Dangers of Vitamin B12 Deficiency
By Karen Appold
A vitamin B12 deficiency is most often caused by digestive system difficulties, which can occur if the body is unable to absorb B12 from foods and liquids. Most frequently this is due to a lack of intrinsic factor from the stomach or insufficient acid in the stomach. Digestive diseases that can affect absorption include inflammatory bowel disease, celiac disease, autoimmune disorders such as pernicious anemia, or diseases of the pancreas. Additionally, some medications impair B12 absorption.
Other causes include undergoing certain types of bariatric surgery that remove part of the stomach; bacterial overgrowth, which competes for vitamin B12; and alcohol consumption.
Elders are at a higher risk of developing a deficiency mainly due to decreasing absorption along with dietary changes or decreased food intake. Individuals who mainly eat a vegetarian diet are also susceptible since B12 is found strictly in animal products.
Patients should strive to maintain diets that contain a sufficient level of B12. Some foods that have a good amount of B12 content are meat, dairy products, eggs, poultry, and foods fortified with B12, such as cereals and soy milk.
If a patient has a preexisting condition that may limit B12 absorption, then a combination of B12 supplements with or without monthly B12 injections can effectively manage the deficiency. “The elderly are especially at risk of developing a B12 deficiency since absorption issues and poor dietary intake are more probable,” says Mark Gottlieb, DO, a family practice physician at Paoli Hospital in Pennsylvania. In fact, approximately 3% of individuals aged 51 and older will develop a B12 deficiency, according to the Centers for Disease Control and Prevention.
Detecting B12 Deficiency
Previously, if a patient was at risk of poor B12 absorption, a Schilling test was performed. The test uses radioisotopes to measure B12 absorption. B12-dependent metabolism causes the formation of methionine from homocysteine and the formation of succinyl coenzyme A from methylmalonyl coenzyme A. Therefore, an elevated level of homocysteine and methylmalonic acid (MMA) can indicate a B12 deficiency. Urinary excretion of MMA can also indicate B12 deficiency if markedly elevated.
The Schilling test, which, according to Tangney, is laborious for the patient but a “truly great diagnostic test,” is rarely performed because of the small amounts of radioactive compound that must be measured by laboratories that often no longer have these counters.
Making a Definitive Diagnosis
Numerous patients have both a B12 and a folate deficiency. If B12 levels are in the low-normal range, MMA and homocysteine levels can be measured. If B12 deficiency is shown, a thorough review of dietary habits as well as a Schilling test can indicate either poor B12 intake or poor absorption if no other factors are present.
Certain scenarios can give a mismatch between tissue and blood levels, causing a false-positive for B12 deficiency.
B12 Deficiency and Cognitive Decline
Therefore, markers of B12 deficiency but not serum B12 levels themselves may correlate with cognition and brain volume. According to the Rush study, results showed that high levels of four of five markers for B12 deficiency were associated with lower scores on cognitive tests and smaller brain volume.
Vitamin B12 deficiency results in megaloblastic anemia and neurologic symptomatology, including disease of the spinal cord (subacute combined degeneration of the spinal cord), nerves (peripheral neuropathy), and brain (disturbance of mood and cognition). The exact serum level cutoffs necessary to diagnose deficiency are unclear, and deficiency states with clinical symptomatology have been identified at normal serum levels.2-4
The thought is that if clinicians rely on blood smears, hematocrit, or hemoglobin levels to assess anemia, the neurological sequelae may be missed and allowed to progress, Tangney says. These are subtle changes that may progress and become irreversible if no treatment is offered for correction. High-dose vitamin B12 therapy can resolve symptoms of the neurologic syndrome, including cognitive disturbances.5,6
— Karen Appold is a freelance medical writer in Royersford, Pennsylvania.
2. Solomon LR. Cobalamin-responsive disorders in the ambulatory care setting: unreliability of cobalamin, methylmalonic acid, and homocysteine testing. Blood. 2005;105(3):978-985.
3. Lindenbaum J, Healton EB, Savage DG, et al. Neuropsychiatric disorders caused by cobalamin deficiency in the absence of anemia or macrocytosis. N Engl J Med. 1988;318(26):1720-1728.
4. Saperstein DS, Wolfe GI, Gronseth GS, et al. Challenges in the identification of cobalamin-deficiency polyneuropathy. Arch Neurol. 2003;60(9):1296-1301.
6. Kuzminski AM, Del Giacco EJ, Allen RH, Stabler SP, Lindenbaum J. Effective treatment of cobalamin deficiency with oral cobalamin. Blood. 1998;92(4):1191-1198.