Vitamin B12 Deficiency Anemia: What It Is, Symptoms, and Causes

Vitamin B12 deficiency anemia occurs when a lack of vitamin B12 causes the body to produce abnormally large red blood cells that do not function properly. The term "anemia" means either a lower-than-normal number of red blood cells or an abnormally low level of hemoglobin in each of them. Let us explain the mechanism, symptoms, and what the tests show.

What vitamin B12 deficiency anemia is

This is a decrease in the number of red blood cells due to a lack of vitamin B12. In the bone marrow, instead of mature red blood cells, many large immature precursors appear — megaloblasts. Vitamin B12 is absorbed mainly in the lower part of the ileum, and this requires intrinsic factor (Castle's intrinsic factor), which is produced by the parietal cells of the stomach. Separately from anemia, B12 deficiency can cause neurological disorders: fatty acid synthesis is disrupted, demyelination and nerve cell death are possible.

Why vitamin B12 deficiency occurs

One cause is pernicious anemia: the immune system attacks healthy stomach cells, and vitamin B12 stops being absorbed from food. Other mechanisms include surgery on the stomach or small intestine, including some bariatric procedures, Crohn's disease, celiac disease, tapeworm infestation, alcohol, long-term use of medications that reduce stomach acidity, and certain medications such as metformin, as well as nitrous oxide abuse. Dietary deficiency is less common but possible with a vegan diet without supplements and fortified foods, with restrictive diets, in infants, and with poor nutrition during pregnancy. B12 and folate deficiency is more common in older adults: approximately 1 in 10 people aged 75 and older and 1 in 20 aged 65–74.

Symptoms of anemia due to B12 deficiency

Symptoms may be absent or mild. They include pronounced fatigue, lack of energy, dizziness when standing up or with exertion, shortness of breath mainly with physical exertion, pale skin, decreased appetite, irritability, diarrhea or constipation, a painful red tongue, bleeding gums, and tingling in the hands and feet. With prolonged deficiency, signs of nerve damage are added: numbness, loss of balance, problems with concentration, confusion and dementia in severe cases, psychosis, hallucinations, and optic nerve atrophy. Some of these problems occur even without anemia.

How the diagnosis is confirmed

The doctor performs an examination, including checking reflexes and sensation, and orders tests. A complete blood count, reticulocyte count, lactate dehydrogenase, bilirubin, vitamin B12, methylmalonic acid, and homocysteine levels, and antibodies to intrinsic factor and parietal cells are possible. Sometimes esophagogastroduodenoscopy is performed, and when the picture is unclear, a bone marrow biopsy. Excess folic acid can mask the hematological manifestations of B12 deficiency.

• Pronounced fatigue and lack of energy
• Tingling and numbness of the hands and feet
• Painful red tongue and bleeding gums
• Shortness of breath with exertion and pale skin
• Problems with memory, understanding, and judgment

Complications and when to see a doctor

Without treatment, prolonged deficiency leads to megaloblastic anemia and irreversible nerve degeneration. Possible complications include nervous system problems, temporary infertility, heart disease, pregnancy complications, and birth defects; in adults with severe anemia there is a risk of heart failure. Some complications resolve with treatment, but neurological ones sometimes remain permanently. You should see a doctor for any symptoms of anemia: early diagnosis reduces the risk of lasting consequences.

On its own, it is not a reason to call an ambulance; 103/112 — for signs of stroke or heart attack and other life-threatening conditions.

This material is for reference and does not replace a doctor's consultation: the numbers on a test form are interpreted by a doctor, not a journalist.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer