Fig. 3

Evaluation of the plausibility of milk hormones as signals between mother and offspring. To determine whether or not a hormone acts as a signal between mother and offspring, we suggest it is important to establish its source (whether from maternal blood or synthesised in the breast); whether milk concentrations are influenced by maternal/environmental factors; that milk hormones can reach the infant intestine and (probably) be absorbed; and that milk hormones influence infant outcomes. The figure summarises published data for each of these steps for leptin, adiponectin, ghrelin and cortisol and highlights the relative lack of consistent data for all stages of the pathway; most studies examine one or two components and few have examined infant outcomes beyond growth and/or adiposity. Furthermore, all studies are observational, precluding decisions on causality. R: rodent; S: sheep; C: cow