Predictors of milk cortisol in North American women

Abstract

ObjectivesHuman milk content varies across mother–child dyads, environments, and populations. Among the hormones in milk is cortisol, a glucocorticoid; its impact on the breastfeeding child is unknown. Milk cortisol may constitute a signal to the child's developing physiology which can shape characteristics (e.g., growth, temperament) to prevailing environmental conditions. This exploratory study evaluated the maternal, breastfeeding, and infant characteristics associated with milk cortisol.MethodsWe evaluated archived milk specimens for cortisol using enzyme immunoassay and employed an information‐theoretic approach to assess associations between milk cortisol and participant characteristics with linear regression modeling. Because we employed secondary data, information for some variables likely to impact milk cortisol variation (e.g., time of day, socioeconomic status, maternal or infant body mass index, milk energy density) was unavailable.ResultsParticipants were 48 lactating mothers from upstate New York, aged 21–40 years. Milk cortisol ranged from 0.098 to 1.007 μg/dL. Child age ranged from 1 to 26 months. In linear regression employing best fit modeling criteria, milk cortisol increased with child age (B: 0.069; p: .000; a 7.1% increase in milk cortisol for each month of child age), while child symptoms of illness (B: −0.398; p: .057; a 33% decrease) and consumption of complementary foods (B: −.525; p: .020; a 41% decrease) were associated with lower milk cortisol.ConclusionsWe speculate that increasing milk cortisol with child age plays a role in signaling development (e.g., as increasing independence increases risk for injury and other negative health outcomes), independent of the maternal stressors we could capture.

Breast size in lactating women and the content of macronutrients in human milk

“…Additionally, maternal diet diversity (Caffé et al, 2023) and dietary intakes of proteins, carbohydrates, fats, and particularly fatty acids have been found to impact the content of breast milk macronutrients (Bravi et al, 2016; Keikha et al, 2017; Tian et al, 2019); however, not all studies confirm this relationship (Quinn et al, 2012). Finally, several studies have reported that milk composition may be associated with feeding frequency (Daly et al, 1993; Khan et al, 2013; Quinn et al, 2012), parity (Lindberg et al, 2021; Quinn et al, 2016), maternal age (Abdelhamid et al, 2020; Argov‐Argaman et al, 2016; Bachour et al, 2012; Dritsakou et al, 2017; Zhang et al, 2021), environmental conditions (Schafrank et al, 2020), and infant's age, size or health (Abdelhamid et al, 2020; Alderete et al, 2015; Anyim et al, 2023). The influence of the child's sex on the nutritional composition of milk is controversial.…”