Maternal influences on the glucocorticoid concentrations of human milk: The STEPS study

Human milk (HM) contains a wide array of non-nutritive bioactive elements, including glucocorticoid hormones (glucocorticoid; cortisol and cortisone). The relationship between milk-borne glucocorticoids, measures of maternal health and patterns of breast-feeding is not yet established. This study was conducted to determine the influence of maternal and infant related biological and socio-demographic factors on the levels of glucocorticoids hormones in HM.

Samples were obtained from lactating mothers (n = 656) participating in the Finnish cohort the STEPS study (Steps to the Healthy Development and Well-being of Children) when the infants were 11.29 (±2.6) weeks of age. Glucocorticoids (both cortisol and cortisone) concentrations were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Maternal demographics, biological and social factors were obtained using hospital records and self-reported diaries and questionnaires.

The majority of women reported that they were exclusively breastfeeding at the time of sample donation (51.2%). For all collected samples, cortisone (9.55 ± 3.44 ng/ml) was the predominant hormone and cortisol (7.39 ± 5.97 ng/ml) was present in all samples. Strong and positive correlation was found between cortisol and cortisone (r = 0.60, p=<0.0001). Cortisone was statistically different between overweight, normal and underweight women (p = 0.01) for cortisol no difference was seen (p = 0.96). Whilst, preterm birth (born before 37 week gestation) was positively associated with both cortisol (p = 0.04) and cortisone (p = 0.01). There was also a significant but weaker negative relationship between mothers educational status and cortisol (p = 0.05) and no effect was seen for cortisone (p = 0.82). Interestingly, no significant differences was found in glucocorticoid concentrations between exclusive and partial breastfeeding women.

HM contains glucocorticoids hormones. The concentrations are influenced by the varying maternal factors including maternal weight, preterm birth and maternal educational status, suggesting the possible role of maternal biological and social influences on milk hormonal composition. Interestingly, there was no influence of feeding patterns on HM glucocorticoids. Further analysis is required to fully explore the relationship with measures of maternal stress, including mother's glucocorticoid status.