What Is Vitamin B12 Deficiency Anemia?

Medically Reviewed by Carol DerSarkissian, MD on December 05, 2022
3 min read

This type of anemia means that your body doesn't have enough healthy red blood cells because you're low in vitamin B12. These cells transport oxygen throughout your body. You need vitamins -- including B12 -- to make them.

When you don't have enough red blood cells, your body doesn’t get the oxygen it needs to work like it should. Anemia may make you feel tired, weak, and short of breath.

You can get vitamin B12 deficiency anemia if you don't get enough vitamin B12 in your diet from foods like milk, eggs, and meat. You're more likely to be low in this vitamin if you're older, or you eat a vegetarian diet. It can also happen if your body can't absorb enough of it from the foods you eat.

Your intestines absorb vitamin B12 from food. A protein your stomach makes called “intrinsic factor” helps your body absorb it. When you don't have enough, you have a type of vitamin B12 deficiency anemia called “pernicious anemia.”

You can get pernicious anemia if:

  • You have an autoimmune disease that makes your immune system attack the cells in your stomach that produce intrinsic factor.
  • You have surgery to remove part of your stomach, where intrinsic factor is made.

Your body also might not absorb enough vitamin B12 if:

  • You have a disease that affects how nutrients are absorbed in your intestines, such as Crohn's disease, HIV, or some infections.
  • You have certain bad bacteria in your intestines.
  • You take some medicines, such as antibiotics and anti-seizure drugs.
  • You've had surgery to remove part of your intestines.
  • You've been infected with a tapeworm.

Anemia can make you feel tired and short of breath. Here are some other signs:

  • Your skin looks pale or yellow.
  • You feel dizzy.
  • You have no appetite.
  • You've lost weight without trying.
  • Your hands and feet feel like they're numb or tingling.
  • Your heart beats too fast or you have chest pain.
  • Your muscles feel weak.
  • You often have mood changes.
  • You're confused or forgetful.

Because these can also be symptoms of other conditions, see your doctor for a diagnosis. Your doctor will do a physical exam and might order one or more of these tests:

  • Complete blood count. This test checks the size and number of your red blood cells. If you're low in vitamin B12, your red blood cells won't look normal. They'll be much bigger and shaped differently than healthy ones.
  • Vitamin B12 level. This test checks to see if you have enough of it in your blood.
  • Intrinsic factor antibodies. These proteins tell your immune system to attack intrinsic factor. If you have pernicious anemia, you'll have them in your blood.
  • Schilling test. This test uses a radioactive form of B12 to see if your body has enough intrinsic factor.
  • Methylmalonic acid level (MMA). This test measures the amount of MMA in your blood. When your vitamin B12 level is low, your level of MMA rises.

Usually, vitamin B12 deficiency anemia is easy to treat with diet and vitamin supplements. To increase the amount of vitamin B12 in your diet, eat more of foods that contain it, such as:

  • Beef, liver, and chicken
  • Fish and shellfish such as trout, salmon, tuna fish, and clams
  • Fortified breakfast cereal
  • Low-fat milk, yogurt, and cheese
  • Eggs

Your doctor might recommend that you also take a vitamin B12 supplement. It comes in pills or a nasal spray. If you are very low in this vitamin, you can get higher-dose vitamin B12 shots. You may need to take vitamin B12 for the rest of your life. You might also need to get treated for the condition that causes your anemia.

But increasing your vitamin B12 levels is a key thing you can do. If you let it go for too long, it can damage your heart, brain, nerves, bones, and other organs in your body. With treatment, you should feel better and avoid any long-term problems.