Vitamin B12 
By Walter Sorochan

Posted May 22, 2012; updated November 10, 2021.  Disclaimer The information presented here is for informative and educational purposes only and is not intended as curative or prescriptive advice.

Introduction:  There is a lot of information about vitamin B12.  So much technical stuff that even an expert can get lost in all this information jungle.  This vitamin has become somewhat controversial with many persons perceiving getting this vitamin through intramuscular injection [ skin ] injections on the assumption that this procedure will provide them with more energy.   Some persons even claim that vitamin B12 helps them to lose body weight.  Another issue deals with vegetarians being deficient on the assumption that B12 is consumed solely from eating animal foods. 

According to the UK Vegan Society, the present consensus is that any B12 present in plant foods is likely to be unavailable to humans because B12 analogues can compete with B12 and inhibit metabolismWiki: Vit B12

Some critics of meat-eating and nutritionists cite that the human intestinal tract also contains B12-producing bacteria;  however, it is unclear whether this is in sufficient amounts for proper nutrition.  Wiki: Vit B12   So there is mis-information, lack of good information and controversy! 

Facilitator Sorochan tries to simplify all this extensive website information.  But you can go for more details in  Wiki: Vit B12  and referral articles. 

Body Functions: Vitamin B12 normally plays a significant role in the metabolism of every cell of the body, especially affecting the DNA synthesis and regulation, fatty acid synthesis and energy production.  Wiki: Vit B12  

What is Vitamin B12 ?

Vitamin B12 [ cobalamin ] is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement and a prescription medication. Vitamin B12 exists in several forms and contains the mineral cobalt, so compounds with vitamin B12 activity are collectively called "cobalamins".   Methylcobalamin and 5-deoxyadenosylcobalamin are the forms of vitamin B12 that are active in human metabolism.

Vitamin B12 dissolves in water. After the body uses this vitamin, leftover amounts leave the body through the urine.

Vitamin B12 is one of 8 B vitamins. All B vitamins help the body convert food (carbohydrates) into fuel (glucose), which is used to produce energy. These B vitamins, often referred to as B complex vitamins, also help the body use fats and protein. B complex vitamins are needed for healthy skin, hair, eyes, and liver. They also help the nervous system function properly.

Source Vitamin B12:

Ultimately, animals must obtain vitamin B12 directly or indirectly from bacteria, and these bacteria may inhabit a section of the gut which is posterior to the section where B12 is absorbed.  Scientists have assumed that the bacteria in the human gut were able to synthesize ample amounts  B12. 

Vitamin B12 is found in foods that come from animals, including fish and shellfish, meat (especially liver), poultry, eggs, milk, and milk products.  Eggs are often mentioned as a good B12 source, but they also contain a factor that blocks absorption. 

Vitamin B12, bound to protein in food, is released by the activity of hydrochloric acid and gastric enzyme protease in the stomach. When synthetic vitamin B12 is added to fortified foods and dietary supplements, it is already in free form and, thus, does not require this separation step. Free vitamin B12 then combines with intrinsic factor, a glycoprotein secreted by the stomach's parietal cells, and the resulting complex undergoes absorption within the distal ileum by receptor-mediated endocytosis. Approximately 56% of a 1 mcg oral dose of vitamin B12 is absorbed, but absorption decreases drastically when the capacity of intrinsic factor is exceeded (at 1–2 mcg of vitamin B12).   NIH: Supplements  

Nutritional yeast should not be relied upon as a source of B12 unless it is fortified.   Saccharomyces cerevisiae, a strain of nutritional yeast, often contains vitamin B12, either naturally occurring or as an additive.  Because nutritional yeast is often used by vegans, who usually need to supplement their diets with vitamin B12, there has been confusion about the source of the B12 in nutritional yeast. 

The best way to get vitamin B12 for human is still a mystery!

