…that could be the cause of your fatigue, memory problems and more.

Most people are familiar with “iron poor blood.” But there’s another deficiency that’s less well-known—one that can cause a variety of troubling symptoms and occurs even when people do their best to eat a healthful diet. Vitamin B-12 levels that are lower than normal can be associated with muscle weakness, fatigue and/or memory problems. More severe deficiencies can cause irreversible nerve damage…or be a factor in premature death.


The initial symptoms of low B-12 (mentioned above) can be caused by many unrelated conditions, including hypothyroidism and depression. And because older adults are the ones most likely to suffer from B-12 deficiencies, their complaints might be dismissed as normal age-related problems.

What’s more: Most doctors diag­nose B-12 anemia (lack of healthy red blood cells due to a B-12 deficiency) only when levels fall below about 200 picograms per milliliter (pg/mL) of blood serum. But older people with higher levels of B-12 can still experience symptoms.


If you have any of the symptoms above—or if a routine blood test uncovers certain abnormalities (see below)—ask your doctor to test you for B-12 anemia. Who’s at risk…

  • Adults age 50 and older. The age-related drop in pepsin and other digestive fluids can impair the body’s ability to absorb B-12. The same thing can happen in those who regularly take acid-suppressing heartburn drugs, such as esomeprazole (Nexium) or omeprazole (Prilosec).
  • Strict vegetarians and vegans. With the exception of fortified foods (such as breakfast cereals) and supplements, animal products (meat, fish, dairy, eggs, etc.) are the only sources of vitamin B-12.
  • People with pernicious anemia. About 1% to 2% of older adults have pernicious anemia, a form of B-12 anemia caused by an autoimmune disorder in which the body cannot absorb adequate levels of B-12 to make enough red blood cells. Your doctor might suspect this if you have symptoms of B-12 deficiency or if a blood test shows abnormal blood cells (see below).
  • Anyone with macrocytosis, or enlarged red blood cells. This condition is one of the first signs of a B-12 deficiency. It’s often discovered during blood tests performed for a routine physical or for conditions such as peripheral neuropathy.


The first test a doctor will order if he/she suspects a B-12 deficiency is a complete blood count (CBC), which is included in many routine checkups. Among other things, the test will show your mean corpuscular volume (MCV), the average size of red blood cells. If you have a B-12 deficiency, the red cells will usually be larger than normal. You’ll also have lower-than-expected hemoglobin (an iron-rich protein that helps carry oxygen/carbon dioxide) and hematocrit (the percentage of blood consisting of red blood cells).

However: High MCV won’t prove that you have a deficiency. The same results can be caused by other conditions, such as heavy alcohol use, folate deficiency or a precursor to leukemia. But it does alert your doctor that low B-12 is a possibility. High MCV requires further testing for B-12 and/or folate deficiency. A blood smear that shows the presence of at least one six-lobed neutrophil (white blood cell) strongly indicates a B-12 and/or folate deficiency.

You’d think that the easiest way to detect a B-12 deficiency would be to simply measure B-12, also known as cobalamin, in the blood. Many doctors who check their patients’ B-12 levels like the serum cobalamin test because it’s an inexpensive starting point (about $100 and usually covered by insurance).

If your level of B-12 is solidly in the normal range (350 pg/mL or above), you probably won’t need any other tests for B-12. But it’s not the best test in some cases. Why? The results of this test can be somewhat misleading—for instance, levels are falsely low in at least 20% of cases.

Also: Many people who have this test will be told that their B-12 is “low-normal”—a gray zone between 200 pg/mL and 350 pg/mL. The word “normal” means that they won’t be diagnosed with a deficiency…and might continue to suffer from symptoms of B-12 deficiency.


If your symptoms still suggest a B-12 deficiency but the tests are not definitive, your doctor may want to take testing to another level. To do this, he will order a blocking antibody test to look for antibodies that render intrinsic fac­tor (a protein needed to promote B-12 absorption) ineffective. A positive test indicates autoimmune B-12 deficiency (per­nicious anemia). You can easily be treated for it (see below) and will require no further testing.

If the diagnosis is still uncertain, a fairly definitive test for B-12 de­ficiency is a methylmalonic acid (MMA) test. B-12 is needed for MMA to break down fatty acids. But if B-12 is inadequate, more MMA will accumulate. One study found that 98.4% of those with elevated MMA had B-12 levels under 200 pg/mL. This test is somewhat expensive (about $200) and not always cov­ered by insurance.


Although a deficiency of B-12 can cause many troubling symptoms or even serious health problems, it’s also among the easiest of conditions to prevent—and treat.

The Institute of Medicine advises adults to get 2.4 micrograms (mcg) of vitamin B-12 daily from meat and other animal foods or from fortified foods, such as breakfast cereals. A three-ounce serving of salmon has 4.8 mcg…one cup of low-fat milk has 1.2 mcg…and a serving of fortified cereal has at least 1.5 mcg.

If you’ve tested low, you’ll probably need B-12 injections. They’re usually given in a doctor’s office or they can be self-injected once a week for eight weeks, then monthly thereafter. Patients with pernicious anemia or other conditions that impair B-12 absorption will need the injections for life. Others may be able to stop the injections once normal B-12 levels are restored.

Research has shown that oral B-12 supplements can be as effective as injections. The starting dose for a supplement is 2 mg daily…and is then lowered to 1 mg daily, then weekly and, finally, monthly.

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