Vitamin B12 deficiency is not rare, especially among older adults. It can cause anemia, memory problems, & problems with balance. We test for it when a person has anemia (especially if the red blood cells are large; see Anemia), also if they’re forgetting things or newly depressed, or if they have an unsteady gait or fall easily.
The main cause of B12 deficiency is an auto-immune disease called “Pernicious Anemia” [a terrible name]. For unknown reasons, the body forms antibodies that attack a stomach cell that produces a protein “Intrinsic Factor,” which is necessary for absorption of that vitamin. Even though B12 is present in many foods, it won’t be absorbed if the stomach is unable to make Intrinsic Factor.
Other causes of Vitamin B12 deficiency include:
- A strict vegan diet (no meat, eggs, dairy). Anyone who practices veganism should take B12 medicinal supplements.
- Stomach surgery (esp. gastric bypass)
- A stomach condition called atrophic gastritis
- Chronic excessive alcohol
- Chronic diseases of the pancreas (not diabetes)
- Long term use of certain medicines: All types of Antacids; maybe Metformin (for diabetes)
- Maybe excessive growth of bacteria in the small intestine, especially H. pylori.
Vitamin B12 deficiency can exist even if results come out in the lowish end of the “normal” range. Then we order additional tests for Methylmalonic Acid (MMA) and Homocysteine. These molecules are necessary for B12 to be used by the body, so they wind up elevated when there’s not enough vitamin around. A person can have serious neurological and mental damage from B12 deficiency without any anemia or large red blood cells. If B12 levels are within normal range, I might order these tests for someone with new memory or balance problems. We should also note that the MMA can be a little high in older adults without any B12 deficiency.
Once we diagnose Vitamin B12 deficiency, we order a test for Intrinsic Factor Antibody (IFA). If that’s positive, we know the person has Pernicious Anemia & will need Vitamin B12 as a medicine for the rest of their life. We used to always give it in monthly injections, but recent studies have shown that a daily 2,000 microgram pill (2 milligrams) works just as well. We also refer the patient to a gastroenterologist for endoscopy, since some people also have abnormal stomach linings that can predispose to cancer.
If the IFA is negative, a patient can still have the disease, but we might try pausing treatment if another of the causes above seemed possible, and easy to change. Fortunately, it’s impossible to overdose on Vitamin B12, since the body just pees out excess quantity. Also, we only test IFA after we’ve diagnosed deficiency, since there are plenty of people with a positive IFA who never have any problems.
In the old days, and even now in poorer countries without easy access to testing, it was common for doctors to prescribe vitamin B12 injections to anyone who complained of being fatigued. Many such patients felt better afterwards, since any injections can have a strong placebo effect. We never do this; nobody with normal Vitamin B12 levels needs supplementation.