Maternal selenium status influences the concentration and binding pattern of zinc in human milk

To study the health effects of high dietary maternal selenium intake breast milk, blood and toe-nails were collected from 143 women (20-24 days of lactation) living in Venezuelan states of Yaracuy and Portuguesa. Depending on the regional selenium intake level three regions were defined within the total range of 90-980 microgram per day. The samples were analyzed by means of INAA for the determination of trace elements, including selenium and zinc. The significant inverse correlation between Se and Zn in breast milk found in former studies was confirmed. Investigation of the Zn-binding pattern in milk whey was carried out by an on-line combination HPLC (SEC) for protein separation and ICP-AES for element detection. Six Zn-binding compounds including citrate were detected. A highly significant negative correlation was found between the citrate, which is the main low-molecular Zn-binding compound, and the maternal daily selenium intake. We determined that the decrease in zinc concentration is due to a decrease in the citrate level, which depends on the selenium concentration in breast milk. The selenium concentration in breast milk is, in turn, proportional to the dietary intake. In addition, significant changes in the UV- and Zn-profiles were observed in the milk whey with the highest selenium content, indicating that above a certain maternal intake level substantial changes in the composition of mammary secretory cells occur. This effect can be of interest for estimation of the safe dietary intake level of selenium.