What Does Vitamin B-12 Need In Order To Be Absorbed?

Vitamin B-12, or cobalamin, is a unique nutrient. It is the only vitamin that contains a mineral --- namely, cobalt --- and it is the only B vitamin that your body stores for prolonged periods of time. According to Dr. Elson Haas, author of the book "Staying Healthy with Nutrition," vitamin B-12 was isolated in 1926, when scientists discovered that it helped to cure a sometimes fatal illness called pernicious anemia. However, not everyone who had pernicious anemia was cured by eating cobalamin-rich foods, which led to further discoveries about how vitamin B-12 is absorbed.

Coordinated Intestinal Activity

Whenever a meal containing vitamin B-12 enters your stomach, the B-12 is released from the food by digestive enzymes. Free B-12 then attaches to gastric R-proteins, which carry it into your small intestine. The R-proteins are then split away from the B-12 by pancreatic enzymes, and the B-12 joins another protein called intrinsic factor, which is produced by the same parietal cells that secrete acid in your stomach. The intrinsic factor-B-12 complex, or IF-B12, is carried to the lower end of your small intestine, where specialized receptors --- in the presence of calcium --- absorb it through the lining of your gut. Without intrinsic factor, food-borne vitamin B-12 cannot be effectively assimilated.

Pernicious Anemia

Given the complex nature of vitamin B-12 absorption, it is easy to see how the failure of any facet of its digestion and assimilation could eventually lead to deficiency. Pernicious anemia, a phrase sometimes mistakenly used to encompass all forms of B-12 deficiency, is a specific condition characterized by the autoimmune destruction of the parietal cells in your stomach, which leads to a loss of intrinsic factor.

Other Causes of Vitamin B-12 Deficiency

Although your liver can store vitamin B-12 for many months, if you fail to absorb adequate amounts of this nutrient from your diet you will gradually use up all of your stores. Pernicious anemia is the classic form of B-12 deficiency, but other causes include a strict vegetarian diet, medications such as metformin, and bowel disorders caused by stomach surgery or celiac disease. According to a January 2011 case report in "The New England Journal of Medicine," genetic abnormalities of intestinal IF-B12 receptors may also cause a vitamin B-12 deficiency.

Considerations and Recommendations

The absorption of food-based vitamin B-12 requires adequate gastric acid and intrinsic factor production, normal pancreatic function, an intact intestinal lining and normal IF-B12 receptors. Vitamin B-12 can be supplemented orally in a free, crystalline form which bypasses normal absorption mechanisms, or it can be administered via injection. Daily needs range from 0.5 mcg for infants to 2.8 mcg for lactating females. Doses of up to 1,000 mcg daily are usually well-tolerated. If you think you need additional vitamin B-12, ask your doctor about your options.