Determination of selenium concentration and its chemical forms in the milk of Kuwaiti and non-Kuwaiti lactating mothers

Abstract

The objectives of the present study were to compare the selenium status in the milk and plasma of Kuwaiti mothers with that of non-Kuwaiti mothers during 0–18 months of lactation and to identify and compare the chemical forms of selenium in human milk and cow milk. Thirty-four donors between 25 to 40 years of age (Kuwaitis, n = 17; non-Kuwaitis, n = 17) were studied. Milk samples were obtained prior to the first feeding of the infant and blood samples were collected shortly after. Milk fractionation was performed by ultracentrifugation, gel-column chromatography, and thin-layer chromatography. Concentrations of selenium were analyzed using atomic absorption spectrophotometry and glutathione-peroxidase by spectrophotometry. Concentrations of selenium in milk and plasma and content of proteins in milk were significantly higher in the Kuwaiti group than those of the non-Kuwaitis during the first 12 months of lactation. The selenium profile in milk was parallel with those of total proteins, casein, and whey. In general, these parameters including the activity of glutathione-peroxidase, were decreased as lactation was prolonged. The major chemical form of selenium in human milk was found to be selenomethionine. Cow milk did not appear to contain this compound, but might have a free selenium form that is neither selenite nor selenate. In conclusion, 1) the higher level of selenium in the milk of Kuwaiti mothers may reflect the high protein content of regional diets and traditional treatment with herbal medicines during post-parturition and 2) selenomethionine is the major selenium-containing compound located in the whey protein fraction of human milk, and this may enhance the bio-availability of selenium. J. Trace Elem. Exp. Med. 14:57–67, 2001. © 2001 Wiley-Liss, Inc.