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Investigation of holoTC, the active component of circulating vitamin B12, as a sensitive marker of dietary intake
Project Code: N05078
Trinity College Dublin (TCD)
Scott, J ; Molloy, A
Mild to moderate vitamin B12 deficiency is frequently present among older persons. Malabsorption of food-bound vitamin B12 due to atrophic gastritis is thought to be the most common reason for this. Underlying atrophic gastritis in a proportion of elderly subjects may also explain the poorer relationship between intake of vitamin B12 and blood vitamin B12 concentrations often seen in elderly compared to younger persons. We hypothesized that the blood concentration of holotranscobalamin (holoTC), which represents the fraction of serum vitamin B12 destined for tissue uptake, would be a more reliable marker of B12 status than the serum total vitamin B12 and would demonstrate a better association between intake and status. We further hypothesized that exclusion of those with atrophic gastritis would result in an even stronger correlation between intake and status for this vitamin. We proposed that these results would demonstrate a close relationship between vitamin B12 intake and status, apart from in a minority of the elderly with food-bound B12 malabsorption.
We conclude that holoTC is indeed a more sensitive and specific indicator of vitamin B12 status than the serum total vitamin B12 level and that the high prevalence of gastric atrophy among older persons contributes to a diminution in the association between intake and holoTC in this group. However, our results suggest that the relationship between B12 intake and total B12 status in elderly subjects may be more complex than generally assumed since removing subjects with gastric atrophy had virtually no effect on the relationship between intake and total vitamin B12 status. It is possible that changes in the haptocorrin bound fraction of B12 rather than the transcobalamin bound fraction underlie these differences. Further work is required in this area.
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