Free and protein-bound cobalamin absorption in healthy middle-aged and older subjects

OBJECTIVE: To study free- and protein-bound cobalamin absorption and the correlation with atrophic gastritis in healthy middle-aged and older subjects. DESIGN: A cross-sectional study. PARTICIPANTS: Fifty-two healthy subjects, aged 26 to 87 years, apparently free from conditions known to influence the cobalamin status. Middle-aged subjects were defined as those younger than 65 years of age (median age 57 years) and older subjects as those 65 years and older (median age 75 years). MEASUREMENTS: Protein-bound cobalamin absorption was assessed by 48-hour urinary excretion method following oral administration of scrambled egg yolk, labeled in vivo with Co-57-cobalamin by injecting a hen with Co-57-cyanocobalamin. The percentage of Co-57-cobalamin bound to protein was 65%. Free cobalamin absorption was assessed by 48-hour urinary excretion method following oral administration of crystalline Co-57-cyanocobalamin. Plasma cobalamin, folate and fasting plasma gastrin, and pepsinogen A and C concentrations were determined. RESULTS: The median urinary excretion of egg yolk Co-57-cobalamin in middle-aged subjects was 12.3% (25th and 75th percentiles 10.5%-14.5%) compared with 11.7% (25th and 75th percentiles 9.8%-13.6%) in older subjects (P = .283). The median urinary excretion after administration of free Co-57-cobalamin in middle-aged subjects was 25.7% (25th and 75th percentiles 20.6%-30.7%) compared with 27.9% (25th and 75th percentiles 21.4%-34.5%) in older subjects (P = .694). Neither egg yolk nor free Co-57- cobalamin excretion correlated with age. A ratio of pepsinogen A to pepsinogen C less than 1.6, indicating atrophic gastritis, was found in 13 subjects. Within the atrophic gastritis group, 11 subjects had a pepsinogen A concentration greater than or equal to 17 mu g/L, indicating mild to moderate atrophic gastritis, and two subjects had a pepsinogen A concentration less than 17 mu g/L, indicating severe atrophic gastritis or gastric atrophy. All subjects had normal fasting plasma gastrin concentrations. Free and egg yolk Co-57-cobalamin excretions were not reduced in the atrophic gastritis group when compared with the non-atrophic gastritis group. Median plasma cobalamin concentration was not significantly lower in older subjects (P = .205). Nonetheless, plasma cobalamin concentration correlated negatively with age (r = -.36; P = .008). CONCLUSIONS: We demonstrated no significant difference in either free or protein-bound cobalamin absorption between healthy middle-aged and older adults. In addition, no alteration in cobalamin absorption was found in subjects identified as having mild to moderate atrophic gastritis. Therefore, based on our results, the high prevalence of low cobalamin levels in older people cannot be explained by either the aging process or mild to moderate atrophic gastritis.