Vitamin B12 Deficiency
Vitamin B12 is the only vitamin that is not known to have toxic effects even when taken in large doses. Patients with anemia have been given 1,000 mcg monthly injections to treat vitamin B12 deficiency without any side effects. However, for healthy individuals, large doses of vitamin B12 are not recommended. Healthy adults get enough of this vitamin from a balanced diet. Healthy adults are recommended to take one multivitamin daily that contains vitamin B12. Those at risk for vitamin B12 deficiency include the elderly and vegetarians. The elderly are at risk for atrophic gastritis, and vegetarians often need supplementation because vitamin B12 is found only in foods from animal products. A strict vegetarian diet which prohibits consumption of animal products can result in vitamin B12 deficiency.
Patients with anemia cannot absorb vitamin B12 from food or oral supplements. Therefore, vitamin B12 injections are usually required to correct anemia and to prevent irreversible neurological damage. Patients who have had surgical removal of the stomach lack intrinsic factor which is produced in the stomach, so they cannot absorb vitamin B12 from food or supplements. Patients with resection of the small bowel may not be able to absorb vitamin B12 from food and supplements. Patients with a condition of food allergy to gluten that leads to atrophy of the small bowel lining may also not be able to absorb vitamin B12 from food and supplements. Also, some medications affect the absorption of vitamin B12 in the body. For example, medication used to control blood glucose levels with type II diabetes, treatment used to lower blood cholesterol levels, and also some medications used to control unexplained diarrhea have been known to inhibit the absorption of vitamin B12 from food.