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Nora Saul, MS, RD, LDN, CDE

Manager, Nutrition Services
Joslin Diabetes Center
Boston, MA

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Doctor recommends taking vitamin b12

B12 Deficiency

Ask the Expert


I was deficient in vitamin B-12 at my last doctor's visit; what can I do to get more of this vitamin in my diet?


Vitamin B12 has many important functions in the body. It is involved in DNA synthesis which replicates our genetic material, and, along with folic acid, it supports repair of our red blood, nerve and tissue cells. Without B12 you can develop anemia because your cells cannot get the oxygen they need for metabolism. You may feel weak and listless, although B12 deficiency sometimes has no symptoms.

Vitamin B12 deficiency has a number of possible causes, but rarely is diet the cause. Many foods of animal origin, such as meat, milk, eggs and cheese, contain B12. Because vegetable products do not contain B12 unless they are fortified, people who follow a vegan diet may become B12 deficient if they do not plan their meals carefully. Fortified cereals, nutritional yeast, fortified soy milks and fortified soy meat analogs can provide B12. Even those following a vegan diet may take years to deplete their supplies of B12 (if they ate meat previously) because B12 is stored in the body for up to three to five years.

Causes of B12 deficiency include:

  • Intrinsic factor deficiency (Intrinsic factor helps your body absorb B12. Intrinsic factor deficiency is called pernicious anemia.)
  • High does of antacids consumed over long periods of time
  • Stomach surgeries
  • Gastrointestinal illness such as Crohn's disease or celiac disease
  • Atrophic gastritis, an inflammation of the lining of the stomach that often leads to low stomach acid output, which is needed for B12 absorption

Once you are deficient, you may not be able to get enough B12 from food sources alone, depending on the cause of your deficiency. You may need to take a vitamin supplemented with B12 or your health care professional may give you B12 injections.

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