Francesca Giuffrida

Human milk (HM) is dynamic and shows a high inter- and intra-individual variability. To characterize HM with precision, it is necessary to understand the factors that modulate its composition. The objective of this narrative review is to summarize the maternal, infant and methodological factors that affect HM composition. We searched SCOPUS and PubMed databases for articles related to factors that are known to or could potentially influence HM composition and volume across lactation periods. Our comprehensive review encompasses various maternal-, infant-related, and methodological factors that modulate aspects of HM composition including macro- and micronutrients, vitamins and minerals, as well as volume. The most profound changes were observed in HM lipids and lipophiles. Evidence exists for many of the infant-related factors known to affect the nutritive and non-nutritive components of HM (e.g., birth weight, gestational age, infant age/stage of lactation). In contrast, less is known with respect to maternal factors; where there is either limited research or conflicting evidence (e.g., maternal lifestyle, obstetric history, medical conditions), except for the mother's diet, for which there is a relatively well-established understanding. Equally, although many of the methodological factors (e.g., HM sampling, handling and analytics) are known to impact HM composition, few studies have investigated this as a primary outcome, making it an important area of future research in HM. Here we propose a systematic capture of numerous maternal- and infant-related characteristics to facilitate associative comparisons of HM data within and across studies. Additionally, it would be prudent to standardize the methodological aspects known to affect HM composition in analytics, not only for HM lipids and lipophiles, but also for those nutrients whose variability is yet less well-understood. Defining the factors determining HM composition with accuracy will open perspectives for maternal intervention to optimize milk composition for specific needs of infants.

BACKGROUND: A recent report suggested that human milk (HM) composition not only changes with lactation stages but also vary according to gender of the offspring. In spite of available literature, the dynamic changes of HM composition still remain to be completely explored and characterized. Progress in analytical technologies together with quantitative sampling of HM allows for a better quantification of HM nutrients and thereby providing a deeper understanding of the dynamics of HM secretion. OBJECTIVE: To characterize and quantify HM nutrients based on appropriate for analyses sampling procedures and advanced analytical methodologies. CLINICAL STUDY DESIGN: We conducted an observatory, single center, longitudinal trial with HM collection at 30, 60, and 120 days postpartum from 50 mothers (singleton-deliveries of 25 male and 25 female infants). HM samples were analyzed for lipid, lactose, energy density, fatty acids, phospholipids, and gangliosides. Longitudinal analyses of the datasets have been carried out using linear mixed models. RESULTS: HM for male infants compared to females at 120 days, were higher for energy content and lipids by 24 and 39%, respectively. Similarly, other bioactive lipids such as linoleic acid, phospholipids and gangliosides were also significantly different based on the gender of the infant. Significant stage-based differences were observed for total lipids, energy density, phospholipids, and gangliosides. Such difference in HM composition may stem from different energy needs to cope up for individual growth and development. CONCLUSION: Collectively, the current observations affirm that HM secretion, especially the lipid composition, is a very dynamic and personalized biological process.