Vitamin B12

Vitamin B12- definition, functions, absorption, storage, transportation, deficiency, pernicious anemia, relationship between vitamin B12 and folate deficiency, sign & symptoms, deficiency in case of maternal & child health care, RDA, sources, prevention and treatment.

1. Vitamin B 12 , also called cobalamin , is a water-soluble vitamin. It is one of eight B vitamins. It synthesized by only microorganisms and not by animals and plants. It was the last vitamin to be discovered. Functions: It is needed to absorb iron, Ca, and vitamin A. A key role in the normal functioning of the brain and nervous system via the synthesis of myelin ( myelinogenesis ). T he formation of red blood cells. It is involved in the metabolism of every cell of the human body, especially affecting DNA synthesis, fatty acid and amino acid metabolism. Vitamin B 12

2. The vitamin B 12 is present in the diet in a bound form to proteins. B 12 is liberated by the enzymes (acid hydrolases ) in the stomach. The dietary source of B 12 is known as extrinsic factor of Castle. The stomach secretes a special protein called intrinsic factor (IF). IF generally forms a dimer , binds strongly with 1 or 2 moles of vitamin B 12 . This binding protects vitamin B 12 against its uptake and use by bacteria. The cobalamin-lF complex travels through the gut. The complex binds to specific receptors on the surface of the mucosal cells of the ileum . The binding of the complex and Metabolism (How it works?)

3. entry of B 12 into the mucosal cells is mediated by Ca 2+ ions. In the mucosal cells, B 12 is converted to methylcobalamin . It is then transported in the circulation in a bound form to proteins namely transcobalamins (TC-|, TC- ll ). Methylcobalamin which is in excess is taken up by the liver, converted to deoxyadenosyl B 12 and stored in this form. lt is believed that liver can store about 4-5 mg, an amount sufficient to meet the body requirements of B 12 for 4-6 years. Metabolism (How it works?)

4. Metabolism (How it works?) Figure : Metabolism of vitamin B 12 , ( lF-lntrinsic factor; TC- Transcobalamins (TC-l, TC- ll ).

5. Vitamin B 12 deficiency may develop if have: Atrophic gastritis, in which stomach lining has thinned. 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. Because plants do not synthesize vitamin B 12 , individuals who consume diets completely free of animal products (vegan diets) are at risk of vitamin B 12 deficiency . Vitamin B 12 Deficiency (Why develop in our body?)

6. Vitamin B 12 deficiency may develop if have: With age, it can become harder to absorb vitamin B 12 . Elderly people over age 60 who produce less stomach acid, thereby increasing their probability of B 12 deficiencies. It can also happen if have had weight loss surgery or another operation that removed part of stomach, if drink heavily, or if have taken acid-reducing medications for a long time. Pernicious anemia, which makes it hard for body to absorb vitamin B 12 . It is characterized by low hemoglobin levels, decreased number of erythrocytes and neurological manifestations. Vitamin B 12 Deficiency (Why develop in our body?)

7. One or more of the following causes are attributed to the occurrence of pernicious anemia. 1. Autoimmune destruction of gastric parietal cells that secrete intrinsic factor. In the absence of IF, vitamin B 12 cannot be absorbed. 2. Hereditary malabsorption of vitamin B 12 . 3. Partial or total gastrectomy -these individuals become intrinsic factor deficient. 4. Insufficient production of IF and/or gastric HCl , occasionally seen in older people. 5. Dietary deficiency of B 12 , is seen among the strict vegetarians of low socioeconomic group in the developing countries (India, Srilanka , etc.). From the foregoing discussion, it is clear that pernicious anemia is more a disease of the stomach than due to the deficiency of vitamin B 12 . Vitamin B 12 Deficiency (Why develop in our body?)

8. Folic acid deficiency Vitamin B12 Relationship Between Vit - B 12 and Folate Deficiency Demyelination Neurologic Disease Subacute combined degeneration Reduction in DNA synthesis ( thyrimidine synthesis) relative to RNA synthesis ( uracil levels normal) results in unbalanced cell growth Macrocytes are large, fully hemoglobinized RBC’sthat result from omitted cell divisions during erythropoeisis Inadequate DNA synthesis affects rapidly growing tissues(e.g. tongue) Megaloblastic anemia Glossitis

9. Vitamin B 12 deficiency ( Sign & Symptoms) If you have vitamin B 12 deficiency, you could become anemic. A mild deficiency may cause no symptoms. But if untreated, it may lead to symptoms such as: 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 Mental problems like depression, memory loss, or behavioral changes 

10. Vitamin B 12 Deficiency in case of Maternal & Child Health Care A vitamin B 12 deficiency is associated with increased risk for several adverse pregnancy outcomes for both mother and fetus. These risks include- neural tube defects, intrauterine growth retardation, preeclampsia and early miscarriage. Even more frighteningly, the neurological and developmental delays in babies that can be caused by a vitamin B 12 deficiency are irreversible. According to the World Health Organization, vitamin B 12 is just as important in preventing neural tube and other neurological defects in infants.

11. The average recommended amounts, measured in micrograms (mcg), vary by age: Infants up to age 6 months: 0.4 mcg Babies age 7-12 months: 0.5 mcg Children age 1-3 years: 0.9 mcg Kids age 4-8 years: 1.2 mcg Children age 9-13 years: 1.8 mcg Teens age 14-18: 2.4 mcg Pregnant: 2.6 mcg Breastfeeding: 2.8 mcg Adults: 2.4 mcg RDA Sources: https ://www.webmd.com/diet/vitamin-b12-deficiency-symptoms-causes

12. Animal sources Vitamin B 12 comes primarily from animal-derived foods. Animal sources include clams, organ meats (especially liver) from lamb, veal, beef, and turkey, fish eggs, mackerel, and crab meat. Plant sources Plant foods do not contain vitamin B 12 except when contaminated by microorganisms. Fortified food sources Foods for which B 12 -fortified versions are widely available include breakfast cereals, fruit & vegetable juices, soy products, tofu, non-dairy milk , plant-based meats, energy bars, and nutritional yeast. Supplementary sources Tablets or syrups ( Cyanocobalamin or Methylcobalamin ) Sprays & drops Injections (mostly Hydroxycobalamin ) Sources

13. Most people can prevent vitamin B 12 deficiency by eating enough meat, poultry, seafood, dairy products, and eggs. If have pernicious anemia or have trouble absorbing vitamin B 12 , need shots of vitamin B 12 at first. May need to keep getting these shots of vitamin B 12 , take high doses of a supplement, or get it nasally after that. If don’t eat animal products, changediet to include vitamin B 12 fortified grains, a supplement or B 12 injections, or a high-dose oral vitamin B 12 if deficient. Older adults who have a vitamin B 12 deficiency should take a daily B 12 supplement or a multivitamin that contains B 12 . For most people, treatment resolves the problem. But, any nerve damage that happened due to the deficiency could be permanent. Treatment & Prevention