Vitamin B_several has the largest and most complex chemical structure of all the vitamins. For this reason cobalamin is the term used to refer to compounds having vitamin B₁₂ activity. Methylcobalamin and 5-deoxyadenosylcobalamin are the forms of vitamin B₁₂ used in the human body (1). The form of cobalamin used in most nutritional supplements and fortified foods, cyanocobalamin, is readily converted to 5-deoxyadenosylcobalamin and methylcobalamin in the body Alexandria escort reviews. In mammals, cobalamin is a cofactor for only two enzymes, methionine synthase and L-methylmalonyl-coenzyme A mutase (2).

Cofactor to own methionine synthase

Methylcobalamin will become necessary with the function of the new folate-oriented chemical, methionine synthase. It enzyme is necessary towards the synthesis of your own amino acidic, methionine, out-of homocysteine. Methionine consequently is necessary toward synthesis out of S-adenosylmethionine, an effective methyl class donor utilized in of several physiological methylation responses, such as the methylation from many web sites within this DNA, RNA, and you may healthy protein (3). Aberrant methylation out of DNA and you may healthy protein, that causes changes in chromatin design and you may gene phrase, is actually a common ability out-of cancer muscle. Useless reason for methionine synthase may cause a collection of homocysteine, that has been of this enhanced risk of cardiovascular disease (Profile step 1).

Cofactor getting L-methylmalonyl-coenzyme Good mutase

5-Deoxyadenosylcobalamin becomes necessary of the enzyme you to catalyzes the new conversion process of L-methylmalonyl-coenzyme An inside succinyl-coenzyme A good (succinyl-CoA), which then gets in brand new citric acid stage (Figure dos). Succinyl-CoA takes on an important role regarding the production of energy regarding lipids and necessary protein and is necessary for the formation of hemoglobin, the new clean air-carrying pigment for the yellow bloodstream tissue (3).

Deficit

In healthy adults, vitamin B₁₂ deficiency is uncommon, mainly because total body stores can exceed 2,500 ?g, daily turnover is slow, and dietary intake of only 2.4 ?g/day is sufficient to maintain adequate vitamin B₁₂ status (see RDA) (4). In elderly individuals, vitamin B₁₂ deficiency is more common mainly because of impaired intestinal absorption that can result in in B₁₂ deficiency in this population.

Reasons for vitamin B12 lack

Intestinal malabsorption, rather than inadequate dietary intake, can explain most cases of vitamin B₁₂ deficiency (5). Absorption of vitamin B₁₂ from food requires normal function of the stomach, pancreas, and small intestine. Stomach acid and enzymes free vitamin B₁₂ from food, allowing it to bind to R-protein (also known as transcobalamin-1 or haptocorrin), found in saliva and gastric fluids. In the alkaline environment of the small intestine, R-proteins are degraded by pancreatic enzymes, freeing vitamin B₁₂ to bind to intrinsic factor (IF), a protein secreted by specialized cells in the stomach. Receptors on the surface of the ileum (final part of the small intestine) take up the IF-B₁₂ complex only in the presence of calcium, which is supplied by the pancreas (5). Vitamin B₁₂ can also be absorbed by passive diffusion, but this process is very inefficient-only about 1% absorption of the vitamin B₁₂ dose is absorbed passively (2). The prevalent causes of vitamin B₁₂ deficiency are (1) an autoimmune condition known as pernicious anemia, and (2) a disorder called food-bound vitamin B₁₂ malabsorption. Both conditions have been associated with a chronic inflammatory disease of the stomach known as atrophic gastritis.

Atrophic gastritis

Atrophic gastritis is thought to affect 10%-30% of people over 60 years of age (6). The condition is frequently associated with the presence of autoantibodies directed toward stomach cells (see Pernicious anemia) and/or infection by the bacteria, Helicobacter pylori (H. pylori) (7). H. pylori infection induces chronic inflammation of the stomach, which may progress to peptic ulcer disease, atrophic gastritis, and/or gastric cancer in some individuals. Diminished gastric function in individuals with atrophic gastritis can result in bacterial overgrowth in the small intestine and cause food-bound vitamin B₁₂ malabsorption. Vitamin B₁₂ levels in serum, plasma, and gastric fluids are significantly decreased in individuals with H. pylori infection, and eradication of the bacteria has been shown to significantly improve vitamin B₁₂ serum concentrations (8).