VITAMIN B12 IN HUMAN COLOSTRUM AND MILK

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Abstract
The concentration of vitamin B12 was measured by microbiological assay in 229 samples of normal human colostrum and milk taken at various stages of lactation. Colostrum obtained within 48 h of delivery contains high concentrations of vitamin B12 (mean 2431 pg/ml) but within a few days the levels fall to a range similar to the levels in normal serum. The vitamin B12 binding capacity of 111 samples of colostrum and milk was estimated by gel filtration or charcoal binding. Colostrum samples have a mean binding capacity of 72 ng/ml while the binding capacity in milk is only 1/3 of this value. The ability of a range of intestinal bacteria to take up colostrum-bound vitamin B12 was assessed. All organisms took up free vitamin B12, but when the vitamin was bound in colostrum there was little or no uptake even after 24 h incubation.