Vitamin B12 is a nutrient that helps keep the body's nerve and blood cells healthy and helps make DNA, the genetic material in all cells. Vitamin B12 helps prevent anemia that makes people tired and weak. Involved in the metabolism of single-carbon fragments. Essential for biosynthesis of nucleic acids and nucleoproteins. Role in metabolism of nervous tissue. Involved with folate metabolism. Related to growth.
Vitamin B12 is synthesized by bacteria, but the vitamin produced from the microflora in the colon is not absorbed. Food of plant origin contain the vitamin only through contamination or bacterial synthesis.
Slowly destroyed by acid, light and oxidation.
Dietary reference intakes of Vitamin B12
Infants 0.4-0.5 mcg/day
Children 0.9-1.8 mcg/day
Adolescents 2.4 mcg/day
Adults 2.4 mcg/day
Pregnant 2.6 mcg/day
Lactating 2.8 mcg/day
Vitamin B12 content of selected foods
Liver, beef, 3.5 oz (71 mcg)
Clams, canned, 3 oz (84 mcg)
Oysters, raw, 6 medium (16.6 mcg)
Crab, raw, 3 oz (10 mcg)
Tuna, canned in water, 3 oz (2.5 mcg)
Halibut, baked, ½ filet (2.2 mcg)
Cottage cheese, 1 cup (1.6 mcg)
Yogurt, 8 oz (1.1 mcg)
Symptoms of Vitamin B12 deficiency
Progressive neuropathy (numbness, tingling and burning of the feet, stiffness and generalized weakness of the legs)
A lemon-yellow tint to the skin
A smooth, beefy, red tongue
The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods.