The content, binding, and forms of vitamin B12 in milk
1981
Sandberg, Diana P. | Begley, James A. | Hall, C. A. (Charles A)
The vitamin B12, or cobalamin, content of 19 human breast milk samples from nursing mothers 2-30 months postpartum ranged from 0.33-3.20 ng/ml (mean=0.97 ng/ml). Milk vitamin B12 content did not significantly differ between unsupplemented mothers and those taking 5-100 micrograms cyanocobalamin daily. Binding studies identified an unsaturated R type binder as the dominant protein binding cobalamin native to milk, although transcobalamin II (TC II) also was observed in every sample. TC II serum and milk levels were of the same order of magnitude; milk TC II levels increased with duration of lactation. Methylcobalamin was the dominant form of native cobalamin in the milk. Analysis revealed that human milk from well-nourished mothers contains adequate cobalamin. Vitamin bioavailability to the breastfed infant may depend, however, on levels of proteolytic enzymes needed to release the cobalamin from the R binder. (nm)
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