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DRI Dietary Reference Intakes: For Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline
reported in Australia (Andrews et al., 1967), Missouri (Hurwitz et al., 1997), Scandinavia (Johnsen et al., 1991), and Boston (Krasinski et al., 1986). In the general elderly population, many cases of atrophic gastritis may remain undiagnosed.
Testing of individuals who have low serum B12 values but who do not have pernicious anemia reveals a substantial proportion with malabsorption of protein-bound B12 (Carmel et al., 1987, 1988; Jones et al., 1987). More importantly, Carmel and coworkers (1988) found that 60 percent of those with neurological, cerebral, or psychological abnormalities malabsorbed food-bound B12. Food-bound malabsorption is found in persons with certain gastric dysfunctions (e.g., hypochlorhydria or achlorhydria with an intact stomach, post-gastric surgery such as Billroth I or II, and postvagotomy with pyloroplasty) and in some persons with initially unexplained low serum B12 (Carmel et al., 1988; Doscherholmen et al., 1983). Suter and colleagues (1991) reported that subjects with atrophic gastritis absorb significantly less B12 than do healthy control subjects but that the difference disappears after antibiotic therapy.
Miller and colleagues (1992) studied the absorption of radiolabeled B12 in patients who had not had gastric surgery but who had low B12 values. All patients with elevated serum gastrin levels absorbed food-bound B12 poorly compared with 21 percent of all those with normal serum gastrin values. In this study normal values were specified as greater than 12 percent absorption of food-bound B12 and greater than 33 percent absorption of free B12 as measured by direct body radioactivity measurements. Control subjects with normal serum B12 values (median 173 pmol/L [234 pg/mL], range 125 to 284 pmol/L [170 to 385 pg/mL]) absorbed 12 to 39 percent of food-bound B12 and 54 to 97 percent of free B12 (median 75 percent). The median age of this group was 61 years (range 49 to 69 years). Available evidence does not indicate that aging or atrophic gastritis increases the amount of B12 that must actually be absorbed to meet the body’s needs.
The high cyanide intake that occurs with cigarette smoking may disturb the metabolism of B12. In a study of healthy adults (Linnell et al., 1968), mean urinary B12 excretion was significantly higher in the 16 smokers than in the 16 nonsmokers (81.2 ± 8.7 [standard