Breast milk selenocystine as a biomarker for selenium intake in lactating women at differential geographical deficiency risk in China.

BACKGROUND AND OBJECTIVES: A reliable biomarker for optimal selenium (Se) intake in lactating women is not currently available. METHODS AND STUDY DESIGN: Daily dietary Se intake in lactating women was calculated from a 24-hour meal record survey for over 3 days. Se levels in plasma and breast milk were measured through inductively coupled plasma mass spectrometry. Plasma selenoprotein P 1 levels and glutathione peroxidase 3 activity were measured using an enzyme-linked immunosorbent assay. Ultra-performance liquid chromatography-tandem mass spectrometry was used to analyze proteinaceous Se species in enzymatically digested breast milk. RESULTS: Dietary Se intakes of lactating women from Liangshan, Beijing, and Enshi were 41.6±21.2 ng/d, 51.1±22.6 ng/d, and 615±178 ng/d, respectively (p<0.05). The Se levels in the blood and breast milk were significantly associated with the dietary Se intake (p<0.05). The proteinaceous Se species in breast milk were SeMet and SeCys2. The levels of SeMet in the lactating women from Liangshan, Beijing, and Enshi were 3.31±2.44 ng Se/mL, 7.34±3.70 ng Se/mL, and 8.99±9.64 ng Se/mL, while that of SeCys2 were 13.7±12.0 ng Se/mL, 35.6±20.9 ng Se/mL, and 57.4±13.2 ng Se/mL, respectively. Notably, the concentration of SeCys2, the metabolite of unstable SeCys, reached a saturation platform, whereas no similar phenomenon were found for the total Se SeMet from Secontaining proteins. CONCLUSIONS: SeCys2 in breast milk is a potential biomarker for determining the optimal Se intake in lactating women.

Selenium in infant formula milk.

Formula-based animal milk is an alternative source of infant nutrition in many cases when breastfeeding is unacceptable or inaccessible; however, these replacements often have low selenium levels. The composition of infant formula milk should be as close as possible to that of human breast milk, both in content and chemical speciation. Selenium is an essential trace element for infants. Generally, human breast milk is the ideal food to ensure adequate infant Se intake. However, to date, sodium selenite or sodium selenate has been used as selenium supplementation in infant formula milk in most countries. This inorganic Se, which is not a natural component of food, may not be the optimal speciation for Se supplementation in infant formula milk. Advances in speciation in foods, especially in animal milk, suggest that future proposals for selenium speciation in human breast milk can lead to discussions regarding the most favorable methods of selenium supplementation in infant formula milk.