Vitamin B12 Deficiency Anemia: Symptoms and Risks

Medically Reviewed by Shruthi N, MD on June 26, 2024
Written by Kathryn Whitbourne
8 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 iron and vitamins -- including B12 -- to make red blood cells.

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 have vitamin B12 deficiency anemia if you don't get enough vitamin B12 in your diet from foods like milk, eggs, and meat, or if your body can't absorb B12 because of a health problem. Your intestines absorb B12 from food. Here some of the most common reasons for vitamin B12 deficiency: 

Pernicious Anemia

This is the most common cause of vitamin B12 deficiency worldwide and mainly affects people of Northern European ancestry. "Pernicious" means "harmful" or "destructive." This type of B12 deficiency anemia can affect many body systems and cause problems in your gut, heart, and muscles.  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, a protein that helps your body absorb B12.
  • You have atrophic gastritis, an inflammation of the stomach lining. This decreases production of intrinsic factor and secretion of hydrochloric acid in the stomach, two things that affect your body's absorption of B12. (Hydrochloric acid separates B12 from the protein it's attached to in food; the freed B12 combines with intrinsic factor so that the body can absorb the vitamin). 
  • You have a family history of the illness (rare).

Restricted diets

Vitamin B12 is only found in animal products like meat, eggs, and milk. So if you're on a vegan or vegetarian diet where you're not eating foods from animals, you're at risk for B12 deficiency. 

Certain health conditions

If you have a stomach or small intestine condition such as celiac disease or Crohn's disease, you may not be able to absorb enough vitamin B12 from food.

Health conditions like HIV, diabetes, and alcohol use disorder (alcoholism) put you at risk for vitamin B12 deficiency. A rare cause is transcobalamin II deficiency, a genetic condition where your body can't transport B12 (also known as cobalamin) in your body. 

Certain medications

The following drugs can reduce levels of vitamin B12 in your body:

  • Antibiotics -- long-term use can lower vitamin B levels generally
  • Anti-seizure drugs
  • Chemotherapy medicines, especially methotrexate
  • Drugs used to reduce stomach acid, like H2 blockers (Pepcid AC, Tagamet, Zantac) and proton pump inhibitors (Nexium, Prevacid, Prilosec)
  • Metformin (Glucophage) -- taken for diabetes
  • Colchicine -- taken for gout
  • Some cholesterol-lowering medications 

Other causes

  • You're over 65. Older adults are more likely to have vitamin B12 deficiency because they're prone to not having enough hydrochloric acid in their stomachs. This means they can't absorb B12 from food, though they can from a supplement. And they're at higher risk for atrophic gastritis. Around 8-9% of people over 65 have atrophic gastritis compared to 2% of the general population.
  • You've had bypass surgery for weight loss, which removes part of your stomach. This also causes a loss of cells that produce intrinsic factor and secrete hydrochloric acid.
  • You have certain bad bacteria in your intestines.
  • You've been infected with a tapeworm. Tapeworms eat vitamin B12.
  • You abuse nitrous oxide (laughing gas). Nitrous oxide prevents your body from absorbing B12.

Your body stores 1,000 to 2,000 times as much vitamin B12 as you eat in a day. So it can take 2-5 years before you see signs of B12 deficiency. Some people with the condition don't have any symptoms, at least at first. Here are the most common signs of B12 deficiency: 

Physical symptoms

  • You feel tired and lack energy.
  • Your skin looks pale or yellow.
  • You have nausea, vomiting, or diarrhea.
  • You feel dizzy.
  • You have no appetite.
  • You've lost weight without trying.
  • Your heart beats too fast or you have chest pain.
  • Your muscles feel weak.

Neurological symptoms (symptoms of problems in brain, spinal cord, or other nerves)

  • Your hands and feet feel like they're numb or tingling.
  • You have vision problems.
  • You feel confused or forgetful.
  • You have difficulty walking or speaking as you used to.
  • Neurological problems from B12 deficiency may be permanent.

Psychological symptoms

  • You often have mood changes.
  • You feel depressed.
  • You feel irritable.

