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