Fundamentals of Human Nutrition/Vitamin B12< Fundamentals of Human Nutrition
8.6 Vitamin B12Edit
Vitamin B12 is a water soluble vitamin also known as Cobalamin. Water soluble vitamins are hydrophilic and are absorbed directly into the blood where they travel freely in water filled compartments though out the body. The water soluble vitamins are less likely to create toxicity in the body due to the daily excretion of excess vitamins in urine. B12 helps with the synthesis of new cells, is a coenzyme to folate, and helps to break down fatty acids and amino acids in the daily diet (Whitney, 2002).
Vitamin B12 is only found it animal products including: meat, fish, poultry, milk cheese and eggs. Since B12 is not naturally occurring in grains, it can be fortified into different cereals and breads (Whitney, 2002). The vitamin is also produced in the colon of humans by bacteria, but not enough is absorbed to be considered a good source. In ruminants B12 is synthesized using bacteria and cobalt, it is carried to the blood and enterocytes on the carrier Transcobalamin (Albert, 1980).
B12 creates the coenzyme to help activate folate, and helps to maintain nerve cells by protecting and synthesis of the myelin sheath. Another important function is the synthesis of new cells, specifically red blood cells with the production of hemoglobin and the synthesis of the coenzyme methylcobalamin. Some methylcobalamin is converted into homocysteine, which can result in cardiovascular disease at high concentrations (“Coenzyme Functions”).
The Recommended Dietary Allowance (RDA) set in 1998 for adults is 2.4 µg/day.
People over the age of 50 need higher amounts due to a decrease in absorption (Whitney, 2002).
People who follow a vegetarian or vegan diet have a higher chance of developing a deficiency (Pawlak, 2013, 110). To avoid such deficiencies having an adequate intake of animal products such as eggs and milk for vegetarians or consuming foods that are enriched with B12 for individuals who follow a vegan diet. Supplements can also be taken to decrease the likelihood of a deficiency. Megaloblastic Anemia (large cell type) is due to a deficiency in B12 or folate; a high folate level can mask the deficiency of B12 and correct the anima, but not the damage to the heme (“Vitamin B12 Deficiency And Paralysis”).
Pernicious Anemia is caused by the lack of red blood cells due to a deficiency in B12, caused primarily by a lack of intrinsic factor. Intrinsic factor is the protein secreted by the stomach to help the intestines absorb vitamin B12. A lack in intrinsic factor can be a result of old age or Atrophic Gastritis which is the inflammation of the stomach epithelium which results in loss of the stomach mucosa cells which secrete the intrinsic factor and other digestive enzymes (Zayouna).
Muscle Weakness and Paralysis- B12 deficiency can result in skeletal muscle weakness due to decreased nerve cell function, in more serious cases where the B12 stores are completely depleted paralysis can occur (Morris, 2012, p. 1457).
Memory Loss- With a deficiency fewer red blood cells are synthesized resulting in anemia, with less than usual red blood cell count a decreased amount of essential nutrients are delivered to the brain. Some people with a severe deficiency could be misdiagnosed with Alzheimer’s disease due to the similar symptoms (“Vitamin B12 Deficiency And Paralysis”).
Other deficiency symptoms include fatigue and dizziness, which are side effects of anemia
There are no known toxicities for Vitamin B12 (Whitney, 2002).
Albert, M. (1980, February 21). Vitamin B12 synthesis by human small intestinal bacteria. Retrieved November 10, 2015.
Coenzyme Functions. (n.d.). Retrieved November 10, 2015.
Morris, M. (2012). American Geriatrics Society. Vitamin B-12 and Folate Status in Relation to Decline in Scores on the Mini-Mental State Examination in the Framingham Heart Study, 60, 1457–1464-1457–1464.
Pawlak, R. (2013). How prevalent is vitamin B 12 deficiency among vegetarians? In Nutrition Reviews (Vol. 71, pp. 110-117).
Vitamin B12 Deficiency And Paralysis | Vitamin B12 Patch. (2010, August 11). Retrieved November 10, 2015.
Whitney, E., & Rolfes, S. (2002). The Water Soluble Vitamins: B Vitamins and C Vitamins. In Understanding nutrition (9th ed.). Belmont, CA: Wadsworth.
Zayouna, N. (n.d.). Atrophic Gastritis. Retrieved November 10, 2015.