Exploring the sense and nonsense of food and health

An Important Vitamin: B12

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By Sally Feltner, PhD, MS, RDN

Vitamin B12 is often overlooked as to its importance to human health. Vitamin B12 is found almost exclusively in animal products. The absorption of B12 from food requires adequate levels of stomach acid, intrinsic factor (produced in the stomach) and pancreatic secretions. Even though it is a water-soluble vitamin, the body stores and reuses it more efficiently that it does other water soluble vitamins.

Vitamin B12 is needed for the metabolism of folate and fatty acids and to maintain the insulating layer of myelin surrounding nerve fibers When myelin degenerates, neurological symptoms occur that include numbness, tingling, memory loss and disorientation. If not treated, it can eventually cause paralysis and death. On the other hand, a deficiency is rare, but can be a public health concern due to marginal B12 status due to either low intake or problems with absorption.

Pernicious anemia is the major cause of severe B12 deficiency. It is an autoimmune disease in which the cells in the stomach that produce intrinsic factor are destroyed. Therefore, B12 cannot be absorbed due to a lack of intrinsic factor. The anemia can be treated with injections, nasal gels or oral megadoses. The injections and gel bypass the GI tract and thus there is no need for intrinsic factor. Megadoses can allow adequate amounts of B12 to be absorbed that then do not require intrinsic factor.

Another cause of B12 deficiency is due to an estimated 10 to 30% of people over 50 years old are who are unable to absorb food-bound B12 normally because they have a condition known as atrophic gastritis which is an inflammation of the stomach lining that results in reduced stomach acid and bacterial overgrowth.

Vegan diets are a concern due to B12 found only in animal foods. Severe deficiencies have been found in breast – fed infants of vegan women and marginal  deficiencies for all vegans if supplemental or fortified foods are not consumed in the diet.

Vitamin B12 deficiency has been blamed for causing the fatigue of anemia found in many people and supplements or injections are given as a solution. However, there are no proven benefits of B12 supplementation in people who are not found to be B12 deficient.

Source: Smolin and Grosvenor, Nutrition: Science and Applications, Third Edition


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