Overview
There is good evidence
that breast feeding reduces the rate of gastrointestinal and respiratory
infections and that this effect is found even in developed countries. In
addition, in infants who have a family history of atopy, breast feeding
in conjunction with restricted maternal diet during pregnancy and lactation
may reduce the incidence of atopic illness in their children. Finally,
numerous case-control studies have observed that those with insulin-dependent
diabetes were either not breast fed or were breast fed for a shorter duration
than controls without the disease.
There is good evidence for implementation of a number of peripartum maneuvers such as rooming-in of newborns with their mothers, early and frequent physical contact, and banning of the provision of commercial samples to encourage the duration of breast feeding. Both antepartum and postpartum counselling prolong breast feeding duration. The effect of supplemental bottles of formula or water on duration of breast feeding remains unclear.
Burden of
Suffering
For the purpose of this paper,
breast feeding refers to exclusive breast feeding unless otherwise stated.
Rates of breast feeding in one-week- old infants in the U.S. increased
from 29% in 1955
to 52% in 1989.<1>
This increase, however, reached a peak in 1982
when 62% of infants were breast fed at age one week. This pattern is matched
by rates of breast feeding at 5-6 months which rose from 5% in 1971
to
28% in 1984
and fell to 18%
in 1989.
Certain groups are at greater risk of not breast feeding, including young
mothers and those in lower socioeconomic groups, particularly those receiving
social insurance benefits.<2> Data from the Ross Database on breast
feeding in Canada show overall rates of breast feeding initiation of 75%
among 3 cohorts born in 1991
and
1992 (personal
communication, Anne Dumas, Manager, Nutrition Services, Ross Laboratories).
Fifty-four percent and 30% were still breast feeding at 3 and 6 months
of age, respectively. Lower rates were observed in Quebec and the Maritimes
and higher rates in British Columbia.
Effectiveness of Breast Feeding in Prevention of Adverse Outcomes
Infections
In their critical review of
the literature, Bauchner and colleagues<3> concluded that there was
no definitive evidence in developed countries that breast feeding reduced
infections, since those studies of the highest methodologic quality did
not find any differences. Since that review, three cohort studies have
met the stringent methodologic requirements set forth by these authors.
In a British study,<4> 750 mother-infant pairs were seen at home on thirteen occasions during the first 24 months of life. Health visitors administered a questionnaire detailing feeding method as well as illness history in the intervening period between visits. Maternal education, maternal age, and smoking history, which were the only factors predicting infections were included in a multiple regression model. Breast feeding for a period beyond thirteen weeks was independently protective for gastrointestinal infections, and to a lesser extent, respiratory infections. Four percent of 227 infants who were breast feeding at this time vs. 15.7% of infants who were bottle feeding had experienced a gastrointestinal infection. A significantly lower proportion had been hospitalized for their infection – 2% of those breast feeding more than 13 weeks vs. 7.7% of those who never breast fed had been hospitalized in the first year. Twenty-six percent of breast vs. 37% of bottle feeding infants experienced respiratory infections. A similar reduction in respiratory illness hospitalizations was observed but the difference did not reach statistical significance. The effect of breast feeding persisted beyond the period of breast feeding and occurred despite supplementation.
In another cohort study conducted in Denmark, monthly questionnaires were sent to the home for self-administration to ascertain feeding methods and infections.<5> 500 patients were enrolled, but only 44% were followed for the full 12 months of the study. No protection against infection was afforded by breast feeding in this study. This may have been due to a lower overall rate of infection in this largely middle-class population, the inclusion of partial along with exclusive breast feeding in the breast feeding group, the use of self-administered monthly questionnaires, or incomplete follow-up of patients.
Compared with exclusive or supplementary bottle feeding, exclusive breast feeding for four months or more was found in the third study to protect against both acute and recurrent otitis media.<6> Healthy infants enrolled at birth were followed for the occurrence of acute and recurrent otitis media diagnosed by their physicians during the first year of life. Infants exclusively breast fed during the first 4 months of life had a 0.72 and 0.54 odds of developing acute and recurrent otitis media respectively, compared with those who were exclusively bottle fed or received breast milk for less than 6 months. A dose-response effect was observed in that infants who received supplementation in addition to breast feeding had intermediate infection rates.
In summary, two well-conducted cohort studies provide evidence supporting protection against gastroenteric and respiratory infections and otitis media. Thus, there is grade II-2 evidence in support of protection against infection through breast feeding.
Atopy
The studies which relate breast
feeding to protection against atopic disease are not of high quality. Kramer
critically reviewed the literature up to 1986
and concluded that methodologic limitations of the available studies prevented
conclusions about any protective effect of breast feeding.<7> Notably,
women who belong to higher socioeconomic classes have higher rates of atopic
children and are more likely to breast feed, so the bias would be to reduce
observed benefits for breast feeding if adjustment for social class did
not take place.<7> Similarly, concerns regarding atopy in their offspring
may cause more atopic women to breast feed, also reducing benefits observed
from breast feeding in research studies.
