Vitamin Ba dozen 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. In mammals, cobalamin is a cofactor for only two enzymes, methionine synthase and L-methylmalonyl-coenzyme A mutase (2).
Cofactor to have methionine synthase
Methylcobalamin will become necessary into purpose of the folate-founded chemical, methionine synthase. So it chemical will become necessary on synthesis of one’s amino acidic, methionine, out of homocysteine. Methionine in turn becomes necessary on the synthesis out of S-adenosylmethionine, a methyl group donor included in of a lot physiological methylation reactions, for instance the methylation regarding a great amount of internet within this DNA, RNA, and necessary protein (3). Aberrant methylation out-of DNA and protein, which causes changes in chromatin structure and you will gene phrase, is a common element out of cancers muscle. Inadequate aim of methionine synthase may cause an accumulation of homocysteine, that has been of enhanced danger of cardiovascular illnesses (Contour step one).
Cofactor having L-methylmalonyl-coenzyme A great mutase
5-Deoxyadenosylcobalamin is required by the enzyme one catalyzes the brand new sales away from L-methylmalonyl-coenzyme An inside succinyl-coenzyme An excellent (succinyl-CoA), which in turn enters brand new citric acidic years (Contour dos). Succinyl-CoA plays an important role regarding the creation of time out-of lipids and healthy protein and it is required for the forming of hemoglobin, the oxygen-carrying pigment inside red-colored blood tissue (3).
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.
Causes of nutritional B12 deficiency
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 Peoria escort reviews 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 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).