To B or not to B? The inside scoop on vitamin B12
Susan Simmons PhD, RN, ARNP-BC

December 2012 
Volume 42  Number 12
Pages 55 - 59
  PDF Version Available!

MULTIVITAMINS PROVIDE vitamin B12 or cyanocobalamin, and vitamin B9 or folic acid, in various amounts. Do we need supplementation of these vitamins, or do we get enough in our food? What's the purpose of these vitamins?To answer these questions, this article discusses the functions of vitamin B12 as well as current evidence about the need for supplementation. The role of vitamin B9 will be discussed in a future article.Vitamin B12 promotes the growth and maintenance of nerve cells and red blood cells and also plays an important role in protein synthesis. Although unused vitamin B12 is stored mainly in the liver, some is stored in the bone marrow. In general, vitamin B12 deficiency is rare because people can store several years' worth, or about 2 to 8 mg. In contrast, daily needs are only 25 to 100 mcg.1,2 Natural sources of vitamin B12 include fish, meat, eggs, and dairy products.3Those at greatest risk for vitamin B12 deficiency include older adults, strict vegetarians, and those who can't absorb the vitamin. People with diabetes mellitus and renal insufficiency may develop deficiencies. Exclusively breast-fed infants are also at risk.1,2 (For a more complete list, see Who's at risk for low vitamin B12 levels?)Patients deficient in vitamin B12 may demonstrate a classic triad of glossitis (inflamed tongue), weakness, and ascending paresthesias. Vitamin B12 deficiency can also cause muscle weakness, spasticity, hypotension, vision changes, dementia, psychoses, and mood disorders. Other signs and symptoms can include anorexia, weight loss, low-grade fever, fatigue, malaise, and gastrointestinal symptoms such as dyspepsia, diarrhea, or constipation.3Megaloblastic anemia results when a person has low levels of vitamin B12; these low levels impair DNA synthesis and cause red blood cells to become enlarged.4 Pernicious anemia (PA) occurs in the absence of intrinsic factor (IF), which is produced and released by gastric parietal cells and is needed to absorb vitamin B12 in

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