Elsevier

Early Human Development

Volume 86, Issue 11, November 2010, Pages 729-732
Early Human Development

“Breast is best”: The evidence

https://doi.org/10.1016/j.earlhumdev.2010.08.005Get rights and content

Abstract

Although the benefits of breastfeeding in reducing morbidity and mortality from gastrointestinal and respiratory infections, sudden infant death syndrome, and (in preterm infants) necrotizing enterocolitis are well-established, long-term health effects are more controversial. The evidence is conflicting concerning the “programming” effect of breastfeeding in protecting against child obesity, hyperlipidemia, hypertension, type 2 diabetes, and atopic disease. Accelerated neurocognitive development has been associated with breastfeeding in many studies, although doubts remain about the potential for residual confounding due to cognitive and behavioural differences between mothers who breastfeed (or those who breastfeed for a longer duration or more exclusively) and those who do not. Most of this paper will summarize the methods and results of a large, cluster-randomized trial of a breastfeeding promotion intervention in the Republic of Belarus. Its experimental design and intention-to-treat analysis have yielded important findings bearing on several of these longer-term health and developmental outcomes.

Introduction

Breastfeeding has been consistently associated with reduced short-term morbidity and mortality from gastrointestinal and respiratory infections, the sudden infant death syndrome, and (in preterm infants) necrotizing enterocolitis [1]. The protection against infection has been shown to persist into the second and even third years of life in developing countries, where it is associated with significant reductions in mortality [2], [3]. But even in developed countries, where common infections are rarely fatal, a protective effect is well-established [1].

All the above-mentioned effects appear to be limited to the actual period of breastfeeding, rather than a carry-over, or “programming,” effect over the long-term. In contrast, in recent years breastfeeding has also been studied with respect to its potential effect on longer-term health during childhood and even in adulthood. Protective effects have been reported against obesity [4], [5], hyperlipidemia [6], hypertension [7], insulin resistance and type 2 diabetes [8], atopic disease (including atopic eczema, asthma, hay fever, and positive skin tests) [9], [10], and even against other, rarer diseases with a presumed immunologic basis, such as type 1 diabetes, inflammatory bowel disease, leukemia, and lymphoma [1]. Finally, breastfeeding has also been associated with improved cognitive ability [11], although given that much brain development occurs during the period of infant feeding, it is not clear whether such an effect represents an acute effect (with delayed measurement of the outcome) or a true “programming” effect.

For the long-term outcomes, virtually all of the evidence is based on observational studies. With respect to obesity, hypertension, and neurocognitive development, many concerns have been raised about the potential for bias due to residual confounding by differences in life-style, cognitive, and behavioural attributes of mothers who breastfeed and those who do not, and even between those who breastfeed more exclusively or for a longer duration and those who breastfeed less. For atopic outcomes, the problem is that no “gold standard” exists for the diagnosis of most allergic diseases. Not all children who wheeze have asthma, not all children who sneeze have hay fever, and not all children with recurrent itchy rash have eczema. Thus in prospective (cohort) studies, knowledge of infant feeding can bias how these diagnoses are made. Moreover, misclassification of infant feeding, which is a problem in all outcome studies based on different modes of infant feeding, is even more important for atopic outcomes, because issues of dose, immunologic tolerance, and timing of exposure to foreign antigens can theoretically all modify the relationship between exposure and outcome.

The best way of minimizing these multiple sources of bias is through the use of a randomized controlled trial (RCT) design. But randomization to breast vs artificial feeding is clearly infeasible and may even be unethical. What is feasible and ethical is to randomize women to a breastfeeding promotion intervention. In the remainder of this paper, I will describe the methods and results of such an RCT, which was designed to promote breastfeeding exclusivity and duration among Belarusian women who had decided to initiate breastfeeding, with analysis by intention-to-treat.

Section snippets

Methods

Our study is called the Promotion of Breastfeeding Intervention Trial (PROBIT). Details of PROBIT's design have been previously published [12], as have been the reports on outcomes during follow-up in the first year of life [12] and at age 6.5 years [13], [14], [15], [16], [17]. The experimental intervention used in PROBIT was based on the WHO/UNICEF Baby-Friendly Hospital Initiative [18], while the hospitals/clinics randomized to the control group were asked to maintain their usual care

Results

Table 1 compares baseline characteristics of the experimental and control groups at the time of randomization [12]. The comparison was very similar for those participating in the 6.5-year follow-up [13], [14], [15], [16], [17].

The audit results are summarized in Table 2. They show extremely high correlations for height, BMI, and waist circumference, intermediate correlations for triceps and subscapular skinfold thicknesses, but lower correlations for systolic and diastolic blood pressures. The

Discussion

To our knowledge, PROBIT is the largest randomized trial ever performed in the area of human lactation. Our results confirm previous observational evidence that prolonged and exclusive breastfeeding reduces the risk of gastrointestinal infection and atopic eczema during infancy. In contrast to many observational studies, however, we found no effect at the 6.5-year follow-up on stature or adiposity; no reduction in blood pressure, allergy or asthma, or dental caries; and no effect on behavior.

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