Vitamin B12 – What you need to know? (part 1)

The vitamin B12 is seldom found in foods derived from plants; therefore, animals and humans that consume strict vegetarian diets are very likely to have sub optimal intakes of vitamin B12 which, if prolonged and uncorrected, will lead to anemia and, ultimately, to peripheral neuropathy.

B12 deficiency is extremely common in India as is Vitamin D, folic acid, or iron deficiency, because malnutrition is extremely common, even among the rich. It can coexist with other nutritional deficiencies or medical disorders. Low vitamin B12 status can also occur in individuals with deficiencies in proteins involved in vitamin B12 transport and/or metabolism, and in individuals with compromised gastric parietal cell function. Low vitamin B12 status impairs the metabolic utilization of folate and contributes to homocysteinemia, a risk factor for occlusive vascular disease

 History of B12 (Cobalamin)

1855Thomas Addison coined the name “pernicious anemia”, not responding to iron therapy, neuropsychiatric problems, succumbed to illness within 1 to 3 yearsof diagnosis
1908Whipple reported success of a liver diet inexperimental dogs subjected to repeatedphlebotomies.
1926George Richards Minot and William P. Murphysubjected 45 patients with pernicious anemiato a liver therapy, that included nearly raw liverwith mutton/beef and fresh fruits, significantimprovement as observed
1934Minot, Murphy, and Whipple shared the Nobel Prize
1935William B. Castle described the intrinsic factor (IF).He noticed that all patients with pernicious anemiawere not improving with the liver therapy; somedid not respond at all. He hypothesized that there was an extrinsic factorin the liver diet (which we now know as B12), but itneeded an IF from the stomach to complete its action.To prove his hypothesis Castle consumed mutton andafter that he aspirated his own gastric secretion.He then transferred this gastric aspirate into thosepernicious anemia patients who did not improveafter consuming the liver diet.
1948In Dorothy Crowfoot Hodgkin determined thechemical structure of the molecule

Transportation and Absorption of Vitamin B12

Absorption of B12 is both passive and active; Passive absorption is possible through buccal, duodenal and ileal mucosa but it is very inefficient with only less than 1% of an oral dose absorbed. With 1000 mcg oral or S/L dose – <10% may get absorbed. Active absorption is from the ileum; it is an efficient mechanism and is mediated by IF secreted from the gastric parietal cells

Characteristics of Vitamin B12

   Vitamin B12 exists in several forms and contains the mineral cobalt, compounds with vitamin B12 activity are called “cobalamins”. Methylcobalamin and 5-deoxyadenosylcobalamin are the forms of vitamin B12 that are active in human metabolism.  The other Important Dietary Forms are Cyano-, aqua-, hydroxo-, methyl-, and 5’-deoxyadenosylcobalamins

  The corrinoids are red, red–orange or yellow crystalline substances. They are solublein water, and are fairly stable to heat but decompose at temperatures above 210°C without melting.

Functions of Vitamin B12

  • Vitamin B12 functions in metabolism in two coenzyme forms: adenosylcobalamin and methylcobalamin
  • Methionine synthetase catalyzes the methylation of Hcy to regenerate methionine, serving as the methyl group carrier (via methylcobalamin)
  • The adenosylcobalamin-dependent enzyme methylmalonyl- CoA mutase catalyzes the conversion of MMA- CoA to succinyl-CoA in the degradation of propionate formed from odd-chain fatty acids
  • PK. (2017). B12 deficiency in India. Archives of Medicine and Health Scineces(5), 261 – 268.

Groff J, Gropper S. Advanced Nutrition and Human Metabolism, 3rd ed. Wadsworth: 2000

Combs G. Vitamin B12 in The Vitamins. New York: Academic Press, Inc., 1992

Gerald FC Jr, The Vitamins: Fundamentals Aspects in Nutrition and Health. Considering the individual vitamins: Vitamin B12, 377-394. 4th Ed, Elsevier Inc, 2012.

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