The practicing clinician is faced with many issues when caring for an elderly person with potential B₁₂ deficiency. These issues include identifying patients at risk for deficiency, ordering and accurately interpreting laboratory measures of B₁₂ status and implementing appropriate treatment. As a guide for the generalist, this Cyberounds^® will review each of these issues.

Digestion and Absorption of Vitamin B12

Naturally occurring vitamin B₁₂ is bound to the food proteins for which it serves as a co-enzyme. Once in the stomach, acid and pepsin remove the food protein from the vitamin. The resulting free vitamin B₁₂ then binds to R binders, which are small proteins secreted by the stomach.

The R binder-vitamin B₁₂ complex then travels into the proximal small bowel, where the R proteins are separated from the B₁₂ by pancreatic proteases. It is here in the proximal small intestine, at a relatively neutral pH, that the vitamin B₁₂is free to bind to intrinsic factor, a small glycoprotein (also secreted by the stomach, but which does not bind to B₁₂ in the stomach because of the low pH environment). The vitamin B₁₂-intrinsic factor complex then migrates to the terminal ileum, where vitamin B₁₂ is actively absorbed.

Any interruption in this sequence of events diminishes vitamin B₁₂ bioavailability.

Etiologies and Evaluation of B12 Deficiency

Dietary inadequacy, atrophic gastritis and pernicious anemia are the most common causes vitamin B₁₂ deficiency in elderly people in the developed world.

Dietary Deficiency

Food sources of vitamin B₁₂ include meat, dairy products eggs, and cereals that have been fortified with vitamin B₁₂. An elderly person who does not consume sufficient quantities of these foods is at risk for vitamin B₁₂ deficiency.

Deficiency Caused By Atrophic Gastritis

A condition known as type B atrophic gastritis occurs in a large number of elderly people and is related to chronic Helicobacter pyloriinfection. In this condition, absorption of crystalline B₁₂ is normal but absorption of B₁₂ bound to food is diminished. In atrophic gastritis, secretion of stomach acid is reduced, decreasing the bioavailability of vitamin B₁₂ and, therefore, increasing its requirement. These abnormally low levels of stomach acid are unable to kill ingested bacteria, allowing them to proliferate in the stomach and small intestine.

In a study that compared a group of atrophic gastritis patients with a group of elderly people without atrophic gastritis, Suter and colleagues(1) confirmed that the absorption of crystalline vitamin B₁₂ is, in fact, normal in individuals with atrophic gastritis. However, they also found that absorption of protein-bound B₁₂ was abnormally lower in these subjects. This study also tested the ability of bacterial overgrowth to alter the bioavailability of vitamin B₁₂ in patients with atrophic gastritis. Administration of tetracycline restored protein-bound vitamin B₁₂ absorption to normal levels,(1) suggesting that bacteria in the proximal bowel play a role in decreasing the vitamin's bioavailability.

In vitro studies have demonstrated that small intestinal bacteria do not bind protein-bound vitamin B₁₂ but strongly bind crystalline vitamin B₁₂. It is believed that since acid-pepsin digestion is relatively impaired in atrophic gastritis, the concentration of free vitamin B₁₂ (that is, the B₁₂ that has been digested off of the food protein) is relatively low in the small intestine. The greater numbers of bacteria residing in atrophic gastritis subjects then take up the free, (crystalline) vitamin B₁₂, leading to the development of a vitamin B₁₂ deficiency. It is not known how frequently type B atrophic gastritis is responsible for low B₁₂ status in the elderly, although it has been estimated that one half of all cases result from this condition.

Deficiency Secondary to Pernicious Anemia

Pernicious anemia is the most common cause of clinically apparent vitamin B₁₂ deficiency in North American and European populations. Pernicious anemia is a disease state resulting from the complete lack of intrinsic factor as the result of severe, end-stage type A autoimmune chronic atrophic gastritis. Lack of intrinsic factor causes vitamin B₁₂ malabsorption, which, in turn, causes megaloblastic anemia as well as neurological and gastrointestinal manifestations of deficiency.

Type A chronic atrophic gastritis involves both the fundus and body of the stomach but spares the antrum. In contrast, type B (Helicobacter-related) gastritis principally involves the antrum of the stomach.

