August 31, 2020

Where is B12 Absorbed?

Vitamin B12 is one of the most important nutrients for human health, but our body can’t synthesize the vitamin itself, so vitamin B12 must be consumed through our food sources. Vitamin B12 is a water-soluble vitamin primarily found in animal products such as meats and dairy products, putting vegans or those who consume a vegan diet at risk of vitamin B12 deficiency.

On top of this, it’s also critically important that our bodies be able to actually absorb enough B12 to meet the body’s needs. Several factors can impact the absorption of vitamin B12, which we'll discuss below in addition to reiterating why having the right amount of vitamin B12 in your system is so important. 


Why is vitamin B12 important?

Vitamin B12 is an essential vitamin that our bodies cannot function properly without (1). Vitamin B12, also known as cobalamin, has an impact on many important functions and processes in the body, but we cannot manufacture it on our own. Therefore, our bodies depend on dietary vitamin B12.

However, consuming enough B12 is only one part of the equation. We must also be able to readily absorb the vitamin in order to feel its effects and receive the numerous health benefits it offers. Vitamin B12 plays a role in making DNA and keeping the blood cells and nerves healthy and functioning properly. If we do not consume and absorb enough vitamin B12 to meet our body's demand, we may experience uncomfortable and potentially dangerous symptoms as the result of the cobalamin deficiency. 


Where is vitamin B12 absorbed?

Like many vitamins and minerals, vitamin B12 is absorbed in the small intestine. However, before it makes its way there, the body must properly prepare it to make sure it gets absorbed efficiently (2). 

If in its "free" form, i.e. not a protein, it binds to a protein called transcobalamin/transcobalamin II in the saliva and in mucosal cells, which protects the B12 from being broken down by stomach acid. 

If in its protein form, the B12 actually needs to be broken down before it can be absorbed. The parietal cells ultimately provide pepsin, which helps to cleave the B12 and put it in its absorbable form. 

Then, the absorbable version of vitamin B12 is absorbed in the distal ileum, which is the last part of the small intestine shortly before it connects to the large intestine (3). In order for absorption to occur, vitamin B12 must be combined within a protein produced by the stomach called intrinsic factor. If the body does not produce intrinsic factor or does not have enough of the protein, vitamin B12 cannot bind to it in the duodenum nor be absorbed, and it moves through the intestines and is then excreted as part of the stool. Intrinsic factor deficiency is one of the numerous causes of inadequate absorption of vitamin B12.


What causes inadequate absorption of vitamin B12?

Vitamin B12 deficiency can be the result of inadequate consumption of the vitamin, inadequate absorption of B12, or inadequate storage of the vitamin. However, most people experience vitamin B12 deficiency as a result of an absorption issue. As noted above, some people do not produce adequate amounts of intrinsic factor for a number of reasons. Intrinsic factor production can be limited by an autoimmune disease that attacks and destroys the stomach cells responsible for producing the protein, or it can be caused by the surgical removal of the portion of the stomach responsible for the production of intrinsic factor. When severe vitamin B12 deficiency is caused by a lack of intrinsic factor, a type of anemia called pernicious anemia results, which is often treated by cyanocobalamin, a man-made version of vitamin B12, or methylcobalamin, another form of vitamin B12. 

Other risk factors for vitamin B12 absorption issues include (3):

  • Overgrowth of bacteria in the small intestine
  • Inflammatory bowel disease that damages the portion of the small intestine responsible for the absorption of vitamin B12
  • AIDS
  • Use of medications including proton pump inhibitors and metformin
  • Decreased stomach acidity, particularly among older adults
  • Malabsorption disorders such as celiac disease and some disorders of the pancreas
  • Fish tapeworm infection
  • Surgery removing the portion of the small intestine where vitamin B12 is absorbed
  • Repeated exposure to nitrous oxide 


What health benefits are associated with vitamin B12?

Because vitamin B12 plays such an important role in a number of critical body functions and processes, consuming and absorbing enough of the vitamin is critical. Health benefits provided by vitamin B12 are described below (1).


Supports Bone Health

When consumed and absorbed in the right amounts, vitamin B12 helps support bone health and the formation of strong bones. Reduced bone mineral density has been linked to low levels of vitamin B12 because the vitamin is needed in order to support strong bones (4). Low bone mineral density can cause the bones to become increasingly fragile over time; women with low levels of vitamin B12 are considered to be at an increased risk of bone-related diseases and are more likely to experience overall poor bone health as they age.  


Red Blood Cell Formation and Production

One of the most important functions of vitamin B12 is the production of red blood cells in the body. When the body does not have adequate levels of vitamin B12, fewer blood cells are produced, and the red blood cells that are produced are abnormally shaped. Red blood cells are normally small and circular in shape, but red blood cells produced in a person with a deficiency of vitamin B12 will have larger, oval-shaped red blood cells. When shaped abnormally and larger in size, the red blood cells are unable to move from the bone marrow into the bloodstream quickly enough, which can result in a condition called megaloblastic anemia.


