of 0.5 g/kg of maternal weight may be harmful to the infant, partly because of potential reduction in milk volume. Furthermore, a single report (Little et al., 1989) associates heavy alcohol use by the mother with retarded psychomotor development of the infant at 1 year of age. Infrequent cigarette smoking, occasional consumption of small amounts of alcohol, and moderate ingestion of caffeine-containing products are not considered to be contraindicated during breastfeeding. Use of illicit drugs is contraindicated because of the potential for drug transfer through the milk as well as hazards to the mother. Since the limited information on the impact of these habits upon the nutrition of women in the childbearing years is reviewed in Nutrition During Pregnancy (IOM, 1990), they were not considered further by this subcommittee.
In the uncommon situation of a high risk of exposure to such environmental contaminants as organochlorinated compounds (such as dichlorodiphenyl-trichloroethane [DDT] or polychlorinated biphenyls [PCBs]) or toxic metals (such as mercury), risks must be weighed against the benefits of breastfeeding for both mother and infant on a case-by-case basis. In areas of unusually high exposure, levels of the contaminant should be measured in the mother's blood and milk.
Breastfeeding substantially increases the mother's requirements for most nutrients. The magnitude of the total increase is most strongly affected by the extent and duration of lactation. Adequacy of intakes of calcium, magnesium, zinc, folate, and vitamin B6 merits special attention since average intakes may be below those recommended. The net long-term effect of lactation on bone mass is uncertain. Some data associate lactation with short-term bone loss, whereas most recent studies suggest a protective long-term effect. Those data are provocative but of such preliminary nature that no definitive conclusions may be drawn from them.
Although most lactating women lose weight gradually during lactation, some do not. The influence of lactation on long-term postpartum weight retention and maternal risk of adult-onset obesity has not been determined.
A well-documented effect of lactation is delayed return to ovulation. In addition, some recent epidemiologic evidence indicates that breastfeeding may lessen the risk that the mother will develop breast cancer, but the data are not consistent across all studies.
The major conclusions of the report are as follows.
Women living under a wide variety of circumstances in the United