Sources of Vitamin B12

Food

Vitamin B12 is naturally found in animal products, including fish, meat, poultry, eggs, milk, and milk products. Vitamin B12 is generally not present in plant foods, but fortified breakfast cereals are a readily available source of vitamin B12 with high bioavailability for vegetarians [5,13-15]. Some nutritional yeast products also contain vitamin B12. Fortified foods vary in formulation, so it is important to read product labels to determine which added nutrients they contain.

Several food sources of vitamin B12 are listed in Table 2.

Table 2: Selected Food Sources of Vitamin B12 [13]

Food	Micrograms (mcg) per serving	Percent DV*
Liver, beef, braised, 1 slice	48.0	800
Clams, cooked, breaded and fried, 3 ounces	34.2	570
Breakfast cereals, fortified with 100% of the DV for vitamin B12, 1 serving	6.0	100
Trout, rainbow, wild, cooked, 3 ounces	5.4	90
Salmon, sockeye, cooked, 3 ounces	4.9	80
Trout, rainbow, farmed, cooked, 3 ounces	4.2	50
Beef, top sirloin, broiled, 3 ounces	2.4	40
Cheeseburger, double patty and bun, 1 sandwich	1.9	30
Breakfast cereals, fortified with 25% of the DV for vitamin B12, 1 serving	1.5	25
Yogurt, plain, 1 cup	1.4	25
Haddock, cooked, 3 ounces	1.2	20
Tuna, white, 3 ounces	1.0	15
Milk, 1 cup	0.9	15
Cheese, Swiss, 1 ounce	0.9	15
Beef taco, 1 taco	0.8	13
Ham, cured, roasted, 3 ounces	0.6	10
Egg, large, 1 whole	0.6	10
Chicken, roasted, ½ breast	0.3	6

*DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration (FDA) to help consumers determine the level of various nutrients in a standard serving of food in relation to their approximate requirement for it. The DV for vitamin B12 is 6.0 mcg. However, the FDA does not require food labels to list vitamin B12 content unless a food has been fortified with this nutrient. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet. The U.S. Department of Agriculture’s Nutrient Database Web site (http://www.nal.usda.gov/fnic/foodcomp/search/ [13]) lists the nutrient content of many foods and provides a comprehensive list of foods containing vitamin B12:
http://www.nal.usda.gov/fnic/foodcomp/Data/SR20/nutrlist/sr20w418.pdf.

Dietary supplements

In dietary supplements, vitamin B12 is usually present as cyanocobalamin [5], a form that the body readily converts to the active forms methylcobalamin and 5-deoxyadenosylcobalamin. Dietary supplements can also contain methylcobalamin and other forms of vitamin B12.

Existing evidence does not suggest any differences among forms with respect to absorption or bioavailability. However the body’s ability to absorb vitamin B12 from dietary supplements is largely limited by the capacity of intrinsic factor. For example, only about 10 mcg of a 500 mcg oral supplement is actually absorbed in healthy people [8].

In addition to oral dietary supplements, vitamin B12 is available in sublingual preparations as tablets or lozenges. These preparations are frequently marketed as having superior bioavailability, although evidence suggests no difference in efficacy between oral and sublingual forms [16,17].

Prescription medications

Vitamin B12, in the form of cyanocobalamin and occasionally hydroxocobalamin, can be administered parenterally as a prescription medication, usually by intramuscular injection [12]. Parenteral administration is typically used to treat vitamin B12 deficiency caused by pernicious anemia and other conditions that result in vitamin B12 malabsorption and severe vitamin B12 deficiency [12].

Vitamin B12 is also available as a prescription medication in a gel formulation applied intranasally, a product marketed as an alternative to vitamin B12 injections that some patients might prefer [18]. This formulation appears to be effective in raising vitamin B12 blood levels [19], although it has not been thoroughly studied in clinical settings.