The potential physiological significance of milk-borne hormonally active substances for the neonate.

This article reviews the presence and potential physiological significance of hormones and hormonally active substances (including growth factors) in human milk. Human milk has been found to contain several nonpeptide hormones and many peptide hormones and growth factors. In contrast to human breast milk, infant formulae lack some hormonally active peptides. There is little data concerning the effects of these agents on human neonates. Studies in immature experimental animals showing effects of orogastically administered hormones are summarized. The problems of supplementation of infant formula are discussed. Since hormones are present in the milk as a "cocktail" of potentially agonistic and antagonistic substances, one question is whether supplementation with a single agent would disturb this balance.