Effect of breastfeeding on infant and child mortality due to infectious diseases in less developed countries: a pooled analysis. WHO Collaborative Study Team on the Role of Breastfeeding on the Prevention of Infant Mortality.

BACKGROUND: The debate on breastfeeding in areas of high HIV prevalence has led to the development of simulation models that attempt to assess the risks and benefits associated with breastfeeding. An essential element of these simulations is the extent to which breastfeeding protects against infant and child mortality; however, few studies are available on this topic. We did a pooled analysis of studies that assessed the effect of not breastfeeding on the risk of death due to infectious diseases.
METHODS: Studies were identified through consultations with experts in international health, and from a MEDLINE search for 1980-98. Using meta-analytical techniques, we assessed the protective effect of breastfeeding according to the age and sex of the infant, the cause of death, and the educational status of the mother.
FINDINGS: We identified eight studies, data from six of which were available (from Brazil, The Gambia, Ghana, Pakistan, the Philippines, and Senegal). These studies provided information on 1223 deaths of children under two years of age. In the African studies, virtually all babies were breastfed well into the second year of life, making it impossible to include them in the analyses of infant mortality. On the basis of the other three studies, protection provided by breastmilk declined steadily with age during infancy (pooled odds ratios: 5.8 [95% CI 3.4-9.8] for infants <2 months of age, 4.1 [2.7-6.4] for 2-3-month-olds, 2.6 [1.6-3.9] for 4-5-month-olds, 1.8 [1.2-2.8] for 6-8-month-olds, and 1.4 [0.8-2.6] for 9-11-month-olds). In the first 6 months of life, protection against diarrhoea was substantially greater (odds ratio 6.1 [4.1-9.0]) than against deaths due to acute respiratory infections (2.4 [1.6-3.5]). However, for infants aged 6-11 months, similar levels of protection were observed (1.9 [1.2-3.1] and 2.5 [1.4-4.6], respectively). For second-year deaths, the pooled odds ratios from five studies ranged between 1.6 and 2.1. Protection was highest when maternal education was low.
INTERPRETATION: These results may help shape policy decisions about feeding choices in the face of the HIV epidemic. Of particular relevance is the need to account for declining levels of protection with age in infancy, the continued protection afforded during the second year of life, and the question of the safety of breastmilk substitutes in families of low socioeconomic status.