Vitamin B12 deficiency anemia: dietary cobalamin deficiency

Vitamin B12 deficiency anemia is a type of anemia caused by a lack of this essential vitamin.

Anemia is a condition characterized by a reduced number of healthy or normal red blood cells, a decreased concentration of hemoglobin in the blood, or a hematocrit level (average values range from 41–53% in men and 36–46% in women) lower than normal.

Red blood cells are the most abundant cells in the blood, responsible for capturing oxygen and transporting it to various tissues throughout the body. This function is facilitated by hemoglobin, their main protein, which binds oxygen to iron atoms for transport through the bloodstream. Consequently, anemia hinders oxygen distribution to all the body’s cells, as the reduction in red blood cells results in this dysfunction.

Vitamin B12 is a bacterially-derived vitamin that plays a crucial role in the normal functioning of the brain, nervous system, blood formation, and protein synthesis. Specifically, vitamin B12 is involved in the metabolism of human cells. Its complex physiology makes it susceptible to factors that can lead to deficiency. Vitamin B12 must be released from its protein-bound form through the action of digestive peptidases in the stomach and small intestine. Gastric acid liberates the vitamin from food particles; thus, antacids and acid-blocking medications can inhibit vitamin B12 absorption. The risk of vitamin B12 deficiency increases with age, as some individuals produce less stomach acid as they grow older.

Vitamin B12 is also essential for the formation and growth of red blood cells. Therefore, one of the primary consequences of its deficiency is anemia. In vitamin B12 deficiency anemia, red blood cells are abnormally large, referred to as macrocytes, and as megaloblasts when observed in the bone marrow. This is why this anemia is also classified as a form of megaloblastic anemia.

Symptoms are typically mild but may include:

• Diarrhea or constipation
• Fatigue, lack of energy, or dizziness when standing or exerting oneself
• Loss of appetite
• Pale skin
• Irritability
• Difficulty concentrating
• Shortness of breath, especially during exercise
• Swelling and redness of the tongue or bleeding gums

Primary causes for this type of anemia include:

• Pernicious anemia: a condition in which the body destroys stomach cells that produce intrinsic factor, leading to vitamin B12 deficiency anemia
• Surgery to remove parts of the stomach or small intestine, such as weight-loss surgeries
• Intestinal disorders: conditions like Crohn’s disease, celiac disease, fish tapeworm infection, or other problems that impair digestion
• Chronic alcohol consumption
• Long-term use of antacids and medications for acid reflux
• Abuse of "laughing gas" (nitrous oxide)
• Long-term use of metformin

The main risk factors for vitamin B12 deficiency are also the main risk factors for vitamin B12 deficiency anemia. These risk factors are:

• Advanced age
• Resection of the stomach or small intestine
• Small intestinal inflammatory disease
• Autoimmune disorders, such as Graves’ disease or vitiligo

Diagnosis of vitamin B12 deficiency anemia typically involves the following laboratory tests:

• Hemogram
• Reticulocyte count
• Lactate dehydrogenase (LDH) level
• Serum bilirubin level
• Vitamin B12 level
• Methylmalonic acid (MMA) level
• Serum homocysteine level
• Anti-intrinsic factor antibodies
• Anti-parietal cell antibodies

In some cases, additional procedures may be required, such as:

• Endoscopy to examine the stomach and small intestine
• Bone marrow biopsy if the diagnosis is unclear

Treatment of vitamin B12 deficiency anemia depends on the cause of the deficiency. A balanced diet that includes vitamin B12-rich foods is also recommended.

For individuals with medical conditions that cause vitamin B12 deficiency, treatment often involves monthly injections of vitamin B12.

The best way to prevent vitamin B12 deficiency anemia is through a well-balanced diet that includes foods rich in vitamin B12.