Variation of Human Milk Glucocorticoids over 24 hour Period
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Human milk (HM) contains a complex array of hormones, including members of the glucocorticoid family. The predominant glucocorticoids, cortisol and cortisone may influence the growth and behaviour of the breastfed infant. However, little is understood of the factors regulating the levels of these hormones within HM. The aim of the study was to examine HM cortisol and cortisone concentration, measured in samples collected at each feed during a 24 hour period. Twenty three exclusively breastfeeding mothers collected milk, prior to and after each breastfeeding session over 24 hour period at 3.2(1.60) months. HM cortisol and cortisone levels were measured using high pressure liquid chromatography mass spectroscopy. Cortisone was the predominant glucocorticoid (3.40 ng/ml), and cortisol was detected in all samples (1.62 ng/ml). A positive correlation was found between cortisone and cortisol (r = 0.61, y = 1.93 ± 0.24, p < 0.0001). Cortisol and cortisone concentrations were significantly higher in feeds in the morning (2.97 ng/ml and 4.88 ng/ml), compared to afternoon (1.20 ng/ml and 3.54 ng/ml), evening (0.69 ng/ml and 2.13 ng/ml) and night (1.59 and 3.27 ng/ml). No difference was found between glucocorticoids level of the milk expressed for collection either before or immediately after the breastfeed, or between milk collected from the left or right breast. This study shows that HM glucocorticoid concentrations exhibit a 24 hour pattern, with highest peak levels in the early morning, reflecting the circadian pattern as previously reported in plasma. Thus, HM glucocorticoid concentrations are likely to reflect those in the maternal circulation.
KeywordsGlucocorticoids Human milk Cortisol Cortisone High-performance liquid chromatography
Authors thank the research team and mothers for the kind donation of breast milk used in the current study.
S.P. carried out laboratory analysis and data interpretation and drafted manuscript. E.B.T developed the MS method and oversaw the laboratory work. C.R.W and C.J.M assisted with statistical analysis and contributed to the manuscript development. D.T.G and C.T.L provided samples and contributed to the manuscript development. D.C.S designed research question and supervised all aspects of the study. All authors approve the submission of this manuscript for peer review.
Compliance with Ethical Standards
This study was funded by the Liggins Institute, University of Auckland, Philanthropic trust, the Riddet Institute, Massey University.
Conflict of Interest
CRW is employed through, Faculty of Medical and Health Science, University of Auckland. CJM, EBT and DCS are employed through Liggins Institute, University of Auckland. CTL and DG receive a salary from an unrestricted research grant from Medela AG, administered by University of Western Australia.
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