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

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 dur ing 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 4 0 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 sa mples were collected shortly after. Milk fractionation was performed by ult racentrifugation, gel-column chromatography, and thin-layer chromatography. Concentrations of selenium were analyzed using atomic absorption spectroph otometry and glutathione-peroxidase by spectrophotometry. Concentrations of selenium in milk and plasma and content of proteins in milk were significa ntly 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 wit h those of total proteins, casein, and whey. In general, these parameters i ncluding the activity of glutathione-peroxidase, were decreased as lactatio n was prolonged. The major chemical form of selenium in human milk was foun d 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 moth ers may reflect the high protein content of regional diets and traditional treatment with herbal medicines during post-parturition and 3) selenomethio nine is the major selenium-containing compound located in the whey protein fraction of human milk, and this may enhance the bio-availability of seleni um. J. Trace Elem. Exp. Med. 14:57-67. 2001. (C) 2001 Wiley-Liss, Inc.