Anemia - Introduction

Other medications that increase the risk for anemia are certain antibiotics, some antiseizure medications (e.g., phenytoin), immunosuppressive drugs (e.g., methotrexate, azathioprine), antiarrhythmic drugs (procainamide, quinidine), and anti-clotting drugs (aspirin, warfarin, heparin).

Megaloblastic Anemia

Megaloblastic anemia is the end product of deficiencies in the B vitamins folate, vitamin B12 (also called cobalamin), or both. Such deficiencies produce abnormally large red blood cells (megaloblastic) that have a shortened life span. Neurologic problems are also associated with these deficiencies. There are a number of conditions that can cause these deficiencies.

Click the icon to see an image of red blood cells seen in megaloblastic anemia.

Causes of Vitamin B12 Deficiency. Conditions that cause vitamin B12 deficiencies include the following:

Pernicious anemia. Pernicious anemia is an autoimmune disease in which antibodies are tricked into attacking stomach cells. This results in impaired production of intrinsic factor (IF), a compound that is critical for absorption of vitamin B12. Pernicious anemia is diagnosed in about 1% of people over 60, with women having a higher risk than men.
H. pylori and atrophic gastritis. A 2000 study suggested that the H. pylori bacterium is a player in many cases of vitamin B12 deficiency. The bacteria are not only major culprits in peptic ulcers, but also are strongly associated with atrophic gastritis. This condition is a gradual loss of the stomach lining and is a known cause of vitamin B12 deficiency. (Some researchers theorize that H. pylori-induced injuries in the stomach lining may actually be the first step in the destructive process that leads to pernicious anemia.)

Click the icon to see an image of a peptic ulcer.

Complications of gastrointestinal surgery. Surgeries such as stomach bypass or stapling, which remove part or all of the stomach, pose a 15 - 30% chance of causing vitamin B12 deficiencies.
Overgrowth of intestinal bacteria.
Tropical sprue (an acquired malabsorption disease occurring in tropical climates).
Overexposure to nitrous oxide.

Vitamin B12 deficiency from diet is very rare, since the liver stores over a three-year supply. It usually does not occur even in alcoholism, vegetarianism, or in malnourished people with kidney failure or cancer. Since animal products are the chief source, however, true vegan vegetarians may need a supplement, fortified food, or appropriate food selection known to contain adequate amounts of this vitamin.