Vitamin B12 – What Is It?

Vitamin B12Vitamin B12 is also known as cyanocobalamin, which is the free vitamin.  It is the largest and most complex of the vitamins.  There are also two coenzymes forms.  The common element in these three compounds is cobalt, hence the “cobal-“ part of the word.

Vitamin B12 is absorbed at the very end of the small intestine (ileum) with the help of a compound called intrinsic factor.  Only about 50% of vitamin B12 is absorbed from food.  Between 50-90% of this vitamin is stored in the liver (2-4 grams).  Unlike most water-soluble vitamins, only a little of this vitamin is excreted.

What Does It Do?

Vitamin B12 is needed by every cell in our bodies.  Generally, it assists in energy production, DNA synthesis and regulation, and fatty acid synthesis.  Specifically, it associates with coenzymes to move one-carbon groups from one compound to another.  Vitamin B12 also helps to recycle folate coenzymes.  Further, this vitamin plays a role in the nervous system, but researchers aren’t exactly sure how.

Where Can You Find It?

Vitamin B12 foodsVitamin B12 is a little different than most vitamins.  This vitamin is created solely by bacteria, fungi, and algae.  Animals ingest these organisms when they graze, or they are synthesized by symbiotic bacteria in their stomachs (rumen).  So, when we eat those animals, we benefit by obtaining this vitamin.  Plants do not create vitamin B12.  Therefore, the best way to obtain the daily requirements for vitamin B12 is to eat meat and seafood.  Because this is such an important vitamin, the U.S. mandated that it be added to fortified foods.

Good sources of vitamin B12 include beef liver, clams, oysters, turkey, Brewer’s yeast, lobster, fortified breakfast cereals, and fortified grain products.  Smaller amounts can be found in milk, eggs, and ham.   Beef liver, by far, has the most vitamin B12 per ounce.

For those of you who are vegetarians, make sure you take a supplement containing vitamin B12 daily so you do not become deficient in this important vitamin.

How Much Do You Need?

The RDAs for vitamin B12 is shown below: 



Upper   Limit

Infants and children
0-6 months

0.4   mcg

7-12 months

0.5   mcg

1-3 years

0.9   mcg

4-8 years

1.2   mcg

9-13 years

1.8   mcg

Adolescents, 14-18 years

2.4   mcg

Adults, 19+

2.4   mcg


2.6   mcg


2.8   mcg

What Happens If You Don’t Get Enough?

Deficiencies of vitamin B12 occur two ways – through disorders that result in malabsorption of the vitamin, or from not obtaining enough in the diet.

Symptoms-of-AnemiaThe most well-known vitamin B12 deficiency disorder is pernicious anemia.  The word “pernicious” means “leading to death.”  This is a genetic disease that leads to the destruction of the cells in the stomach (parietal cells) that produce intrinsic factor, which is necessary for vitamin B12 absorption.  Since folate and vitamin B12 work together, this disease is sometimes mistaken as a folate deficiency.  As with folate deficiency, megaloblasts can be seen in the blood and the deficiency can interfere with normal DNA synthesis.  Common symptoms include anemia, fatigue, depression, nausea, gastrointestinal issues, weight loss, swollen tongue (glossitis), brittle nails, proprioception (the body’s sense of position in relation to its surroundings), memory changes, difficulty walking, and low or high blood pressure.  In severe cases, it can result in congestive heart failure, spinal cord degeneration, and sensory loss.

General dietary deficiencies can result in all of the above symptoms as well.  As the deficiency worsens, it can lead to disorientation, dementia, and visual disturbances.

Conditions that affect nutrient absorption can also lead to a deficiency of this vitamin.  These include HIV/AIDS, older age (due to reduced gastric secretions), Crohn’s disease, IBS (intestinal bowel syndrome), and certain weight loss bypass surgeries.

What Happens If You Take Too Much?

There is no Tolerable Upper Limit for vitamin B12.  Mega-doses are used to treat pernicious anemia and no adverse side effects have been noted.

Bottom Line

The best way to consume any nutrient in order to avoid under-consumption is to consume a wide variety of foods, in a wide variety of colors, and eat according to MyPlate.

Until next time, remember that… there are no excuses when it comes to your health!


One thought on “Vitamin B12 – What Is It?

  1. Excellent site. Lots of useful info here. I’m sending it to a few pals ans also sharing in delicious. And of course, thanks in your effort!

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