Autoantibodies to gastric parietal cells and to intrinsic factor are the cause of vitamin B₁₂ malabsorption in pernicious anemia. Gastric H+/K+-ATPase appears to be the target antigen of anti-parietal-cell autoantibodies. Parietal cells normally secrete hydrogen ions in exchange for potassium ions due to gastric H+/K+-ATPase. Parietal-cell autoantibodies bind to the alpha and beta sub-units of gastric H+/K+-ATPase, thereby causing destruction of the parietal cells in the gastric mucosa. The production of intrinsic factor is impaired by the progressive loss of parietal cells from the gastric mucosa. Further, anti-intrinsic-factor antibodies bind to the vitamin B₁₂ binding site of intrinsic factor, thus preventing the formation of the vitamin B₁₂-intrinsic factor complex.(2)

Clinical Presentation of Vitamin B₁₂ Deficiency

B₁₂ deficiency may present with hematologic manifestations, neurologic manifestations or both.

Hematologic Manifestations

Hematologic manifestations are characterized by megaloblastic anemia. Mean cell volume is increased and the erythrocytes are macroovalocytic. Neutropenia is frequently associated with hypersegmentation of neutrophils on a peripheral blood smear, defined as the presence of 5% or more of neutrophils containing 5 or more lobes, or 1 neutrophil having 6 lobes. Thrombocytopenia may also occur. The bone marrow is hypercellular in all cellular elements. The erythroid series in the bone marrow shows megaloblastic morphologic changes with a discrepancy in the maturity of nuclei versus cytoplasm (nuclear-cytoplasmic asynchrony). The nuclei are less mature than the cytoplasm and nuclear chromatin has a fine-grained texture.

Slowly developing anemia may cause skin pallor, fatigue, palpitations, dyspnea on exertion, headache and syncope.

Neurologic Manifestations

Elderly patients with vitamin B₁₂ deficiency may present with neurological or mental-status changes rather than megaloblastic anemia.(3),(4) This primary presentation of deficiency may be indirectly from higher folate levels in the diet, particularly since January 1997, when it was mandated that flour be fortified with folic acid.(5) Thus, the hematologic findings of vitamin B₁₂ deficiency may not be present despite a tissue deficiency of the vitamin - a condition formerly known as "masking of vitamin B₁₂ deficiency by folate."(6)

Seventy-five to ninety percent of individuals with clinically apparent vitamin B₁₂ deficiency display neurologic symptoms, which may arise from pathology in the spinal cord, peripheral nerves, cranial nerves or cerebrum. Symptoms often start with a symmetrical paresthesia and an impairment of vibration and position sense. These symptoms frequently progress to motor involvement, including gait abnormalities.(7) Personality changes, dementia, psychosis, depression and agitation may also occur. Such neurologic abnormalities may be irreversible if treatment is delayed, therefore all elderly individuals with any of these symptoms should be assessed for vitamin B₁₂ deficiency as early as possible.

Prevalence of Vitamin B₁₂ Deficiency

The prevalence of low vitamin B₁₂ status is estimated to be between 12% and 14% among independent people over the age of 60 and 25% among institutionalized elderly.(8),(9) In a survey of elderly people in Boston, about 24% of those over the age of 80 were found to have atrophic gastritis, using the accepted criteria of pepsinogen I : pepsinogen II ratio as a marker of this condition.(10)

The prevalence of B₁₂ deficiency from pernicious anemia is much lower. Carmel's 1996 survey(2) of 729 free-living individuals over 60 years old in Los Angeles revealed that 1.9% had undiagnosed pernicious anemia (low cobalamin concentration combined with an abnormal Schilling test or a positive anti-intrinsic factor antibody test). Further, the study of Krasinski et al.,(10) which employed 359 physically healthy Caucasian subjects older than 60 years, showed a similar (2.9%) prevalence rate of positive circulating anti-intrinsic factor antibodies. The mean age at diagnosis of pernicious anemia was 60 years old and the female-to-male ratio was approximately 1.5 to 1. In Caucasians, the prevalence of the disease rises with increasing age, peaking after age 65.(11)

Time Course of Development of Vitamin B₁₂ Deficiency

The development of clinically apparent vitamin B₁₂ deficiency in individuals with complete absence of intrinsic factor (pernicious anemia with complete atrophy of the gastric mucosa or after total gastrectomy) occurs quickly, usually in one to three years. In contrast, vitamin B₁₂ deficiency with other etiologies develops quite slowly. For example, adult vegetarians with dietary deficiency of vitamin B₁₂ may not develop clinically apparent vitamin B₁₂ deficiency for 10 to 30 years.(12)