Differences in symptoms of pernicious anemia vs. vitamin B12 deficiency anemia

The main difference in the two conditions is pernicious anemia is due to your body not being able to absorb B12, while other types of B12 anemia may be due to your not having enough of the vitamin in your diet. But the symptoms are the same for both.

It can take up to 5 years before you start to see symptoms of pernicious anemia. Often you'll have the neurological or psychological symptoms before the anemia (low red blood cell count) is present. This means there's a big chance of being misdiagnosed because many other conditions have these symptoms too. 

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. 

Hemoglobin is a protein in your red blood cells. Your hemoglobin level should be 13 g/dL (grams per deciliter) or higher for men or 12 g/dL or higher for women. If your level is 12 g/dL or lower for men and 11 g/dL or lower for women, you have anemia.

Vitamin B12 level. This test checks to see if you have enough of it in your blood. If your B12 level is below 200 pg/mL (picograms per milliliter), you're considered to have a deficiency. A normal level is 400 pg/mL or higher.

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.

Your doctor should also take a thorough medical history, asking you about symptoms and whether you had diseases like celiac disease or Crohn's disease; what your diet is like; and which surgeries you've had. Because B12 symptoms can look like symptoms of other diseases, diagnosing a B12 deficiency can be challenging.

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, 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're very low in B12, you can get higher-dose vitamin B12 shots. You may need to take vitamin B12 for the rest of your life, especially if you have neurological symptoms. You might also need to get treated for the condition that causes your anemia. For instance, you may need antibiotics if your anemia was caused by bad bacteria.

Rarely, you may get a blood transfusion along with B12 treatment. But this would be only if you were at risk of some kind of serious heart problem or other emergency situation, rather than just having low hemoglobin levels. 

 

Increasing your vitamin B12 levels is key. If you let it go for too long, it can cause problems in your nervous system such as:

  • Vision problems
  • Memory loss
  • A pricking or numbing sensation
  • Difficulty speaking or walking due to ataxia (loss of physical coordination)
  • Damage to your extremities (hands, feet, arms, etc.), particularly your legs

Other problems could include

  • Infertility (this should go away with B12 treatment)
  • Stomach cancer
  • Bleeding and infections
  • Damage your heart, brain, bones, and other organs in your body

If you're pregnant and don't get enough vitamin B12, your baby is at risk of a serious birth defect called a neural tube defect. The neural tube is a narrow channel that eventually forms the brain and spinal chord. If it's defective, your baby might end up with a spine or brain that doesn't develop properly.  

It's best to get treated for B12 deficiency anemia and avoid any long-term problems.

You can prevent B12 deficiency by:

  • Eating animal products, like meat, fish, eggs, and milk.
  • Looking for foods fortified with vitamin B12. These could be breakfast cereals and breads, nutritional yeast, or milk made from plants. Check the labels to make sure B12 is included. 
  • Taking vitamin B12 supplements. B12 might be part of a multivitamin or a standalone supplement. Check the labels.
  • Cutting down or eliminating alcohol. Too much alcohol can damage your digestive system, which makes it hard for your body to absorb B12.
  • Not misusing nitrous oxide.

It can take years to see the effects of vitamin B12 deficiency anemia. The most common symptom is feeling tired and weak. You may be misdiagnosed because the symptoms (tiredness, dizziness, tingling in hands and feet) can be symptoms of other illnesses too. Treatment and prevention involve eating meat, fish, and dairy products or foods fortified with B12, like some breakfast cereals and breads. You can also take a vitamin B12 supplement. In more serious cases, you might need an injection of B12.

Why are vegetarians more prone to vitamin B12 deficiency?

B12 only comes from animal products. If you're a vegetarian who eats dairy, you can probably get enough B12 from eggs, milk, and other dairy products. If you're a strict vegetarian or vegan, you're at higher risk of B12 deficiency since plant-based foods don't naturally have B12. But you can get it from fortified plant milks, breakfast cereals, and other foods (check the labels to make sure B12 is included). Or you might need to take a B12 supplement.