Submitted to: Journal of Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/30/2003
Publication Date: 1/1/2004
Citation: Etcheverry, P., Miller, D.D., Glahn, R.P. 2004. A low molecular weight factor in human milk whey promotes iron uptake by caco-2 cells. Journal of Nutrition. 134(1):93-98. Interpretive Summary: We have applied a simulated intestinal digestion/cell culture model to study the effects of the major milk components (fat, whey and casein) from human milk and cow's milk on Fe bioavailability. Regarding human milk, the results showed that removing the whey component decreased Fe bioavailability, thus indicating that the whey fraction contains promoters of Fe uptake. Removal of the fat fraction increased Fe uptake, indicating that this component has a negative effect on Fe bioavailability. Removal of the casein component had no effect on Fe uptake. In cow's milk, removal of whey and or fat had no effect on Fe uptake; whereas removal of the casein fraction increased Fe uptake, indicating that the casein of cow milk is an Fe uptake inhibitor. The results of cow milk are consistent with those previously described in the literature. The human milk study represents a novel approach that could yield information as to precise factors promoting Fe uptake from human milk.
Technical Abstract: Iron bioavailability from human milk (HM) is substantially higher than from cow milk (CM) but the factor responsible for this high bioavailability is unknown. The purpose of this study was to evaluate the effects of various HM and CM fractions on iron bioavailability. Ultracentrifugation was used to separate milk into casein, fat and whey fractions. Whey was further fractionated by ultrafiltration using a 10 kDa membrane to produce a 10k retentate (10kR) and a 10k filtrate (10kF). Samples were prepared by mixing various combinations of the fractions, bringing to pre-fractionation weights with MEM, and adding iron (10 umol/L) as ferrous sulfate. Samples were divided into 2 aliquots and one was subjected to in vitro digestion, the other was not. Bioavailability was assessed by applying the samples to monolayers of Caco-2 cells and incubating for 24 h. Ferritin formation in the cells was used as an index of iron uptake. In undigested samples, removal of fat from HM caused a doubling of ferritin formation but removal of whey or casein had no effect. Similar results were obtained with digested HM samples except that removal of whey decreased ferritin formation by 48%. In CM, removal of fat had no effect but removal of casein resulted in a doubling of ferritin formation (in digested samples). Removal of the 10kF from HM reduced ferritin by 60% but removal of the 10kR had no effect. These data suggest that a low molecular weight factor (<10kDa) in human milk is an iron absorption enhancer.