The rapid onset of vitamin B₁₂ deficiency in individuals with complete absence of intrinsic factor results from impaired reabsorption of vitamin B₁₂, which is secreted in bile.(13),(14) Two thirds of the vitamin B₁₂ secreted into the bile is normally reabsorbed by the terminal ileum.(15) In the absence of intrinsic factor, reabsorption of biliary vitamin B₁₂ by the terminal ileum fails to occur; therefore, vitamin B₁₂ deficiency develops rapidly.(16),(17)

Pernicious Anemia: Other Findings

Patients with pernicious anemia may present with other autoimmune endocrinopathies such as chronic autoimmune thyroiditis, insulin-dependent diabetes mellitus, Addison disease, primary ovarian failure, primary hypoparathyroidism, Graves' disease, vitiligo, myasthenia gravis and the Eaton-Lambert syndrome.(18) Moreover, there is a genetic predisposition -- family members of pernicious anemia patients have a higher-than-average prevalence of pernicious anemia and other autoimmune endocrinopathies.(2)

An earlier onset age (50-60 years) of pernicious anemia has been reported among African-Americans and Hispanics, which suggests a racial difference.(19),(20),(21) In addition, African-Americans with pernicious anemia have a higher prevalence of anti-intrinsic factor antibody than whites with the condition.(22)

Gastrointestinal signs and symptoms of pernicious anemia include sore tongue, stomatits, flatulence, diarrhea, mucosal ulceration and appetite loss.(23) In addition to the clinical manifestations of vitamin B₁₂ deficiency itself, patients with pernicious anemia may have other gastric complications. For example, as a result of gastric atrophy, these patients have achlorhydria, bacterial overgrowth and intestinal metaplasia of gastric mucosa.

The intestinal metaplasia of the gastric mucosa is a risk factor for gastric adenocarcinoma. A three-fold-increased risk of gastric adenocarcinoma has been reported in pernicious anemia patients as compared to general population. Gastric carcinoid tumors are also prevalent with a 13-fold proportionate excess of carcinoid tumors among patients with pernicious anemia versus in the general population.(24)

Evaluation of Vitamin B₁₂ Deficiency

Formerly, vitamin B₁₂ deficiency was diagnosed, in part, by a B₁₂ serum level less than 180 picograms/mL. However, it is now known that serum B₁₂ levels as high as 300 picograms/mL may be compatible with a diagnosis of vitamin B₁₂ deficiency. Therefore, the most accurate cutoff serum vitamin B₁₂ value for determining deficiency has yet to be determined. Measurement of serum methylmalonic acid levels, which more accurately reflect tissue vitamin B₁₂ status, is the gold standard for the diagnosis of vitamin B₁₂ deficiency.(25),(26),(27)

Once a diagnosis of vitamin B₁₂ deficiency is made, pernicious anemia may be ruled in or out using a Schilling test.(28),(29) This test is performed by giving a 1 µg to 2 µg radioactive dose of vitamin B₁₂ orally followed immediately by a parenteral flushing dose (1000 µg) of the vitamin. A 24-hour urinary collection is made, and the amount of radioactive B₁₂ appearing in the urine is measured. This amount should be in the range of 10% to 20% of the orally administered dose.

Autoantibodies to parietal cells by an indirect immunofluorescence are present in pernicious anemia. A positive test to these antibodies is sensitive but not specific. About 90% of patients with pernicious anemia have serum autoantibodies to gastric parietal cells. However, these antibodies also have been demonstrated in about 30% of non-anemic, first-degree relatives of patients with pernicious anemia and in patients with other autoimmune endocrinopathies. Aging also increases the prevalence of parietal cell autoantibodies; in the third decade, 2.5% of general population have these antibodies, whereas 9.6% have parietal cell antibodies in the eighth decade.(30) Circulating intrinsic factor antibodies are more specific than are parietal cell antibodies and are almost diagnostic of pernicious anemia (type A gastritis). Autoantibodies to intrinsic factor are found more frequently in gastric juice than serum.

