Vitamin B-12 comes from the family of cobalamin chemical compounds and is found bound to protein in foods. Gastric intrinsic factor in the stomach is required to release it for absorption and utilization in the body. In well nourished, omnivorous individuals, vitamin B-12 is stored in adequate amounts in the liver, which typically accumulates a 5 to 7 year supply. The daily need is minimal -- 2.4 micrograms for adult women and men -- but it is also vital to overall health.
Function of Vitamin B-12
Vitamin B-12 functions in two co-enzyme forms, adenosyl-cobalamin and methyl-cobalamin, which play an important role in the metabolism of energy-yielding nutrients. It acts along with folic acid in the production of hemoglobin. It is also essential for normal DNA and fatty acid synthesis, helps build bones, and protects the sheath around nerve fibers. Vitamin B-12 aids in the formation of all of the bodies blood cells, and along with folic acid, is necessary for the formation of red blood cells.
Sources and Availability of Vitamin B-12
The most well-absorbed source of vitamin B-12 in the body is animal foods. Some of the richest sources include liver and kidney meat, milk, eggs, fish, cheeses, and muscle meat. For a vegetarian or vegan, it is important to obtain alternative and reliable sources to prevent deficiencies. Non-animal sources include fermented foods such as bacteria, algae, and fungi, as well as, fortified products including meat analogs, soy milk, and cereals. Foods may lose some B-12 when cooked to temperatures greater than 212 degrees F; it is also slowly destroyed in the presence of acid. As gastric acid, or intrinsic factor, is required to cleave B-12 and make it available to the body, individuals who have had major gastric surgery, such as a gastric bypass, may lack adequate intrinsic factor and may need supplementation.
Vitamin B-12 Deficiency
Deficiencies in vitamin B-12 can cause impaired cell division in rapidly dividing cells through arrested synthesis of DNA. Low levels in the blood affect growth and repair of body cells, can cause fatigue, malfunctioning of nerves and muscles, and may lead to paralysis. Symptoms take years to develop, so those at risk should be tested and supplemented appropriately. Iron and vitamin B-6 deficiency decrease absorption of B-12. Hematological symptoms, or anemia, can be masked by high folic acid intake, particularly in vegetarians.
Age-Related Deficiency
Deficiency in vitamin B-12 is common in older adults because the efficiency of absorption decreases with age. Deficient elderly individuals are often asymptomatic or they may develop psychiatric manifestations such as impaired mentation and depression. Vitamin B-12 deficiency may play a role in the development of Alzheimer's disease due to the high prevalence of deficiency later in life; investigation is ongoing.
References
- "American Dietetic Association"; Vitamin B-12; 2011
- Vitamin B-12 (cobalamin)
- "Nutrition Journal"; A Randomised Controlled Trial Investigating the Effect of Vitamin B12 Supplementation on Neurological Function in Healthy Older People; AD Dangour et.al; March 2011
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