Human milk: nutritional aspects of a dynamic food.

The composition and volume of human milk progressively changes with the onset and duration of lactation and can be influenced by maternal nutritional factors. Current evidence indicates that infant demand is the major determinant of the quantity of milk transferred to the nursing infant. Human milk is remarkable for its variability, and ranges of intakes of milk constituents are comparable with normal patterns of infant growth and development. Lipids are by far the most variable constituents in human milk with both long-term maternal nutrition states and daily intake capable of exerting an influence. Maternal vitamin intake bears a strong relationship to milk content, and appropriate intakes of vitamins D and K may not always be furnished to nursing infants. Major and trace minerals in human milk are not greatly affected by maternal diet, with selenium and iodine being notable exceptions. Compartmentalization and molecular forms of the trace elements in human milk are associated with high infant bioavailability. The success of lactation should be measured using maternal and infant indices of nutritional adequacy.