Vitamins B-12 and B-9, the second of which is also known as folic acid, are members of the B-vitamin complex. Both vitamins affect the synthesis of DNA and the regulation of cellular metabolism. They are also related in other ways. A deficiency of vitamin B-12 can have cause a deficiency of folic acid.
Causes of Vitamin B-12 Deficiency
Vitamin B-12 deficiency has a number of potential causes. The most common is impaired absorption of the vitamin in the digestive system, either from atrophic gastritis -- a chronic inflammatory degeneration of the absorptive capacities of the small intestine -- or an autoimmune condition known as pernicious anemia that results in the destruction of stomach cells by the body's immune system. Medical conditions and surgical procedures affecting the small intestines and the pancreas, an organ that provides critical enzymes and calcium for the absorption of vitamin B-12, can also produce a deficiency. Dietary deficiencies may occur, especially in vegans; vitamin B-12 is found almost exclusively in animal foods. However, the human body also stores enough vitamin B-12 to last several years, so this is relatively rare.
Vitamin B-12 Deficiency and Age
Elderly individuals are more at risk for low levels of vitamin B-12 compared with the younger population. This is due to the high prevalence of atrophic gastritis in the older age group. Normally, stomach acid releases all of the vitamin B-12 bound to the protein in food. But atrophic gastritis decreases the production of stomach acid, and the digestive process becomes much weaker. It also creates an environment in which anaerobic bacteria can grow in the stomach and further interfere with the absorption of B-12. However, supplemental vitamin B-12 is not bound to protein and may digest and absorb more easily in some people. Fifteen percent of adults 65 years or older had laboratory evidence of a deficiency in a one study, according to the American Academy of Family Physicians.
Relationship to Folic Acid
One of the main functions of vitamins is to bind with enzymes, a type of protein that helps facilitate critical chemical reactions, to perform a specific action. The cells require the presence of vitamin B-12 and folic acid for the activity of the enzyme methionine synthase. This enzyme is responsible for the regeneration of a molecule called methionine, which in turn plays a role in the synthesis of hormones, DNA and proteins. For example, one of these proteins acts to insulate nerve cells, and a deficiency of vitamin B-12 has the effect of harming nerve cells by interrupting this process.
Folic Acid Deficiency
The diminished activity of methionine synthase that results from a deficiency of vitamin B-12 also prevents folic acid from changing into a form the human body can use. This can cause symptoms of folic acid deficiency, even when there are adequate levels of folic acid in the diet. Therefore, folic acid is unavailable to participate in the synthesis of DNA, affecting the cells of the bone marrow first. The resulting condition, known as megaloblastic anemia, produces large, immature and hemoglobin-poor red blood cells. Fatigue and a feeling of weakness are common symptoms.
References
- Food and Agriculture Organization of the United States: Chapter 4. Folate and Folic Acid
- Oregon State University Linus Pauling Institute; Vitamin B12; Jane Higdon; March 2003
- Mayo Clinic; Vitamin B12; July 2011
- American Academy of Family Physicians; Vitamin B12 Deficiency; Robert C. Oh and David L. Brown; March 2003
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