Vitamin B12

INTRODUCTION

Vitamin B12 is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement and a prescription medication. Vitamin B12 exists in several forms and contains the mineral cobalt [1-4], so compounds with vitamin B12 activity are collectively called “cobalamins”. Methylcobalamin and 5-deoxyadenosylcobalamin are the forms of vitamin B12 that are active in human metabolism..

Vitamin B12 is required for proper red blood cell formation, neurological function, and DNA synthesis . Vitamin B12 functions as a cofactor for methionine synthase and L-methylmalonyl-CoA mutase. Methionine synthase catalyzes the conversion of homocysteine to methionine .Methionine is required for the formation of S-adenosylmethionine, a universal methyl donor for almost 100 different substrates, including DNA, RNA, hormones, proteins, and lipids. L-methylmalonyl-CoA mutase converts L-methylmalonyl-CoA to succinyl-CoA in the degradation of propionate .an essential biochemical reaction in fat and protein metabolism. Succinyl-CoA is also required for hemoglobin synthesis.

CHEMICAL NAME

cyanocobalamin

 

STRUCTURE

DIETARY SOURCES

1. Animal Liver and Kidneys

2. Clams

3. Sardines

4. Beef

5. Fortified Cereal

6. Tuna

7. Fortified Nutritional Yeast

8. Trout

9. Salmon

10. Fortified Nondairy Milk

RECOMMENDED INTAKES

Intake recommendations for vitamin B12 and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine (IOM) of the National Academies (formerly National Academy of Sciences

PHYSIOLOGICAL ROLE

Vitamin B12 has a protective role against cancer, especially those which are due to smoking. Given that smokers have a very low level of vitamins B12 and folic acid, the researchers decided to investigate what is the effect of adding these vitamins to smokers. They found that smoking reduces the levels of these vitamins primarily in the cells of the lungs and the combinations of these two vitamins reduces the possibility of getting lung or bronchi cancer.

Vitamin B12 plays a role in protecting the body from various toxins and allergens. About this role of vitamin B12 there are not a lot of data, but it is found that it could successfully block many adverse reactions to sulfites, and other various food additives.

Vitamin B12 participates in many biochemical processes, but the complete mechanism of action is not clear. Reaction capable part of coenzyme (organic molecules that are required for enzyme activity) is cobalt.

The function of vitamin B12 is closely related to folic acid. It takes part in the building up of creatine, epinephrine, nitrogen bases of nucleic acids, proteins and other biologically active substances.

Using the protein ingredient of gastric juice, vitamin B12 is absorbed from the small intestine (the ileum) in the blood. From the blood vitamin B12 is distributed into tissues, where it binds to vitamins and other nitrogen compounds by building various complexes.

Action of mechanism

Vitamin B12 or cyanocobalamin obtained from food is initially bound by haptocorrin, a protein found in the saliva with high affinity for B12. This forms a haptocorrin-B12 complex. Cyanocobalamin passes through the stomach and is protected from acid degradation due to its binding to haptocorrin. In the duodenum, pancreatic proteases release cobalamin from the haptocorrin-B12 complex and from other proteins containing protein-bound B12 that have been ingested. Following this, the binding of cobalamin to a second glycoprotein, intrinsic factor, promotes its uptake by terminal ileum mucosal cells by a process called cubilin/ AMN receptor-mediated endocytosis. After absorption into enterocytes, intrinsic factor is broken down in the lysosome, and cobalamin is then released into the bloodstream. The transporter ABCC1, found in the basolateral membrane of intestinal epithelial and other cells, exports cobalamin bound to transcobalamin out of the cell . Cyanocobalamin then passes through the portal vein in the liver, and then reaches the systemic circulation. The active forms of cyanocobalamin are methylcobalamin and adenosylcobalamin

DEFICIENCY

With age, it can become harder to absorb this vitamin. It can also happen if you have had weight loss surgery or another operation that removed part of your stomach, or if you drink heavily.

You may also be more likely to develop vitamin B12 deficiency if you have:

• Atrophic gastritis, in which your stomach lining has thinned
• Pernicious anemia, which makes it hard for your body to absorb vitamin B12
• Conditions that affect your small intestine, such as Crohn's disease, celiac disease, bacterial growth, or a parasite
• Immune system disorders, such as Graves' disease or lupus
• Been taking certain medications that interfere with the absorption of B12. This includes some heartburn medicines including proton pump inhibitors (PPIs) such as  rabeprazole, omeprazole, esomeprazole,, lansoprazole and pantoprazole; H2 Blockers such as cimetidine, famotidine and ranitidine; and certain diabetes medicines such as metformin.

·       Symptoms of Vitamin B12 Deficiency

·         Weakness, tiredness, or lightheadedness.

·         Heart palpitations and shortness of breath.

·         Pale skin.

·         A smooth tongue.

·         Constipation, diarrhea, loss of appetite, or gas.

·         Nerve problems like numbness or tingling, muscle weakness, and problems walking.

·         Vision loss.

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