Significance and sources of cyanocobalamin Domina Petric, MD

Significance Vitamin B12 is synthesized by bacteria. It is found in the tissues of animals, which require the vitamin for critical functions in cellular division and growth. Some animal tissues can store the vitamin in very appreciable amounts that are sufficient to meet the needs of the organism for long periods (even years) of deprivation. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Significance The vitamin is not found in foods derived from plants: vegetables, grains and fruits do not contain vitamin B12. Humans that consume strict vegetarian diets (vegans) are very likely to have suboptimal intakes of vitamin B12. Deficiency of vitamin B12 leads to anemia and peripheral neuropathy. Low vitamin B12 status is relatively prevalent in eldery people. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Distribution in foods Because the synthesis of vitamin B12 is limited almost exclusively to bacteria, the vitamin is found only in foods that have been bacterially fermented and those derived from the tissues of animals that have obtained it from their ruminal or intestinal microflora, ingesting it either with their diet or coprophagously. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Distribution in foods The richest food sources of vitamin B12 are dairy products, meats, eggs, fish and shellfish. The principal vitamers in foods are methylcobalamin, deoxyadenosylcobalamin and hydroxycobalamin. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Distribution in foods Human milk contains 260-300 pM of vitamin B12, almost exclusively bound to an R-protein, which declines to only half that level after the first 12 weeks of lactation. Breast milk vitamin B12 levels of women consuming strict vegetarian diets are less than those of women consuming mixed diets, and tend to be inversely correlated with the length of time on the vegetarian diet. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Distribution in foods Infant urinary methylmalonic acid levels increase, indicating vitamin B12 deficiency at maternal milk vitamin B12 concentrations less than about 360 pM. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Distribution in foods Some algae and other plants (peas, beans) may also be able to synthesize small amounts of vitamin B12-like compounds. Foods derived from such sources have no value as sources of the vitamin. Fermented soy or rice products do not contain significant amounts of vitamin B12. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Meats Meat Vitamin B12 μg/100 g Beef 1,94-3,64 Beef brain 7,83 Beef kidney 38,3 Beef liver 69-122 Chicken 0,32 Chicken liver 24,1 Ham 0,8 Pork 0,55 Turkey 0,379 November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Diary products and eggs Diary products/eggs Vitamin B12 μg/100 g Milk 0,36 Cheeses 0,36-1,71 Yogurt 0,06-0,62 Whole eggs 1,26 Egg whites 0,09 Egg yolk 9,26 November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Fish and sea food Fish/sea food Vitamin B12 μg/100 g Herring 4,3 Salmon 3,2 Trout 7,8 Tuna 2,8 Clams 19,1 Oysters 21,2 Lobster 1,28 Shrimp 1,9 November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Stability Vitamin B12 is very stable in both crystalline form and aqueous solution. High levels of ascorbic acid have been shown to catalyze the oxidation of vitamin B12 in the presence of iron to forms that are poorly utilized. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Bioavailability Bioavailability of the vitamin in foods generally appears to be moderate. Studies have found that about 25-65% of the vitamin in eggs, meats and fish is absorbed. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Bioavailability Bioavailability falls off rapidly at intakes (>2 mg/day) exceeding those sufficient to saturate the active transport mechanism for active transport across the gut, as incremental enteric absorption of the vitamin depends on diffusion, a process with no greater than 1% efficiency. About 1% of the vitamin is absorbed from vitamin B12 supplements. November 21, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

Literature Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. November 21, 2018