Supports Eye Health

Insufficient levels of vitamin B12 can contribute to poor eye health and increased likelihood of the onset of age-related eye disease. Vitamin B12 helps to lower homocysteine levels, an amino acid that is associated with a higher risk of age-related eye diseases when levels in the body are elevated.  


Supports Healthy Pregnancy

A vitamin B12 deficiency can cause significant birth defects, so it is especially important that pregnant women consume and absorb enough vitamin B12 to support both the mother and the baby. Vitamin B12 helps the baby's brain and nervous system to develop properly, and birth defects  can occur when not enough vitamin B12 is received during the early stages of pregnancy. Vitamin B12 deficiency is also associated with an increased risk of miscarriage or premature delivery (5)


Supports Energy Levels

Low energy levels, including feelings of fatigue and weakness, are common in people who are experiencing a vitamin B12 deficiency. One of the key enzymatic reactions B12 supports involves converting methylmalonic acid into a form of energy. Additionally, low energy levels and feelings of fatigue are the result of the low number of red blood cells in the body, which are responsible for delivering oxygen to the organs, tissues, and muscles. 

Without an adequate supply of oxygen, people can feel tired and have to work harder to accomplish even the simplest tasks. Although taking extra B12 won’t increase energy levels in people who already receive enough of the vitamin, one study showed that supplementing or increasing vitamin B12 intake can significantly improve energy levels for patients with a moderate to severe B12 deficiency (6).


Supports Mental Health and Mood

Vitamin B12 assists in the synthesis and metabolization of serotonin, one of the chemicals in the brain that is responsible for regulating our moods. Without an adequate supply of vitamin B12, we produce less serotonin, leading to changes in mood. People who do not consume and absorb sufficient amounts of vitamin B12 are twice as likely to experience severe mood changes compared to people who are not deficient (7). Adding a vitamin B12 supplement to prescription mental health medications as part of treatment has been found to result in greater relief from symptoms compared to prescription medications alone (7). 


What are the signs and symptoms of a vitamin B12 deficiency?

Many of the signs and symptoms of a vitamin B12 deficiency can be easily confused with other medical conditions, so diagnosis can be challenging. Additionally, symptoms may not appear for years if a patient has only a mild deficiency. Symptoms associated with a vitamin B12 deficiency include (8):

  • Fatigue and weakness due to a limited number of red blood cells available to transport oxygen throughout the body.
  • Glossitis, or inflamed tongue, and mouth ulcers that contribute to oral pain and irritation. Glossitis, accompanied by long, straight lesions on the tongue, is one of the most common early symptoms of vitamin B12 deficiency.  
  • Jaundiced or pale skin resulting from insufficient amounts of red blood cells.
  • Mobility changes, such as differences to walking or motion patterns, due to myelin deficiency, which causes damage to the nervous system. 
  • A feeling of pins and needles resulting from nerve damage that occurs as a result of a lack of properly produced myelin to protect and insulate the nerves.
  • Changes in mood and increased likelihood of depression and dementia, most likely due to high levels of homocysteine, which can interfere with the communication that occurs in the brain and damage brain tissue. 
  • Blurred or disturbed vision as a result of damage to the optic nerve in the eyes.
  • High temperature, although rare, can also be caused by a vitamin B12 deficiency.
  • Feeling out of breath or dizzy as a result of the body not getting enough oxygen from red blood cells.


Hopefully this has given you some insight as to how important vitamin B12 intake and absorption is for everyday health! If you think you may not be consuming enough B12 through diet alone, you may want to consider adding in oral supplements like GEM's whole food supplement, which provides not only vitamin B12, but a collection of essential nutrients like vitamin B6, magnesium, omega-3s, and many more that are in a form that is easily absorbed by your body!

Make sure to consult with your primary care physician or healthcare provider if you have concerns about a B12 deficiency, and also before adding any new supplement to your routine!


Fun Facts:
  • Unlike other vitamins, vitamin B12 can be stored in the body in large amounts for future use (up to 4000 micrograms!). An average person has enough vitamin B12 to last for three to five years (3).
  • Vitamin B12 deficiency is commonly misdiagnosed as folate deficiency; folate/folic acid is another B vitamin that assists in the formation of normal red blood cells.


By the Numbers:
  • 6: Average number of weeks it takes for anemia caused by B12 deficiency to resolve itself following supplementation (3).
  • 3 to 5: Number of years it can take for anemia to occur as a result of vitamin B12 deficiency due to the body’s B12 stores in the liver (3)

This article is based on scientific research and/or other scientific articles and contains trusted sources.

Our goal at GEM is to give readers up-to-date and objective information on health-related topics. GEM content is written by experienced health and lifestyle contributors and articles undergo an extensive review process.

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