Several cohort studies and a single randomized controlled trial in preterm infants have not found any significant benefit of breast feeding compared with bottle feeding on the onset of atopy.<8-10> However, in those at increased risk of atopy as defined by a positive family history or positive cord immunoglobulin E (IgE), breast feeding may prevent atopy.<11> Similarly in a subgroup of 160 preterm infants involved in a randomized trial comparing breast milk with two lactose-based formulas, there was a 3.6 fold odds of atopy in those receiving formula.<10>
One cohort study and two trials of maternal dietary restriction in conjunction with breast feeding also observed benefit in those receiving the intervention.<12-14> Because of the lack of blinding in the cohort study, its conclusions are limited. However, there was a halving of the incidence of atopy in the two trials in the treatment arm compared with the control arm. It is not possible to separate the relative contribution of antenatal dietary restriction from the effect of avoidance of certain foods during lactation to the outcome. In addition, problems with the dietary restriction resulted in low compliance in one of the studies and only those who complied with the intervention were included in the final analysis.<14>
In summary, breast feeding does not appear to alter the development of atopy in the general population. However, poor study power and short duration of breast feeding in some studies weaken the evidence. One cohort study and several trials have suggested that restricting maternal diets during breast feeding may reduce the incidence of atopy in their children. Thus, exclusion of various foods from the diet of breast feeding mothers may be useful in a subpopulation at increased risk of atopy (positive family history or markers such as increased cord IgE).
Insulin-dependent Diabetes
Mellitus
Numerous case-control studies
have observed either a lower frequency or shorter duration of breast feeding
in patients developing diabetes compared with population or sibling controls.
This protection from diabetes through breast feeding has been shown even
after adjusting for differences in potential confounders such as socioeconomic
status. This effect may be due to immunologic properties of breast milk
or alternatively to delayed exposure to cow’s milk.<15>
One group hypothesized that antibody directed to a component of bovine
serum albumin not found in human or murine albumin cross-reacts with a
pancreatic beta-cell receptor.<16>
They observed significantly higher levels of this antibody among newly
diagnosed diabetics compared with an age-, gender- and region-matched control
group.<16>
Thus, there is fair evidence to support the role of breast feeding in preventing diabetes, particularly in a subgroup with genetic markers indicating an increased risk of diabetes.<17,18> For more information on diabetes mellitus consult Chapters 2 and 50 (pregnant and non-pregnant adults, respectively).
Growth and Development
Studies with limited power
have reported no difference in either skin fold thickness or weights in
infants fed different formulas compared with breast milk. However, a cohort
study of infants matched for family socioeconomic status, ethnicity, birth
weight, gender, and time of introduction of solids reported a significantly
higher mean weight in the first eighteen months among those receiving formula.
Whether this difference suggests that formula-fed infants are overweight
or that breast-feeding protects against subsequent obesity is unclear.
It is, therefore, not possible to conclude which is the better diet since
the most desirable outcomes have not been defined.
Studies examining maternal bonding (parent-infant attachment) and breast feeding are inconclusive since they do not adjust for major confounders that affect choice of feeding method and bonding. Cohort studies linking breast milk feeding to increased intelligence quotients also need replication. However, some evidence of this type including the benefits of breast feeding are included in the next Chapter on iron deficiency anemia in infants (Chapter 23).
Efficacy of
Interventions to Encourage Breast Feeding
In a meta-analysis Renfrew<19>
found that, based on two studies of antenatal breast feeding education,
the odds of discontinuing breast feeding at one to two months was significantly
reduced at 0.2. A single trial of antenatal breast feeding classes versus
individual teaching did not show any consistent differences in breast feeding.<20>
In a meta-analysis of six trials, a significant benefit was observed for
postnatal support.<21>
The pooled odds ratio of 0.75 (95% confidence interval (CI): 0.62-0.91)
for stopping breast feeding before 8-12
weeks despite differences in the nature of this support.
A randomized controlled trial involving primiparas has observed prolonged duration of breast feeding from a median of 77 days in a control group allowed to nurse four to six hours after delivery and every 4 hours thereafter to 182 days in the group who breast fed within 10 minutes of delivery and every two hours thereafter.<22> A group receiving only early initiation appeared to have a longer duration of breast feeding than a group with delayed onset but frequent breast feeding in the peripartum period. In a Canadian randomized trial of early contact compared with the control group, 9 of 15 mothers who had early contact with their infants were still exclusively nursing their infants compared with 3 of 15 control mothers (Fisher’s exact test, p<0.001).<23> Two other studies also indicate that early contact prolongs breast feeding – the first used systematic allocation based on birth week and the second used true random allocation.<24,25> Although the direction of improvement was towards the early contact group, the differences did not reach statistical significance, possibly because only a small number of subjects had complete follow-up. Another randomized trial of 78 subjects did not observe a benefit of early mother-infant contact on duration of breast feeding.<26> However, randomization was not successful since more women intending to breast feed were in the group receiving early contact vs. routine contact, the population involved advantaged women who were already likely to breast feed and might therefore show less improvement with the intervention, and follow-up involved only 50 subjects thus severely limiting power. Combining the data from all studies of early contact compared with a control group shows a significant increase in breast feeding as measured at the different observation periods.
