Vitamin B12

Vitamin B12 (cobalamin), a member of the corrin family, is a cofactor for the conversion of methylmalonyl Coenzyme-A (CoA) to succinnyl CoA. In addition, vitamin B12 is a cofactor in the synthesis of methionine from homocysteine, is implicated in the formation of myelin, and, together with folate, is required for DNA synthesis. Impaired vitamin B12 status, which may lead to clinical deficiency, is common in mixed patient populations, especially in those older than 60 years. Vitamin B12 deficiency can occur in patients with autoimmune disease (pernicious anaemia), severe primary hypothyroidism, those with ileal disease, patients on chronic therapy with antacids, proton pump inhibitor or H2 antagonists, or colchicine, and in chronic malnutrition states including alcoholism. Common causes also include adherence to vegetarian and vegan diets. A serum B12 test measures all cobalamins – holoTC (20-30%) and B12-haptocorrins (70-80%). Values below the normal expected range (except for pregnancy and congenital haptocorrin deficiency) may indicate that tissue B12 stores are becoming depleted. However, a B12 level in the low-normal range does not ensure that vitamin B12 levels are sufficient and patients may require further evaluation with other tests e.g. Active B12 (holoTC), homocysteine and methylmalonic acid.