1. MargiAnne Isaia, MD MPH Advanced Nutrition Vitamin B12

2. VITAMIN B12 Cobalamin - the term used for corrinoids exhibiting the biological activity of Vitamin B12 Cyanocobalamin vitamin B12 corrinoid with a cyano - ligand (CN) at the beta position of the Cobalt (Co) atom Cobalt - centered corrin ring synthesized by bacteria (in humans: bacteria in the colon synthesizes the vitamin B12, but it is not available because the absorption is at the terminal ileum and requires Intrinsic Factor binding)  Position above the plane of the corrin ring may be occupied by: - (CN) in cyanocobalamin (free, supplement, chemically synthesized) - hydroxy-ligand in hydroxycobalamin (free, supplement) - methyl group in methylcobalamin (coenzyme) - 5’-deoxyadenosyl group in adenosylcobalamin (coenzyme) VITAMIN B12

3. Cobalt-centered Corrin ring (CN) attached to Chorrin Cyanocobalamin VITAMIN B12 STRUCTURE VITAMIN B12

4. B12 METABOLISM Occurrence in: - food containing Vitamin B12 - the vitamin is bound to protein - supplements and enriched products - the vitamin is in the crystalline or free form Protein-bound B12 – released as free V B12 by gastric acidification and peptic digestion Free VB12 attaches to salivary R-binder (Haptocorrin Hc) Gastric parietal cells secrete Intrinsic Factor (IF) Both R-binder and IF are glycoproteins Pancreatic enzymes hydrolyze the R binders in the proximal small intestine; Once released, B 12 binds to IF VITAMIN B12

5. ABSORPTION AND TRANSPORT IF-B12 complex attaches to receptors on the brush border in the terminal ileum in the presence of ionic Calcium and pH>6 Endocytosis of B12-IF complex in the gut mucosa B12 - released in enterocyte - enters portal blood – it attaches to Transcobalamin II (TC II), a transport protein Absorption is dose dependent: maximum absorbed/day by IF receptors is 5  g large doses are absorbed by diffusion Blood transport proteins: Haptocorrin 70 – 80% Transcobalamin (TC II) 20-30 % Target cells: receptor mediated endocytosis of TC II Storage form: Transcobalamin I (TC I) 80% of vitamin B12 Stores adult: 2-3 mg (may be as low as 300  g) Excretion via bile – 1  g/day - reabsorption in the entero-hepatic circulation 50% of excreted vitamin VITAMIN B12

6. Absorption from food requires normal function of stomach pancreas small intestine 1% can be absorbed by passive diffusion VITAMIN B12

7. COBALAMIN ABSORPTION FROM A SINGLE ORAL DOSE GIVEN TO PERSONS WITH NORMAL ABSORPTION AND TO PERSONS WITHOUT IF (PERNICIOUS ANEMIA) Oral dose% absorption Normal * % absorption P Anemia** 0.25 mcg 0.19 mcg (75%)--- 1 mcg0.56 mcg (56%)0.02 mcg (2%) 2 mcg0.92 mcg (46%)--- 3 mcg---0.08 mcg (3%) 5 mcg1.4 mcg (28%)--- 10 mcg 1.6 mcg (16%)0.2 mcg (2%) 50 mcg1.5 mcg (3%)0.5 mcg (1%) 100 mcg ---1.8 mcg (1.8%) 500 mcg ---6 mcg (1.2%) % absorption Normal* – amount absorbed by IF mediated and passive processes % absorption P Anemia**- amount absorbed by passive process only 1 mcg = 1 m g VITAMIN B12

8. VITAMIN B12 BIOCHEMISTRY Two important metabolic reactions (Vitamin B12 as coenzyme) - mitochondrial reaction requiring 5’ deoxyadenosylcobalamin for MethylMalonyl CoA mutase which converts MethylMalonyl CoA to Succinyl CoA (odd chain FFA metabolism) - cytosolic reaction requiring methyl-cobalamin for Methionine synthase which converts Homocysteine to Methionine (folate –dependent metabolism of Homocysteine) VITAMIN B12

9. VITAMIN B12 BIOCHEMISTRY VB12 coenzyme for Methylmalonyl CoA mutase Involved in production of energy from fats and proteins. Succinyl CoA required for Hemoglobine synthesis Methylmalonyl CoA mutase VITAMIN B12

10. VB12 as coenzyme for Methionine synthase a folate-dependent enzyme (Methionine required for S-Adenosyl Methionine a methyl group donor used in methylation reactions ) Vitamin B12 Biochemistry VITAMIN B12

11. MEASUREMENT OF VITAMIN B12 STATUS Evaluation of the nutritional status by: Static markers Total serum B12 concentration total of Haptocorrin and Transcobalamin protein-bound fractions Deficient values < 200 pg/ml or < 148 pmol/L Serum Holotranscobalamin (holo TC) concentration reflects recent Vitamin B12 malabsorption and negative balance Functional markers Methylmalonic Acid (MMA) serum and urinary MMA ( holoTC+ MMA, storage depletion and functional B12 deficiency) Homocysteine (Hcy) total plasma Homocysteine not reliable by itself: It is increased in Folic Acid deficiency also. Hematological tests: MCV VITAMIN B12

12. CAUSES OF VITAMIN B12 DEFICIENCY Inborn errors of metabolism Dietary deficiency: - inadequate dietary intake (poverty) - strict vegetarian diet (vegan) Malabsorption = the most important cause in: chronic gastritis, atrophic gastritis (10-30%) over 60 years, total or partial gastrectomy, ileal resection, Crohn’s disease, severe pancreatitis, tropical and non-tropical sprue, HIV, parasites, several prescription drugs (Neomycin, Metformin, Proton Pump Inhibitors, Cytotoxic drugs), Chronic alcohol abuse *More than 10-15 % of population over 50 years of age - VB12 deficiency (decreased HCl secretion) VITAMIN B12

