who were not breast-fed. Comparison of the numbers of illness episodes among non-breast-fed infants of mothers with low and high education levels indicated that the infants of better educated mothers had a significantly lower percentage of illness episodes (P less than 0.05). Even infants of a middle-class and well-educated population benefit from the breast-feeding practice and its protective effect, more so if they are exclusively breast-fed and for a longer period.

PIP: The frequency of illness episodes in bottlefed, partially breastfed, and exclusively breastfed infants was compared through the 19th postpartum week for 274 infants born at the Hadassah University Hospital between January and July 1979. 402 infants were selected for inclusion in the study from the 1000 consecutive births, which occurred at the hospital during that time period, on the basis of residential proximity to the hospital and single birth status. Mothers of the infants were interviewed after delivery, just prior to discharge, at 6-7 weeks postpartum, and at 20 weeks postpartum. 69% of the mothers were interviewed at all 4 stages, and 274 were interviewed at the 4th stage. At each stage the women were questioned about infant feeding practices and at the 3rd and 4th stage about illness episodes among their infants. 50% of the mothers were Israeli born, 31% were of European or American origin, and the remaining 19% were either from [Asia] or North Africa. 52% had more than 12 years of schooling, and 48% had less. 89% of the women started breastfeeding in the hospital, 41% still breastfed at 13 weeks, and 27% still breastfed at the 20th week. Prolonged breastfeeding was more common among the more educated mothers than among the less educated mothers. At 20 weeks postpartum the mothers were asked whether their infants experienced any of 10 symptoms during the previous week. Infants exclusively breastfed at 20 weeks had significantly fewer symptoms than partially breastfed and bottlefed infants. For example the proportion of infants who had more than 1 symptom was 8% for the exclusively breastfed, 43% for the partially breastfed, and 43% for the bottlefed infants. Odds ratios for the bottlefed infants compared to the breastfed infants for respiratory difficulties, cough, diarrhea, and vomiting were respectively 3.66, 2.14, 2.72, and 2.14. When educational level was controlled, the corresponding values were 3.33, 1.96, 2.27, and 1.49. An analysis of the number of illness episodes which occurred between the 6th and 20th postpartum weeks revealed that exclusively breastfed infants had significantly fewer episodes than the other 2 groups of infants. For example, the proportion of infants who had 3 or more illness episodes was 16% for bottlfed infants, 4% for partially breastfed infants, and 0% for exclusively breastfed infants; and the proportion reporting no episodes of illness was 62% for the exclusively breastfed, 47% for the partially breastfed, and 29% for the bottlefed. The pattern held for all educational groups and was strongest for infants whose mothers had the least education. Furthermore, 11% of the bottlefed, 8.1% of the partially breastfed, and 2.7% of the exclusively breastfed infants required hospitalization at some point between the 1st and 20th postpartum week. These findings demonstrate that even in predominantly middle class populations, breastfeeding provides health advantages for infants.