Abstract
There is strong evidence that breastfeeding protects infants against infection in environments where clean water cannot be guaranteed, leading to substantial reductions in morbidity and mortality. This is particularly evident in the protection against gastrointestinal disease, although there is also evidence for protection against respiratory infection and otitis media. The evidence for a protective effect of breastfeeding against infection in developed countries has been more controversial, with criticisms being levelled at the methodology of many studies. Evidence is presented from a study in a developed country that met key methodological criteria to show that breastfeeding for 13 weeks offers substantial and continuing protection against gastrointestinal illness. Smaller, but still potentially important, protective effects against respiratory illness also occur. The results add strong support to policies that promote breastfeeding in both developed and developing countries.