Medical uses

Vitamin B12 is used to treat vitamin B12 deficiency, cyanide poisoning, and hereditary deficiency of transcobalamin IIWiki: Vit B12

Injection and patches are sometimes used if digestive absorption is impaired, but there is evidence that this course of action may not be necessary with modern high potency oral supplements (such as 0.5 to 1 mg or more). Even pernicious anemia can be treated entirely by the oral route. Wiki: Vit B12

Vitamin B12 is used to treat vitamin B12 deficiency, cyanide poisoning, and hereditary deficiency of transcobalamin II.   It is also given as part of the Schilling test for detecting pernicious anemia.  Wiki: Vit B12

For cyanide poisoning, a large amount may be given intravenously, and sometimes in combination with sodium thiosulfate.   The mechanism of action is straightforward: the hydroxycobalamin hydroxide ligand is displaced by the toxic cyanide ion, and the resulting harmless B12 complex is excreted in urine.  In the United States, the Food and Drug Administration approved (in 2006) the use of hydroxocobalamin for acute treatment of cyanide poisoning.  Wiki: Vit B12

Recommended intake

The dietary reference intake for an adult ranges from 2 to 3 µg per day. Wiki: Vit B12

Deficiency: B12 deficiency is the cause of pernicious anemia.  In many cases, the cause of vitamin B12 deficiency is unknown.  NNIH: Supplements

Most vitamin B12 deficiency symptoms are actually folate deficiency symptoms. 

Deficiency Symptoms:  Vitamin B12 deficiency is characterized by megaloblastic anemia, fatigue, depression, poor memory, weakness, constipation, loss of appetite, and weight loss. Neurological changes, such as numbness and tingling in the hands and feet, can also occur. Additional symptoms of vitamin B12 deficiency include difficulty maintaining balance, depression, confusion, dementia, poor memory, and soreness of the mouth or tongue.  NIH: Supplements  However, these symptoms by themselves are too nonspecific to diagnose deficiency of the vitamin.  Wiki: Vit B12

Some people—particularly older adults, those with pernicious anemia, and those with reduced levels of stomach acidity (achlorhydria) or intestinal disorders—have difficulty absorbing vitamin B12 from food and, in some cases, oral supplements. As a result, vitamin B12 deficiency is common, affecting between 1.5% and 15% of the general population. In many of these cases, the cause of the vitamin B12 deficiency is unknown. Evidence from the Framingham Offspring Study suggests that the prevalence of vitamin B12 deficiency in young adults might be greater than previously assumed.  NIH: Supplements

Bacteria synthesizing B12: 

Neither plants nor animals are independently capable of synthesizing vitamin B12. Wiki: Vit B12  This contradicts the older belief that bacteria in the large intestine were able to synthesize B12.

Species from the following genera are known to synthesize B12: Acetobacterium, Aerobacter, Agrobacterium, Alcaligenes, Azotobacter, Bacillus, Clostridium, Corynebacterium, Flavobacterium, Micromonospora, Mycobacterium, Nocardia, Propionibacterium, Protaminobacter, Proteus, Pseudomonas, Rhizobium, Salmonella, Serratia, Streptomyces, Streptococcus and XanthomonasWiki: Vit B12

Industrial production of B12 is through fermentation of selected microorganisms.   Streptomyces griseus, a bacterium once thought to be a yeast, was the commercial source of vitamin B12 for many years.  Wiki: Vit B12

Storage in Body: 

The total amount of vitamin B12 stored in body is about 2–5 mg in adults. Around 50% of this is stored in the liver. Approximately 0.1% of this is lost per day by secretions into the gut, as not all these secretions are reabsorbed. Bile is the main form of B12 excretion; however, most of the B12 secreted in the bile is recycled via enterohepatic circulation.  Due to the extremely efficient enterohepatic circulation of B12, the liver can store several years’ worth of vitamin B12; therefore, nutritional deficiency of this vitamin is assumed to be rare.  Wiki: Vit B12


