Conclusions and recommendations (Geneva, 28 to 30 March 2001)

A systematic review of current scientific evidence on the optimal duration of exclusive breastfeeding 2 identified and summarized studies that compared exclusive breastfeeding for four to six months with exclusive breastfeeding for six months in terms of growth, infant iron status, morbidity, atopic disease, motor development, postpartum weight loss, and amenorrhoea. It should be noted that the review was based on two small controlled trials and 17 observational studies that varied in both quality and geographical provenance.

The evidence does not suggest an adverse effect of exclusive breastfeeding for six months on infant growth on an overall population basis, that is on average. The sample sizes were insufficient, however, to rule out an increased risk of growth faltering in some infants who are exclusively breastfed for six months, particularly in populations with severe maternal malnutrition and a high prevalence of intrauterine growth retardation.

The evidence from one trial in Honduras demonstrates poorer iron status in infants exclusively breastfed for six months than in infants exclusively breastfed for four months followed by partial breastfeeding to six months. This finding is likely to apply to populations in which maternal iron status and infant endogenous stores of iron are not optimal. The available evidence is grossly inadequate to assess risks of deficiency of other micronutrients.

The available data suggest that exclusive breastfeeding for six 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 six months compared to those exclusively breastfed for four to six months.

The Expert Consultation recommends exclusive breastfeeding for six months, with introduction of complementary foods and continued breastfeeding thereafter. This recommendation applies to populations."

Because the data from the Honduran trials that reported more rapid motor development are inconsistent and susceptible to observer bias, they are insufficient to allow any inferences to be drawn about neuromotor development.

The results of two controlled trials in Honduras indicate that exclusive breastfeeding for six months (compared with four months) confers an advantage in prolonging the duration of lactational amenorrhoea in mothers who breastfeed frequently (mean 10-14 feedings/day).

These recommendations form the findings of the Expert Consultation mandated by the WHO Secretariat and reported to the 54th World Health Assembly in May 2001. Because the definition of "exclusive breastfeeding" in studies in the systematic review often included infants who were predominantly breastfed, the term is used here to include both true exclusive breastfeeding and predominant breastfeeding, as defined by WHO.

The same Honduran trials demonstrated greater postpartum weight loss in mothers who exclusively breastfed for six months compared with mothers who exclusively breastfed for four months.

In developing-country settings, the most important potential advantage of exclusive breastfeeding for six months over exclusive breastfeeding for four months followed by partial breastfeeding to six months relates to infectious disease morbidity and mortality, especially those due to gastrointestinal infection (diarrhoeal 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 four to six with that for six 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 six 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, led the experts at the consultation to infer that exclusive breastfeeding for six months would protect against diarrhoeal morbidity and mortality in such settings. This inference is further strengthened by morbidity data relating to reduced risks of gastrointestinal infection and of all-cause mortality for exclusively breastfed children compared with partially breastfed infants from four to six months, regardless of when the latter stopped exclusive breastfeeding.

The Expert Consultation recognizes that some mothers will be unable to, or choose not to, follow this recommendation; they should be supported to optimise their infants' nutrition."

In summary, the Expert Consultation concludes that exclusive breastfeeding to six months confers several benefits on the infant and the mother. However, exclusive breastfeeding to six months can lead to iron deficiency in susceptible infants. In addition, the available data are insufficient to exclude several other potential risks associated with exclusive breastfeeding for six 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 reduction in morbidity and mortality.

Recommendations for practice

The Expert Consultation recommends exclusive breastfeeding for six 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; they should be supported to optimise their infants' nutrition.

The Expert Consultation recognizes the need for complementary feeding at six months of age and recommends the introduction of nutritionally adequate, safe and appropriate complementary foods, in conjunction with continued breastfeeding.

The Expert Consultation also recognizes that exclusive breastfeeding to six 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.

Recommendations for research

There are several unanswered questions that are important for policy-making with regard to defining the optimal duration of exclusive breastfeeding and maximizing its benefits. Therefore, the Expert Consultation recommends that priority be given to the following research areas: