FREE AND PROTEIN-BOUND COBALAMIN ABSORPTION IN HEALTHY MIDDLE-AGED AND OLDER SUBJECTS

OBJECTIVE: To study free- and protein-bound cobalamin absorption and t he correlation with atrophic gastritis in healthy middle-aged and olde r subjects. DESIGN: A cross-sectional study. PARTICIPANTS: Fifty-two h ealthy subjects, aged 26 to 87 years, apparently free from conditions known to influence the cobalamin status. Middle-aged subjects were def ined as those younger than 65 years of age (median age 57 years) and o lder subjects as those 65 years and older (median age 75 years). MEASU REMENTS: Protein-bound cobalamin absorption was assessed by 48-hour ur inary 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 exc retion method following oral administration of crystalline Co-57-cyano cobalamin. Plasma cobalamin, folate and fasting plasma gastrin, and pe psinogen A and C concentrations were determined. RESULTS: The median u rinary excretion of egg yolk Co-57-cobalamin in middle-aged subjects w as 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). Th e median urinary excretion after administration of free Co-57-cobalami n in middle-aged subjects was 25.7% (25th and 75th percentiles 20.6%-3 0.7%) compared with 27.9% (25th and 75th percentiles 21.4%-34.5%) in o lder subjects (P = .694). Neither egg yolk nor free Co-57- cobalamin e xcretion 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 m oderate atrophic gastritis, and two subjects had a pepsinogen A concen tration less than 17 mu g/L, indicating severe atrophic gastritis or g astric atrophy. All subjects had normal fasting plasma gastrin concent rations. Free and egg yolk Co-57-cobalamin excretions were not reduced in the atrophic gastritis group when compared with the non-atrophic g astritis group. Median plasma cobalamin concentration was not signific antly lower in older subjects (P = .205). Nonetheless, plasma cobalami n concentration correlated negatively with age (r = -.36; P = .008). C ONCLUSIONS: We demonstrated no significant difference in either free o r protein-bound cobalamin absorption between healthy middle-aged and o lder adults. In addition, no alteration in cobalamin absorption was fo und in subjects identified as having mild to moderate atrophic gastrit is. Therefore, based on our results, the high prevalence of low cobala min levels in older people cannot be explained by either the aging pro cess or mild to moderate atrophic gastritis.