Global Update

Indian Pediatrics 2001; 38: 565-567  

The Optimal Duration of Exclusive Breastfeeding: Results of a WHO Systematic Review

Appropriate feeding practices are of fundamental importance for the survival, growth, development, health and nutrition of infants and children everywhere. In this light, the optimal duration of exclusive breastfeeding is one of the crucial public health issues that WHO keeps under continual review. ‘There has long been consensus on the need for exclusive breast-feeding; however, there has been considerable debate on its optimal duration.

In view of the continuing debate, early in 2000, WHO commissioned a systematic review of the published scientific literature on the optimal duration of exclusive breastfeeding; more than 3000 references were identified for independent review and evaluation. The outcome of this process was subjected to a global peer review, after which all findings were submitted for technical scrutiny during an expert consultation (Geneva, 28 to 30 March 2001).

The duration of exclusive breastfeeding, and the timely introduction of adequate, safe and appropriate complementary foods in conjunction with continued breastfeeding, are of direct relevance for much of WHO’s work concerning infants and young children. This includes two major global initiatives currently under way: (i) a multi-country study, involving more than 10,000 children, whose aim is to establish a new international growth reference that reflects growth pattems of healthy breast-fed infants and children, thereby establishing the normative model against which all alternative feeding methods must be measured in terms of growth, health and development; and (ii) the development of a global strategy on infant and young child feeding, whose aim is to ensure adequate, safe and appropriate feeding for all infants and young children.

The results of the systematic review, together with information concerning develop-ment of the global strategy for infant and young child feeding, will be reported to the Fifty-fourth World Health Assembly in May 2001. The expert consultation’s conclusions, and recommendations for both practice and research, are as below:

A systematic review of current scientific evidence on the optimal duration of exclusive breastfeeding identified and summarized studies comparing exclusive breastfeeding for 4 to 6 months, versus 6 months, in terms of growth, infant iron status, morbidity, atopic disease, motor development, postpartum weight loss, and amenorrhea. It should be noted that the review was based on two small controlled trials and 17 observational studies that varied in both quality and geographic provenance.

The evidence does not suggest an adverse effect of exclusive breastfeeding for 6 months on infant growth on an overall population basis, i.e., on average. The sample sizes were insufficient, however, to rule out an increased risk of growth faltering in sonic infants who are exclusively breastfed for 6 months, particularly in populations with severe maternal mal-nutrition and a high prevalence of intrauterine growth retardation. The evidence from one trial in Honduras demonstrates poorer iron status in infants exclusively breastfed for 6 months, versus 4 months followed by partial breast-feeding to 6 months, and this evidence is likely to apply to populations in which maternal iron status and infant endogenous stores are not optimal. The available evidence is grossly inadequate to assess risks of deficiency in other micronutrients.

The available data suggest exclusive breast-feeding for 6 months has protective effects against gastrointestinal infection. These data were derived from a setting (Belarus) where hygienically prepared complementary foods were used. The evidence does not demonstrate a protective effect against respiratory tract infection (including otitis media) or atopic disease, in infants exclusively breastfed for 6 months compared to infants exclusively breastfed for 4-6 months.

Because the data from the Honduras trials reporting more rapid motor development are inconsistent and susceptible to observer bias, they are insufficient to draw any inferences concerning neuromotor development. The results of two controlled trials in Honduras indicate that exclusive breastfeeding for 6 months (versus 4 months) confers an advantage in prolonging the duration of lactational amenorrhea in mothers who breastfeed frequently (mean 10-14 feedings/day). The same Honduran trials demonstrated higher postpartum weight loss in mothers who exclusively breastfed for 6 months compared with mothers who exclusively breastfed for 4 months.

