Vitamin B12


Vitamin B12 Introduction

Another Vitamin B-compound that is essential to one’s overall health is Vitamin B12, or cobalamins. It is named after the metal cobalt because Vitamin B12 contains both the chemical characteristics of the metal and its unique color. Cobalamins is required for an assortment of functions located throughout the body. It is primarily stored in the liver and plays a key role in the intrinsic factor, or IF, before being released for absorption in the bloodstream. The IF is a substance which provides the body with the ability to absorb Vitamin B12 from the digestive system.

Cobalamins functions as a coenzyme and aids in the synthesis of DNA and RNA. These nucleic acids contain the makeup of genetic coding and genetic material(s). Vitamin B12’s primary, and most important, role is in the consistent regeneration of the folate coenzyme (THF). DNA synthesis would be dramatically affected is this regeneration did not take place. Cells in the body would be deficient. The maintenance of the central nervous system, and the growth and reproduction processes of our bodies would cease.

Vitamin B12 Food Sources

Cobalamins is also synthesized by bacteria in the colon. However, this source is inadequate in providing for our daily requirements of Vitamin B12.

Beef liver, cooked, 3 oz 60.0 1000
Fortified breakfast cereals, (100%) fortified), 3/4 c 6.0 100
Trout, rainbow, cooked, 3 oz 5.3 90
Salmon, sockeye, cooked, 3 oz 4.9 80
Beef, cooked, 3 oz 2.1 35
Fortified breakfast cereals (25% fortified), 3/4 c 1.5 25
Haddock, cooked, 3 oz 1.2 20
Clams, breaded and fried, 3/4 c 1.1 20
Oysters, breaded and fried, 6 pieces 1.0 15
Tuna, white, canned in water, 3 oz 0.9 15
Milk, 1 cup 0.9 15
Yogurt, 8 oz 0.9 15
Pork, cooked, 3 oz 0.6 10
Egg, 1 large 0.5 8
American Cheese, 1 oz 0.4 6
Chicken, cooked, 3 oz 0.3 6
Cheddar cheese, 1 oz 0.2 4
Mozzarella cheese, 1 oz 0.2 4


Vitamin B12 Uses

Supplementation with Vitamin B12 may provide our bodies with both short and long-term benefit. Cobalamins supplementation may be most important in the treatment of pernicious anemia. [2] This disease is associated with a dietary deficiency of the vitamin B12 and occurs when an intrinsic factor is absent (usually in the stomach). Anyone suffering from this disease may need supplementation of cobalamins for the remainder of his/her life.

Cobalamins has also been studied in the short term fertility in males. Research has shown that supplementation with Vitamin B12 may increase sperm count and motility. [3] Other short-term afflictions shown to be treated by cobalamins supplementation include; HIV, burn injuries, and osteoporosis. [4-6]

Long-term supplementation of Vitamin B12 may be most effective when combined with other B-complex vitamins, particularly B6 and B9. Of particular interest, is the long-term dietary cobalamin supplementation and the effect on homocysteine levels in the blood. Vitamin B12 is an important nutrient used in the conversion of the toxic amino acid homocysteine, to a tolerable form usable in the body. Elevated homocysteine levels are dramatically influenced by B-vitamin compounds and may increase the risk for developing chronic illnesses, including; heart disease, atherosclerosis, and impairments in cognitive functioning. [7-9]

Elevated levels of homocysteine have also been documented in individuals suffering from Alzheimer's disease. Research has indicated that individuals with improper dietary supplementation of Vitamin B12 are twice as likely to develop the Alzheimer’s, than those individuals with proper supplementation. [10]

Another area of study concerning post-menopausal women, showed that lower levels of vitamin B12 are paralleled to an increased incidence of breast cancer. [11] More research is necessary, but Vitamin B12 deficiency may also be linked to the formation of cataracts and psychological disorders; mainly depression.

Vitamin B12 Dosages

The RDA for Vitamin B12 was revised in 1998:

Ages 19+ 2.4 mcg 2.4 mcg
All ages 2.6 mcg 2.8 mcg

It is highly recommended that individuals over the age of 50 obtain the majority of cobalamins from fortified foods or supplementation. This is due to the ever increasing malabsorption rate of vitamins as we age. Because vegetarians exclude animal sources in their diets, it is also critical for these persons to supplement their diets with cobalamins or to increase intake of fortified foods containing B12.

Vitamin B12 Toxicities and Deficiencies

Vitamin B12 Deficiencies

Although, dietary deficiencies of Vitamin B12 take years to develop, they are among the most common of all nutrient deficiencies. Cobalamins deficiency is characterized by a lack of intrinsic factor, or the inability to absorb food. Symptoms include blood and nerve damage, fatigue, diarrhea, nervousness, flatulence, and shortness of breath. [12] Deficiencies are common in vegetarians and those suffering from gastrointestinal disorders or infections (e.g. tapeworm). The abovementioned disease of pernicious anemia is the number one ailment defining a B12 deficiency.

Vitamin B12 Toxicities

The Institute of Medicine has previously stated that “no adverse effects have [ever] been associated with excess vitamin B12 intake from food and supplements in healthy individuals.” [13] It may be safer to say that although overdose can occur, cobalamins supplementation has a low occurrence of toxicity. Signs of an overdose have only been studied in infants with rare genetic defects.


1. Clinical Nutrition Service, Warren Grant Magnuson Clinical Center, National Institutes of Health (NIH), NIH. Vitamin B12 December. 9. 2002.

2. Lederle FA. Oral Cobalamin for Pernicious Anemia: Back From the Verge of Extinction. J Am Geriatr Soc. Sep 1998; 46 (9): 1125-27

3. Sinclair S. Male infertility: nutritional and environmental considerations. Alt Med Rev. 2000;5(1):28-38.

4. Remacha AF, Cadafalch J. Cobalamin deficiency in patients infected with the human immunodeficiency virus. Semin Hematol. 1999;36:75–87.

5. De-Souza DA, Greene LJ. Pharmacological nutrition after burn injury. J Nutr. 1998;128:797-803.

6. Bunker VW. The role of nutrition in osteoporosis. Br J Biomed Sci. 1994;51(3):228-240.

7. Eikelboom JW, Lonn E, Genest J, Hankey G, Yusuf S. Homocyst(e)ine and cardiovascular disease: a critical review of the epidemiologic evidence. Ann Intern Med. 1999;131:363-375.

8. Lindeman RD, Romero LJ, Yau CL, Koehler KM, Baumgartner RN, Garry PJ. Serum homocysteine concentrations and their relation to serum folate and vitamin B12 concentrations and coronary artery disease prevalence in an urban, bi-ethnic community. Ethn Dis. 2003; 13(2):178-85.

9. Calvaresi E, Bryan J. B vitamins, cognition and aging: a review. J Gerontol B Psychol Sci Soc Sci. Nov 2001; 56(6): P327-39

10. Wang HX, Wahlin A, Basun H, Fastborn J, Winbald B, Fratiglioni L. Vitamin (B12) and folate in relation to the development of Alzheimer’s Disease. Neurology. May 2001; 56(9): 1188-94.

11. Wu K, Helzlsouer KJ, Comstock GW, Hoffman SC, Nadeau MR, Selhub J. A prospective study on folate, B12, and pxridoxal 5’- phosphate (B6) and breast cancer. Cancer Epidemiol Biomarkers Prev. 1999; 8(3): 209-17.

12. Herbert V. Vitamin B12 in Present Knowledge in Nutrition. 17th ed. Washington, DC: International Life Sciences Institute Press, 1996.

13. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes: Thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin, and choline. National Academy Press. Washington, DC, 1998.