Megalo Means Abnormally Large; What Does That Have to Do with Anemia?

Megaloblastic anemia is a form of anemia that occurs when the body’s bone marrow produces structurally abnormal and unusually large, immature red blood cells known as megaloblasts. A deficiency in healthy, mature red blood cells can result in fatigue, pallor, lightheadedness, aches and pains, muscle weakness, and dyspnea. Other symptoms can include gastrointestinal abnormalities such as diarrhea, nausea, and loss of appetite.


The most common causes of megaloblastic anemia are a deficiency in either/both cobalamin (B12) or folate/folic acid (B9). Both these vitamins contribute to the synthesis of DNA. Deficiencies of either/both of these vitamins can result from inadequate intake, poor absorption in the intestinal tract, some medications, or improper utilization by the body. Malabsorption can be due to stomach or intestinal surgery, diseases like Crohn’s, Celiac, or tropical sprue, and even bacterial overgrowth. Folic acid (folate) deficiency is also known to be caused by alcoholism. Vegans can develop megaloblastic anemia due to lack of meat in their diets.


Medications can interfere with B9 and B12 absorption.


Medications Affecting B9 Absorption

Medications Affecting B12 Absorption


H2 Blockers

Proton Pump Inhibitors






Macrolide Antibiotics

Phenobarbital/Seizure Medications

H2 Blockers

Vitamin C


Cobalamin (B12)deficiency is identified with neurological symptoms like tingling or numbness in the hands or feet. Additional symptoms, include balance/gait problems, vision loss due to atrophy of the nerve that transmits electrical impulses from the retina to the optic nerve, and mental confusion and/or memory loss can develop over time. Mental conditions including depression, insomnia, listlessness, and panic attacks have been linked with B12 deficiencies. Folate deficiency causes fatigue, pallor, weakness, SOB, and graying hair.


While megaloblastic anemia associate with B12 deficiency can be caused by a variety of outside sources, as noted above, an autoimmune disease known as pernicious anemia, can be at fault. Patients with the autoimmune variety of B12 deficiency lack “intrinsic factor” which is a protein made in the stomach. When the body cannot manufacture this protein, it develops antibodies that attack the body’s tissues and cells. Pernicious anemia can also occur if the patient has:

  • Too many of the wrong kind of bacteria in the small intestine, which often occurs in older adults. The bacteria use up the available vitamin B12 before the small intestine can absorb it.

Megaloblastic anemia related to B12 deficiency is treated with vitamin B12. Vitamin B12 exists in four very similar chemical forms which are:

  • Methylcobalamin – naturally occurring coenzyme; most bio-available type of B12 which means it is more readily absorbed by the body.
  • Adenosylcobalamin – also naturally occurring coenzyme type of B12; it is a key component of the myelin sheath which protects nerve cells in the body and brain.
  • Hydroxocobalamin – naturally produced by bacteria in the digestive tract (as part of digestive process); highly bioavailable form used, as either an IM injection or IV drip, to treat serious deficiencies.
  • Cyanocobalamin – a synthetic form, frequently used as a food additive, that while effective, must first be converted to adenosylcobalamin and methylcobalamine by the body.

Because of the strong correlation between B9/B12 deficiencies and intestinal malabsorption, many physicians decide to treat deficiency-related anemias via injectable B9/B12 instead of oral supplementation. While most patients receive their injections at their physician’s office, some patients perform self-injections.

According to WebMD, there are more than 400 different types of anemias. Megaloblastic anemia falls under the category of anemias caused by decreased or faulty red blood cell production. Readers should now have an increased understanding of megaloblastic anemia and its relationship to vitamins B9 and B12.

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According to WebMD, there are more than 400 different types of anemias. Megaloblastic anemia falls under the category of anemias caused by decreased or faulty red blood cell production. This blog defines this type of anemia and its causes.



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