are formula fed. In general, this pattern is not altered by the introduction of solid foods. Differences in linear growth between breastfed and formula-fed infants are small if statistical techniques are used to control differences in size at birth.

Infant Morbidity and Mortality

Several types of health problems occur less often or appear to have less serious consequences in breastfed than in formula-fed infants. These include certain infectious diseases (especially ones involving the intestinal and respiratory tracts), food allergies, and, perhaps, certain chronic diseases. There is suggestive evidence that severe maternal malnutrition might reduce the degree of immune protection afforded by human milk, but further studies will be required to address that issue.

Few infectious agents are commonly transmitted to the infant via human milk. The most prominent ones are cytomegalovirus in all populations that have been studied and human T lymphocytotropic virus type 1 (HTLV-1) in certain Asian populations. The transmission of cytomegalovirus by breastfeeding does not result in disease; the consequences of the transmission of HTLV-1 by breastfeeding are unknown. There are some case reports that indicate that human immunodeficiency virus (HIV) can be transmitted by breastfeeding as a result of the transfusion of HIV-contaminated blood during the immediate postpartum period. The likelihood of transmitting HIV via breastfeeding by women who tested seropositive for the agent during pregnancy has not been determined. Public policy on this issue has ranged from the Centers for Disease Control's recommendation not to breastfeed under these circumstances to the World Health Organization's encouragement to breastfeed, especially among women in developing countries.

In developing countries, mortality rates are lower among breastfed infants than among those who are formula fed. It is not known whether this advantage also holds in industrialized countries, in which death rates are lower in general. It is reasonable to believe that breastfeeding will lead to lower mortality among disadvantaged groups in industrialized countries if they have higher than usual infant and child mortality rates, but this issue has not been studied.

Medications, Drugs, and Environmental Contaminants

The few prescription drugs that are contraindicated during lactation because of potential harm to the infant can usually be avoided and replaced with safer acceptable ones. For example, there are a number of safe and effective substitutes for the antibiotic chloramphenicol, which is contraindicated for lactating women. If treatment with antimetabolites or radiotherapeutics is required by the mother, breastfeeding is contraindicated.

Cigarette smoking and alcohol consumption by lactating women in excess

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