What causes vitamin B12 deficiency?

Jill A. Grimes, MD
Family Medicine
B12 deficiency has several possible causes. Some people get it as a side effect from bariatric surgery (a stomach bypass), but most get B12 deficiency from making antibodies to B12 receptors in your stomach. When this happens, you can no longer absorb B12 from your diet, so the only ways to get B12 is from a shot or from a medicine that can be absorbed under your tongue, or more recently, a medicine you squirt in your nose (in the same manner as allergy nose sprays). When you bypass the stomach receptors, the B12 can then enter your body effectively.

Who is prone to getting B12 deficiency? Anyone with other autoimmune diseases, where the body starts making antibodies to other organs or receptors. This includes adult onset diabetes, vitiligo, thyroid disease, and other diseases in the rheumatic family such as lupus.
Elizabeth Casparro, MPH,RD
Nutrition & Dietetics

Vitamin B12 deficiency can be caused by 2 main reasons: lack of intake or lack of absorption. Lack of intake most often occurs with vegans because vitamin B12 is naturally only found in animal products. This can be compensated for by taking a supplement or finding foods that are fortified with vitamin B12 (some vegans do allow brewer's yeast). Lack of absorption is usually due to low stomach acidity because a molecule called intrinsic factor, which aids in vitamin B12 absorption, is only released by the stomach at a certain pH. Low stomach acidity occurs as one ages and with the use of antacids and proton pump inhibitors (i.e. Prevacid, Protonix, Zantac, etc.). If this is the case, then B12 can be given as a shot.

Inadequate intake rarely causes vitamin B12 deficiency because this vitamin is plentiful in eggs, dairy products, meat, fish, and poultry, and it's efficiently stored in the liver. Instead, deficiency usually occurs because an individual can't absorb the vitamin from food. Untreated B12 deficiency can have a variety of consequences, including pernicious anemia, a condition in which your body is unable to produce enough red blood cells.
There are several ways people can develop a vitamin B12 deficiency. Many people simply don't eat enough foods rich in vitamin B12, including meat, poultry, shellfish, eggs and dairy products. Some people may consume a diet rich in vitamin B12 but aren't able to benefit from it because genetics, disease or surgery caused them to have stomach linings with too little intrinsic factor, a substance that's needed to absorb vitamin B12 from food.

People over age 50 are less able than younger people to absorb B12 from food, which may lead to deficiency. Other factors that can lead to malabsorption and vitamin B12 deficiency include alcoholism, overuse of heartburn medications and certain conditions such as Crohn's disease or celiac disease. Talk to your doctor if you think you might be deficient in vitamin B12.
Some possible causes of low B12 include the following:
  • Diet low in B12 -- usually lacking meat, fish, eggs or dairy products
  • Previous abdominal or intestinal surgery that affects absorption
  • Crohn's disease
  • Tapeworm infection
  • Malabsorption disorders
  • Pernicious anemia

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.