B12: Cobalamin Deficiency

Diagnosis of B12 deficiency is typically based upon measurement of serum (blood) B12 levels. About 50% of people with subclinical disease have normal serum B12 levels. A more sensitive method of screening for vitamin B12 deficiency is measurement of serum methylmalonic acid (MMA) and homocysteine levels, which are increased early in vitamin B12 deficiency.

In humans, only two enzymatic reactions are known to be dependent on vitamin B12. In the first reaction, MMA is converted to succinyl Co-A using B12 as a co-factor. Vitamin B12 deficiency, therefore, can lead to increased levels of serum MMA. In the second reaction, homocysteine is converted to methionine by using vitamin B12 and folic acid as cofactors. In this reaction, a deficiency of vitamin B12 or folic acid may lead to elevated homocysteine levels. High homocysteine levels are possibly a risk factor for heart attack.

Source: http://www.aafp.org/afp/20030301/979.html
Robert C. Oh, CPT, MC, USA, U.S. Army Health Clinic, Darmstadt, Germany
David L. Brown. MAJ, MC, USA, Madigan Army Medical Center, Fort Lewis, WA

While many individuals easily absorb B12 via the digestive tract (more on absorption in a later issue), some may need to use a sublingual supplement, which is placed under the tongue and directly absorbed into the bloodstream. The serum tests described above can help you, your physician and dietitian determine which method of supplementation is best for you.