Another potential method for increasing breast feeding is the avoidance of bottle supplementation. There are two theories as to why bottle supplementation may discourage breast feeding. The first is that bottle feeding is mechanically easier than breast feeding. The second is that the perception that their milk supply is inadequate may be reinforced in mothers who observe their infants nursing from a bottle. However, conflicting results have been reported from a cohort study, a quasi-experimental study and a randomized trial. Differences in patient population and intervention make the evidence regarding bottle supplementation difficult to interpret.
Two well designed randomized trials suggest that provision of formula samples prior to discharge reduces the proportion of infants still being breast fed at either three or four months after discharge.<27,28> In both studies, using a Cox analysis, the effect of providing formula samples was seen within two months of birth.
From these studies, one can conclude that peripartum practices that enhance breast feeding include unrestricted contact between mother and baby following delivery, encouragement of demand feeding, and avoidance of giving formula samples to parents at discharge. However, there is poor compliance with these practices in English and Canadian maternity hospitals.<29,30>
Care must be taken to ensure hydration in breast fed babies since breast feeding leads to greater weight loss during the early postnatal period compared with bottle feeding, presumably due to inadequate fluid intake. Dehydration coupled with inadequate stooling may result in jaundice.
Viruses, including cytomegaloviruses (CMV), hepatitis B, HIV, and HTLV-1, have been isolated from breast milk and may cause infections in the newborn. The significance of breast milk transmission of CMV during the neonatal period is unclear. With universal immunization against hepatitis B, the incremental increase in transmission of this virus is likely to be minimal. However, the threat of HIV infection has led to discouragement of breast feeding by HIV-infected mothers in developed countries. It would be reasonable to consider maternal screening programs for HIV infection (as discussed in Chapter 58).
Guilt or other negative impacts may occur in women who are being told that ‘breast is best’ but are unable to either initiate or sustain breast feeding. Of women who had discontinued breast feeding prior to 12 weeks, two-thirds admitted feeling upset or guilty at having stopped.<31>
Recommendations
of Others
Both the American Academy
of Pediatrics and the Canadian Pediatric Society have recommended breast
feeding as the preferred mode of infant feeding.<32> Their recommendations
include public education programs, encouragement of breast feeding during
prenatal care as well as on maternity wards, and examination of feasibility
of breast feeding in day care centres adjacent to places of work.
The World Health Organization and UNICEF have developed explicit guidelines to encourage breast feeding around the world.<33> They incorporate the peripartum practices described above.
Conclusions
and Recommendations
There is level II-2 evidence
indicating that breast feeding will reduce morbidity related to infectious
illnesses in developed countries. In subgroups at high risk of atopy, randomized
trials suggest that breast feeding in conjunction with restriction of the
mother’s diet during pregnancy and lactation may reduce the incidence of
atopy in the baby. Case-control studies have observed a higher incidence
of lack of breast feeding or shorter duration of breast feeding in patients
with insulin-dependent diabetes mellitus compared with controls. Given
the evidence for benefit of breast feeding in the prevention of several
adverse outcomes and that this is the strongest evidence that can ethically
be obtaining for causation, breast feeding should be recommended as the
preferred method of infant feeding. Based on meta-analysis of randomized
trials of counselling, there is good evidence to support antenatal and
postnatal counselling (A Recommendation).
Trials dealing with the peripartum environment also support a recommendation for early frequent contact and rooming-in privileges as well as banning provision of free formula samples (A Recommendation). The evidence for avoidance of bottle supplementation in the peripartum period is contradictory and inconclusive.
Unanswered
Questions (Research Agenda)
The following have been identified
as research priorities:
This review was initiated in June 1993 and recommendations were finalized by the Task Force in January 1994.
Acknowledgements
The Task Force thanks Michael
S. Kramer, MD, Peds (P.Q.), Professor of Pediatrics and of Epidemiology
and Biostatistics, McGill University, Montreal, Quebec; Ms. Marie Labreche,
Reg N, Program Officer, Family and Child Health, Health Promotion Directorate,
Health Canada, Ottawa, Ontario; and Stanley H. Zlotkin, MD, PhD, FRCPC
(Peds), Associate Professor of Pediatrics and Nutritional Sciences, University
of Toronto, Toronto, Ontario for reviewing the draft report. Funding for
this report was provided by Health Canada under the Government of Canada’s
Brighter Futures Initiative.
Full Citation
Wang E.E.L. Breast feeding. In: Canadian Task
Force on the Periodic Health Examination. Canadian
Guide to Clinical Preventive Health Care. Ottawa: Health Canada,
1994; 232-42.