Trace elements status in human breast milk of mothers from Île-de-France region

Breastfeeding is the main source of nutrition during first months of life. Its composition varies according to parameters like mother's diet and health, living area, number of pregnancies and lactation duration… Trace-elements concentration in breastmilk is then an important parameter that can affect infant's health, growth or immune system and organ functions. Few data are available on this topic, and results are often very variable. The aim of this work is to determine reference values of Copper (Cu), Zinc (Zn), Selenium (Se), Cobalt (Co), Iron (Fe) and Iodine (I) in human breastmilk according to lactation duration and to study influencing parameters on its elementary composition. Regional Human Milk Bank of Necker Enfants Malades Hospital provided samples that came from breastfeeding woman involved in voluntary milk donation and epidemiologic data. Two hundred thirty-two breastmilk were analysed. After nitric acid mineralization of milk samples, Cu, Zn, Se, Co and I were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) in a standard mode. Fe was measured by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Both assays were validated in terms of sensitivity, repeatability and accuracy.Studied breast milks came from mothers with an average age of 32 years and donation time ranged from one day after childbirth to 974 days (> 2.5 years); mean lactation duration is 59 days (> 8 weeks) while median duration is 29 days (around 4 weeks). In all studied samples, mean results and reference values are for Cu: 6.02 (1.71-13.23), Zn: 43.86 (7.3-107.0), Se: 0.12 (0.07-0.24), I: 0.29 (0.07-1.01) and Fe: 4.72 (1.25-11.49) µmol/L and for Co: 12.28 (5.27-25.82) nmol/L. Important number of studied milks allowed their distribution into seven classes of lactation durations. Samples were divided into four successive classes of fifteen days after childbirth, two other classes corresponding to the 3rd and 4th months and a last class for milks sampled after 4 months of lactation. Results were analysed in each class allowing study of evolution during lactation. That was particularly interesting for Zn, that presented an important variability in the total population (4-132 µmol/L) explained by variation along lactation evolution decreasing from 48 to 17 µmol/L in first and last duration classes respectively. In addition, Cu and Fe concentrations were also significantly correlated with lactation duration while Se and I were in a lesser extent (p = 0.002). In this study, we present reference values for studied trace elements at different lactation stages, allowing a fine interpretation of future breast milk samples results according to their sampling time. By continuing this study, we plan to increase number of samples in some of the classes and to study the influence of premature birth or twin pregnancy on breast milk elementary composition.