Why is Vitamin B-12 important? (Cobalamin and other forms)

Take home message
  • Diet, inability to break the B12-Protein bond, or inadequate IF (intrinsic factor) may result in a B12 deficiency.  The deficiency can result in anemia, non-reversible neural damage, and other problems.
  • B12 is water soluble, the excess is eliminated, and there is not an upper limit.
  • Microwaves inactive B12.  However, stovetop and oven heat do not inactivate it.
  • HHS recommends older adults obtain B12 from fortified cereals or vitamin supplements.
  • There is only enough IF for the absorption of about 2 mcg of B12.  However, the current thought is that if sufficient B12 is consumed, 1% to 56% of it can be absorbed without IF. About 56% of 2 mcg or 20% 50 mcg in a vitamin B12 supplement is absorbed. 
  • The B12 level can be determined from blood tests.
  • B12 is created by microbes and it is obtained only from animal products, fortified cereals, vitamin supplements, and injections. Milk and fish have the greatest bioavailable of B12.  Swiss cheese has more than other cheeses. 

For example,

B12 per oz Amt to obtain 2.4 mcg
Swiss .95 mcg 2.5 oz
Cheddar 0.24 mcg 10 oz

B12 RDA (recommended daily allowance)

0–6 months*0.4 mcg0.4 mcg
7–12 months*0.5 mcg0.5 mcg
1–3 years0.9 mcg0.9 mcg
4–8 years1.2 mcg1.2 mcg
9–13 years1.8 mcg1.8 mcg
14+ years2.4 mcg2.4 mcg2.6 mcg2.8 mcg

NIH list of some of the B12 sources
FoodMicrograms (mcg)
per serving
Percent DV*
Clams, cooked, 3 ounces84.11,402
Liver, beef, cooked, 3 ounces70.71,178
Breakfast cereals, fortified with 100% of the DV for vitamin B12, 1 serving6.0100
Trout, rainbow, wild, cooked, 3 ounces5.490
Salmon, sockeye, cooked, 3 ounces4.880
Trout, rainbow, farmed, cooked, 3 ounces3.558
Tuna fish, light, canned in water, 3 ounces2.542
Cheeseburger, double patty and bun, 1 sandwich2.135
Haddock, cooked, 3 ounces1.830
Breakfast cereals, fortified with 25% of the DV for vitamin B12, 1 serving1.525
Beef, top sirloin, broiled, 3 ounces1.423
Milk, low-fat, 1 cup1.218
Yogurt, fruit, low-fat, 8 ounces1.118
Cheese, Swiss, 1 ounce0.915
Beef taco, 1 soft taco0.915
Ham, cured, roasted, 3 ounces0.610
Egg, whole, hard boiled, 1 large0.610
Chicken, breast meat, roasted, 3 ounces0.35


National Institutes of Health, Vitamin B12 Health Professional, US Dept of Health and Human Services (HHS), February 2016

National Institutes of Health, Vitamin B12 Consumer, US Dept of Health and Human Services (HHS), June 2011

Whitney, Ellie and Sharon Rady Rolfes.  Understanding Nutrition, Cengage Learning, 2016