Vitamin B12, also known as cobalamin, is a water-soluble B vitamin found in several common foods. B12 is required for DNA synthesis, and its deficiency can cause anemia and neurological dysfunction. One symptom of B12-deficiency anemia is fatigue, which can be alleviated by taking B12 supplements. However, taking B12 supplements in the absence of B12 deficiency has no effect on alleviating fatigue. If you suspect you are B12-deficient, you can see your doctor and get tested.
Sources of B12
Vitamin B12 is typically found in meat and dairy products, as well as in supplemented breakfast cereals and vegetarian imitation-meat products. It is a water-soluble vitamin, but unlike other water-soluble vitamins, which if consumed in excess are excreted in your urine, excess vitamin B12 is stored in your liver. Recommended daily intake of B12 increases with age and in pregnant or lactating women, but is generally between 2.4 to 2.8 micrograms per day.
B12 Deficiency
Vitamin B12 interacts with tetrahydrofolate to synthesize deoxythymidine triphosphate, which is one of four DNA nucleotides. Therefore, B12 deficiency impedes DNA synthesis. This causes impaired red blood cell (RBC) regeneration since these cells normally synthesize DNA at high rates. Impaired RBC production causes anemia, characterized by fatigue, weakness and constipation. More severe B12 deficiency causes neurological dysfunction, characterized by tingling in the hands and feet, forgetfulness and depression. However, because B12 is stored by your liver, deficiency may take years or decades to develop.
Causes of B12 Deficiency
B12 deficiency is typically the result of poor intestinal absorption or inadeqaute intake. Poor absorption can result from medical conditions affecting the function of your stomach and small intestine, including atrophic gastritis, pernicious anemia (an autoimmune disorder), celiac and Chron's disease. Surgery affecting your small intestine may also impair its ability to absorb B12. Inadequte intake can occur in vegetarians and vegans who do not eat foods enriched in B12 or take B12 supplements.
Fatigue
Fatigue can be caused by many things, including poor sleep, heart and lung disease, endocrine disorders, cancer and infection. Although B12 deficiency can cause anemia-related fatigue, there is no good evidence that taking B12 supplements for fatigue in the absence of B12 deficiency has any benefit. However, if you are B12-deficient, taking B12 supplements may cure your fatigue. The only way to determine whether or not you are B12 deficient is to see a doctor and get tested.
Testing
If you suspect you are B12-deficient, you can see your doctor and get tested. B12 tests first determine whether there is a B12 deficiency, and then determine the cause of that deficiency. Typically, treatment involves taking B12 supplements. If you undergo B12 tests and are found not to have a B12 deficiency, but you are still feeling fatigued, your doctor may choose to test for some of the other causes of fatigue listed above.