13. CLINICAL EFFECTS OF VITAMIN B12 DEFICIENCY - Megaloblastic Anemia - Neurological symptoms (only in 25 % cases associated with Megaloblastic Anemia) Alzheimer’s Disease, vascular dementia - Depression - Gastro-intestinal symptoms (Moller – Hunter – Glossitis) - Cardiovascular disease (increased levels of Hcy) VITAMIN B12

14. FoodServing Vitamin B 12 (mcg) Clams (steamed)3 ounces84.0 Mussels (steamed) 3 ounces20.4 Crab (steamed)3 ounces8.8 Salmon (baked)3 ounces2.4 Rockfish (baked)3 ounces1.0 Beef (cooked)3 ounces2.1 Chicken (roasted) 3 ounces0.3 Turkey (roasted)3 ounces0.3 Egg (poached)1 large0.6 Milk (skim)8 ounces0.9 Brie (cheese)1 ounce0.5 VITAMIN B12 IN FOOD SOURCES VITAMIN B12

15. VITAMIN B12 IN FOOD SOURCES Only bacteria can synthesize vitamin B 12 Vitamin B 12 is present in animal products meat, poultry, fish (including shellfish) to a lesser extent milk Not generally present in plant products or yeast Fresh pasteurized milk contains 0.9 mcg per cup important source of vitamin B 12 for some vegetarians VB12 supplementation Vegans need supplemental vitamin B 12 to meet their requirements (no problem for Indian vegans: poor sanitation) Individuals over the age of 50 should obtain their vitamin B 12 in supplements or fortified foods like fortified cereal VITAMIN B12

16. . * vitamin B12 intake from fortified foods or supplements in age-related malabsorption RECOMMENDED DIETARY ALLOWANCE (RDA) FOR VITAMIN B12 Life Stage Age Males (mcg/day) Females (mcg/day) Infants 0-6 months 0.4 (AI) AI0.4 (AI) Infants 7-12 months 0.5 (AI) Children 1-3 years 0.9 Children 4-8 years 1.2 Children 9-13 years 1.8 Adolescents 14-18 years 2.4 Adults 19-50 years 2.4 Adults 51 years and older 2.4* Pregnancy all ages - 2.6 Breast-feeding all ages - 2.8 VITAMIN B12

17. DIETARY REFERENCE INTAKE IN SEVERAL COUNTRIES (age > 15) NNR* DRI** UK*** SCF**** D-A-CH***** Vitamin B12 (mg/day) 2.0 2.4 1.5 1.4 3.0 Folate (mg/day) 300 400 200 200 400 NNR* Nordic Nutrition Recommendation 2004 DRI** Dietary Reference Intake 1997 (USA, Canada) UK*** Dietary Reference Value, GB, 1991 SCF**** Scientific Committee for Food of EU 1992 D-A-CH***** Germany – Austria – Switzerland (2004) VITAMIN B12

18. RECOMMENDATIONS (Linus Pauling Institute Oregon State University) Daily intake 6-30 mcg of VB12 in a easily absorbed form Higher doses if taking medication which interfere absorption Adults over 50 y supplements: 100-400 mcg/day In supplements Vitamin B12 is not bound to protein, IF still available, Absorption is not as reduced as in Pernicious Anemia VITAMIN B12

19. VITAMIN B12 STATUS AND HOMOCYSTEINE Studies in Austria comparing Vitamin B12, Homocysteine and Folate for omnivores, vegetarians, vegans Parameters to assess the prevalence of B12 deficiency (in %) B12 148 pmol/L Homocysteine 12  mol/L Folate 6.7 nmol/L RESULTS: Depending on the cutoff for V B12 level, there are different levels of deficiency B12 -Omnivores better results comparing with the vegetarians Homocysteine – increased in vegetarians, even with normal folate level Folate –normal levels for vegetarians and vegans Folate and Vitamin B12 have influence on Homocysteine level In Austria: small percentage of VB12 deficiency (for vegans 2.4%) no Megaloblastic Anemia VITAMIN B12

20. VITAMIN B12 STATUS AND HOMOCYSTEINE IN DIFFERENT STUDIES Mean serum B12 is generally lower (in some studies significantly lower) in vegetarians and vegans than in non-vegetarians Mean serum B12 is generally lower in vegans (strict vegetarians) than in moderate vegetarians( LV, LOV) Vegans and vegetarians are more often B12 deficient than non-vegetarians Mean plasma Homocysteine concentration is higher in vegetarians than in non-vegetarians Mean plasma Homocysteine concentration is higher in vegan than in vegetarians Mean plasma folate concentration is frequently higher in vegans than in vegetarians and non-vegetarians VITAMIN B12

21. CONCLUSIONS FROM PUBLISHED DATA:  Vitamin B12 status needs to be improved in order to minimize the risk of Hyper Homocysteinemia  Vitamin B12 and B2 may need attention in the strict vegetarian diet; Vitamin B6 status appeared to be independent of diet form  Vitamin B12 intake and mean plasma B12 were lower in vegetarians than in non-vegetarians leading to increased plasma Hcy concentrations  Vegetarian children (excluding vegans) have normal serum concentration of Hcy, folate, and Vitamin B12. In order to prevent deficiency, close monitoring of vegetarian children (especially on a vegan diet) is important to make sure that they receive adequate quantities of nutrients needed for healthy growth. VITAMIN B12

22. REFERENCES 5 ICVN Shils M et al, Modern Nutrition in Health and Disease, 10 th Edition www. Pubmed.org VITAMIN B12

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