Vitamin B12 is provided as a supplement in many processed foods, and is also available in vitamin pill form, including multi-vitamins. Vitamin B12 can be supplemented in healthy subjects also by liquid, transdermal patch, nasal spray, or injection and is available singly or in combination with other supplements. It is a common ingredient in energy drinks and energy shots, usually at several times the minimum recommended daily allowance of B12.  Wiki: Vit B12

Due to its role in energy metabolism, vitamin B12 is frequently promoted as an energy enhancer and an athletic performance and endurance booster. These claims are based on the fact that correcting the megaloblastic anemia caused by vitamin B12 deficiency should improve the associated symptoms of fatigue and weakness. However, vitamin B12 supplementation appears to have no beneficial effect on performance in the absence of a nutritional deficit.  NIH: Supplements


The body’s ability to absorb vitamin B12 from dietary supplements is largely limited by the capacity of intrinsic factor.  Intrinsic factor is a chemical which is secreted by cells in your stomach and aids in the absorption of this vital nutrient.  Without intrinsic factor, your body cannot absorb vitamin B12.  For example, only about 10 mcg of a 500 mcg oral supplement is actually absorbed in healthy people.  NIH: Supplements     Grey: Intrisic factor

With the help of intrinsic factor, this amount increases to 56 percent of a 1 microgram dosage of B-12. However, Intrinsic factor has its limits. If you take dosages of B-12 that exceed the capacity of intrinsic factor -- between 1 and 2 micrograms -- absorption is decreased.   Grey: Intrisic factor

Co-Factor Impact:

A cofactor is a non-protein chemical compound that is bound to a protein and is required for the protein's biological activity. These proteins are commonly enzymes.  Cofactors can be considered "helper molecules" that assist in biochemical transformations. Vitamins and minerals [ cobalt ] can help each other and proteins in metabolic processes.   Wiki: Vit B12

An overlooked co-factor in vitamin B12 is homocysteine. HOMOCYSTEINE is a naturally occurring by-product of methionine metabolism in the body. Homocysteine accumulates in the body causing cell damage and the onset of major disease. This can happen when the biochemical transformation process is not working properly, usually due to lack of needed vitamins and minerals [ co-factors ] for the given homocysteine pathways.    Article by Jupp: Intrinsic factor & Homocysteine is no longer active.

Medical doctors Patrick Holford and Dr James Braly have written a book on the subject of homocysteine. They recommend an "H score" that is more important than your weight, your blood pressure or your cholesterol level. The H score is your most vital, preventable and reversible health statistic." and "Your Homocysteine level is a more accurate predictor than cholesterol of our risk of heart attack or stroke."  Article by Jupp: Intrinsic factor & Homocysteine is no longer active.

Get tested for vitamin B12 status:

So why aren't doctors looking at homocysteine ? They can. And YOU can ask your GP to do the blood test - a fasting plasma homocysteine. The Labs will give "normal levels" as 6.5 - 11.9mmol/L or even higher but Dr. Holford in his book recommends a level below 6. Article by Jupp: Intrinsic factor & Homocysteine is no longer active.

Final Word:  Taking vitamin B12 by itself as a supplement does very little to help your body. Reason ---- nutrients, including the B complex vitamins, work as a team with other vitamins, minerals and amino acids. The body needs over 200 co-factors to help body metabolic processes. These processes, in turn, may be regulated by genetic factors, many of which may be unknown at this time. We neglected humans need "much immediate research" on nutrition!


Grey Charis, "Vitamin B12 and Intrinsic Factor,", Jun 9, 2011.   Grey: Intrisic factor

Jupp Tessa, "Homocysteine unveiled," In a 2003 book "The H Factor" by Patrick Holford and Dr James Braly, MDs.  Article by Jupp: Intrinsic factor & Homocysteine is no longer active.

National Institutes of Health, "Dietary Supplement Fact Sheet: Vitamin B12," Office of Dietary Supplements,   NIH: Supplements

Wikipedia, "Co-factors,"   Wiki: co-factor

Wikipedia, "Vitamin B12,"  Wiki: Vit B12