In developing-country settings, the most important potential advantage of exclusive breastfeeding for 6 months - versus exclusive breastfeeding for 4 months followed by partial breastfeeding to 6 months-relates to infectious disease morbidity and mortality, especially that due to gastrointestinal infection (diarrheal disease). Because the evidence bearing directly on this issue was inadequate, however, the Expert Consultation also considered other published studies that did not meet the selection criteria for the systematic review. In particular, no mortality data were available that directly compared exclusive breastfeeding for 4-6 versus 6 months. Moreover, the morbidity data from developing countries were limited to the two Honduran trials, which had insufficient statistical power to detect any advantage of exclusive breastfeeding to 6 months, and which used hygienically prepared complementary foods. However, the strong protective effect against gastrointestinal infection observed in Belarus, coupled with the high incidence of and mortality from gastrointestinal infection in many developing country settings, leads us to infer that exclusive breastfeeding for 6 months would protect against diarrheal morbidity and mortality in such settings. This inference is further strengthened by morbidity data with relating to reduced risk of gastrointestinal infection and of all-cause mortality for exclusively breastfed children compared with partially breastfed infants from 4 to 6 months, regardless of when the latter stopped exclusive breastfeeding.

In summary, the Expert Consultation concludes that exclusive breastfeeding to 6 months confers several benefits on the infant and the mother. However, exclusive breast-feeding to 6 months can lead to iron deficiency in susceptible infants. In addition, the available data are insufficient to exclude several other potential risks with exclusive breastfeeding for 6 months, including growth faltering and other micronutrient deficiencies, in some infants. In all circumstances, these risks must be weighed against the benefits provided by exclusive breastfeeding, especially the potential reduc-tion in morbidity and mortality.

The Expert Consultation recommends exclusive breastfeeding for 6 months, with introduction of complementary foods and continued breastfeeding thereafter. This recommendation applies to populations. The Expert Consultation recognizes that some mothers will be unable to, or choose not to, follow this recommendation. These mothers should also be supported to optimize their infants’ nutrition.

The proportion of infants exclusively breastfed at 6 months can be maximized if potential problems are addressed: (i) The nutritional status of pregnant and lactating mothers; (ii) Micronutrient status of infants living in areas with high prevalence of deficiencies such as iron, zinc, and vitamin A; and (iii) The routine primary health care of individual infants, including assessment of growth and of clinical signs of micronutrient deficiencies.

The Expert Consultation also recognizes the need for complimentary feeding at 6 months of age and recommends the introduc-tion of nutritionally adequate, safe and appro-priate complementary foods, in conjunction with continued breastfeeding.

The Expert Consultation recognizes that exclusive breastfeeding to 6 months is still infrequent. However, it also notes that there have been substantial increases over time in several countries, particularly where lactation support is available. A prerequisite to the implementation of these recommendations is the provision of adequate social and nutritional support to lactating women.

There are a number of issues that are important for policy-making with regard to defining the optimal duration of exclusive breastfeeding and maximizing its benefits. The Expert Consultation recommends the following priority research areas: (i) A comparison of exclusive breastfeeding/predominant breast-feeding and partial breastfeeding for 4-6months on the following outcomes, to improve precision of estimates and their general applicability: proportion with growth faltering and malnutrition at six and twelve months, micronutrient status, diarrheal morbidity, neuromotor development, changes in maternal weight, lactational amenorrhea. Priority must be given to investigating these outcomes in infants born small-for-gestational-age or, alternatively, in those with low weight-for-age at four months; (ii) Assess breast-milk production and composition from mothers with a body mass index <18.5 and the adequacy of breast-milk for meeting infant requirements to six months; (iii) It is recognized that rates of exclusive breastfeeding decline substantially after four months. ldentify biological and social constraints to exclusive breastfeeding to six months in different geographical and cultural settings, and develop appropriate and effective interventions to deal with these barriers and their consequences; (iv) Use available oppor-tunities to gain greater insight into the impact on mortality of exclusive breastfeeding to six months (for example, incorporate additional variables in the Demographic and Health Surveys); (iv) Develop and evaluate inter-ventions for micronutrient supplementation and for complementary foods in different areas of the world. This would include formative studies to identify processing and preparation methods, and local ingredients required to prepare nutritionally adequate, safe and appropriate complementary foods; (v) Assess the role of care during pregnancy and its effect on the adequacy of lactation in the first six months.