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The optimal duration of exclusive breastfeeding – and thus the optimal timing of when complementary feeding should begin – is an important public health issue. Therefore in 2000, WHO commissioned a systematic review of the published scientific literature on the optimal duration of exclusive breastfeeding. The outcome of this process was peer reviewed, then all findings were scrutinized during an expert consultation which took place in March 2001 in Geneva.
Based on the results of the systematic review, the 54th World Health Assembly held in May 2001 endorsed the recommendation that infants should be exclusively breastfed for the first six months of life. Thereafter, to meet their evolving nutritional requirements, infants should receive nutritionally adequate and safe complementary foods while breastfeeding continues for up to two years of age or beyond.
Background
In 1995 WHO published the report of the WHO Expert Committee on physical status; this included a meticulous review of available scientific evidence, including the Organisation's own research, on the influence of exclusive and non-exclusive breastfeeding patterns on the growth of infants and children in a number of countries in disparate regions. The evidence showed that, in predominantly breastfed infants, weight and growth velocity begin to fall at 3 months of age when judged against the current NCHS/WHO reference. In contrast, weight and growth velocity begin to fall at about 5 months of age when judged against a trial breastfed growth reference. This suggested that whatever the underlying cause (e.g. inadequate nutrient supply, infection) nutrient intake in predominantly breastfed infants may become insufficient to meet their normal growth requirements from about 5 months of age (or even earlier, depending on the growth reference used). It was also clear that there was considerable variation in the age at which this insufficiency occurred. On this basis the WHO Expert Committee and its Working Group on Infant Growth:
- reconfirmed the suitability of WHO's current recommended timing of the introduction of complementary foods – that is, 4–6 months of age; and
- urged that a new growth reference be developed based on breastfed infants who are living under conditions that favour achievement of genetic growth potential.
Given the worldwide variation in growth velocity and other health and development outcomes, an age range is an essential element of WHO's population–based infant feeding recommendation. Since the publication of the Expert Committee's findings in 1995, there have been a number of additional studies and reviews, including a WHO–commissioned scientific review on complementary feeding (document WHO/NUT/98.1), a randomized intervention study in Honduras (Cohen et al., The Lancet 1994;343;288-93), and several other recent studies and reviews (e.g. Werk & Alpert, The Lancet 1998;352:1569 and The WHO Collaborative Study Team on the Role of Breastfeeding on the Prevention of Infant Mortality, The Lancet 2000;355:451-55).
In order to ensure that it’s infant feeding recommendation continues to reflect the most up-to-date globally applicable scientific and epidemiological evidence, WHO commissioned a systematic review of the published scientific literature on the optimal duration of exclusive breastfeeding as well as a multicentre study, among other things, contributing to improved understanding of the age range during which breast milk alone is sufficient to meet the healthy infant's nutritional requirements.
Expert consultation on the optimal duration of exclusive breastfeeding
(extract from the WHO “Note for the Press N°7, 2 April 2001”)
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 some infants who are exclusively breastfed for 6 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 6 months, versus 4 months followed by partial breastfeeding 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 breastfeeding 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 (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 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 diarrhoeal 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 breastfeeding 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 reduction in morbidity and mortality.
RECOMMENDATIONS FOR PRACTICE
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:
- The nutritional status of pregnant and lactating mothers.
- Micronutrient status of infants living in areas with high prevalence of deficiencies such as iron, zinc, and vitamin A.
- 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 complementary feeding at 6 months of age and recommends the introduction of nutritionally adequate, safe and appropriate 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.
The WHO Multicentre Growth Reference Study
The WHO multi-country study involved approximately 8500 children from geographically and ethnically diverse sites (Brazil, Ghana, India, Norway, Oman and the USA). The study combined a longitudinal component from birth to 24 months with a cross-sectional study from 18 to 71 months. The aim was to establish a new international growth reference that reflects growth patterns of healthy breastfed infants and children living in environments that do not constrain growth. The new reference establishes the breastfed infant as the normative model against which all alternative-feeding methods must be measured in terms of growth, health and development. The prospective follow-up from birth to 24 months, involving 1800 infants, included assessments at fortnightly intervals from birth to 2 months, and monthly from 3-12 months of age, of breastfeeding and complementary feeding patterns; anthropometry; and health, morbidity, mortality and other indicators.
The WHO Child Growth Standards that were derived from the data collected in the WHO Multicentre Growth Reference Study are all available on the WHO website, along with application tools to support implementation of the standards
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