Bioavailability of vitamin B <inf>12</inf> in cows' milk
The natural source of vitamin B 12 in human diets comes from animal products. For example, one glass (250 ml) of milk provides approximately 50 % of the RDA (2•4 μg/d). It was hypothesised that the provision of vitamin B 12 from milk is more efficiently absorbed than the synthetic form used in vitamin supplements. Pigs (n 10) were used as a model for intestinal absorption of vitamin B 12 in humans to compare the net fluxes of vitamin B 12 across the portal-drained viscera (PDV; an indicator of intestinal absorption) after ingestion of meals complemented with conventional and vitamin B 12-enriched (via injections to cows) milk (raw, pasteurised or microfiltrated) or with equivalent amounts of cyanocobalamin, the synthetic form used in supplements or unsupplemented. Net flux of vitamin B 12 across PDV after the ingestion of milk was positive, though not influenced by milk enrichment (P>0•3) or technological processes (P = 0•8) and was greater than after ingestion of equivalent amounts of cyanocobalamin (cyanocobalamin v. all milk, P ≥ 0•003). In fact, net fluxes of this vitamin were not different from 0 after either cyanocobalamin or the meal devoid of vitamin B 12 (unsupplemented v. cyanocobalamin, P = 0•7). The cumulative PDV fluxes during the 24 h following ingestion of meals complemented with milk varied from 5•5 to 6•8 μg. These values correspond to an efficiency of intestinal absorption of vitamin B 12 from milk varying between 8 and 10 %. Therefore, vitamin B 12, which is abundant in cows' milk, is also substantially more available than the most commonly used synthetic form of this vitamin. © 2011 The Authors.
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