A protein-bound vitamin B₁₂ absorption test is similar to the classic Schilling test except that protein-bound vitamin B₁₂ is used instead of a pure, crystalline, vitamin B₁₂ preparation. When protein-bound vitamin B₁₂ is used as the test substance, individuals with atrophic gastritis are found unable to absorb vitamin B₁₂ in sufficient amounts. This is not corrected when the test is repeated in the presence of intrinsic factor, as it would be in pernicious anemia. Since a protein-bound Schilling test is generally available only in research settings, a low serum pepsinogen level coupled with a low serum B₁₂ level and/or high methylmalonic acid level in the absence of intrinsic factor antibodies can be used as a proxy for diagnosing a malabsorption of protein-bound vitamin B₁₂. Endoscopy is an alternative method for the diagnosis of type B atrophic gastritis and, by implication, malabsorption of protein-bound vitamin B₁₂.

In patients who have low B₁₂ levels without anemia, are otherwise asymptomatic, but are suspected to have atrophic gastritis, an alternative to the Schilling test is a therapeutic trial in which they are empirically treated with small doses of oral vitamin B₁₂ while their serum B₁₂ levels and/or serum methylmalonic acid levels are followed for normalization.

Initiating Treatment

The effects of B₁₂ deficiency are more easily reversed early in the development of deficiency, so treatment should not be withheld until any planned evaluation is complete. Actually, since a functioning intestinal mucosa is necessary to the Schilling test, and since severe B₁₂ deficiency may affect the mucosa as it does other rapid-turn-over cell populations, status should be normalized before a Schilling test is done.

The Panel on Folate, Other B Vitamins and Choline of the National Academy of Sciences has recently increased the vitamin B₁₂ recommended dietary allowance (RDA) to a value of 2.4 µg/day.(31) In atrophic gastritis, it still is not completely clear whether the RDA dose of oral vitamin B₁₂ (2.4 µg/day) is sufficient for treatment or whether, in fact, higher doses (e.g., 25-50 µg/day) should be used. The report says that 24 µg/ per day is sufficient as long as the vitamin is taken as a supplement in a fortified food (cereal product). However, because of this uncertainty at the present time, doses of either 25 µg per day (available in many multivitamin preparations) or 50 µg per day (available as a single nutrient preparation) also can be justified. The usefulness of vitamin B₁₂ in a multivitamin-mineral supplement containing iron and vitamin C has been questioned because the co-ingested vitamin C and iron could inactivate the vitamin B₁₂ molecule.(32)

If an individual patient is found to have a dietary deficiency of B₁₂, the patient should be educated with regard to foods that contain vitamin B₁₂ and be encouraged to eat these foods on a daily basis. If the patient is unwilling or unable to eat adequate quantities of B₁₂-rich foods, a one-a-day type supplement containing the RDA for vitamin B₁₂ should be prescribed.

In clinically apparent pernicious anemia, replacement of vitamin B₁₂ should be achieved through the parenteral route or as large oral daily doses. It is recommended that intramuscular injections of cyanocobalamin be given first, starting with 500 µg for 5 days, and then continuing with 1000 µg per month. In a reliable patient, an alternative chronic dosing schedule is 1 mg per day orally, since 1% of vitamin B₁₂ is absorbed by passive diffusion.(6) Recently, Kuzminski(33) reported that a daily dose of 2 mg of oral vitamin B₁₂ was as effective as 1 mg intramuscular injections in improvement of vitamin-B₁₂-deficient status (as judged by serum levels of vitamin B₁₂ and serum methylmalonic acid).

An alternative to either intramuscular or high-dose oral treatments of pernicious anemia is the administration of vitamin B₁₂ via intranasal gel. Administration of 500 µg/day to 1500 µg/day of cyanocobalamin or hydroxocobalamin has been shown to be an effective way to administer vitamin B₁₂ to deficient patients.(34),(35),(36),(37) This formulation, however, may be more expensive than other routes without offering a clear incremental benefit.

Treatment options are summarized in the Click to download this PDF documentClinician FactSheet. (Reprinted courtesy of Tufts University.)

Conclusion

Poor diet, atrophic gastritis and pernicious anemia-all common conditions among the elderly-often render a patient deficient in vitamin B₁₂. Because of the possible masking of the hematological signs of a vitamin B₁₂ deficiency by folate, a B₁₂ deficiency often manifests as paresthesias and other neurological disturbances. The insidious and potentially irreversible nature of these symptoms makes it imperative that clinicians carefully assess their elderly patients for neurological changes that may be related to vitamin B₁₂ deficiency and, when necessary, implement the appropriate therapy.

For your convenience, we are including the Click to download this PDF documentInformation for Patients handout from Nutrition in Clinical Care 2001; 4: 225. (Reprinted courtesy of Tufts University.)