After finding out more about zinc and then learning all about iron in the last couple of blog posts, we’re now moving on to examine the third and final vitamin that requires stomach (hydrochloric) acid for absorption – Vitamin B12.

Why is Vitamin B12 so Important?

Vitamin B12 is the largest and the most complex of all vitamins and is the only known metabolite to contain cobalt. Vitamin B12 is an essential vitamin responsible for energy production, DNA synthesis and red blood cell production. It’s also crucial for our health due to its role in the nervous system where it contributes to the production of myelin – the outer layer of the nerve cells. As opposed to fat soluble vitamins such as vitamin A, D, E, K – which can potentially be toxic if taken in excess – vitamin B12 is water soluble which means it can be easily eliminated from our body. It is generally safe, even in high quantities, as larger intakes of vitamin B12 from food or supplements have not been shown to cause toxicity in healthy people.

Vitamin B12 Dietary Sources & Absorption

It is important to acknowledge that vitamin B12 is mostly bound to animal proteins and that food from plant sources contain no vitamin B12 whatsoever. Therefore, supplementation is necessary for vegans and, often, vegetarians too. Good sources of vitamin B12 include organ meats like liver or kidneys, eggs, fish, or dairy products – however, the intake of dairy products should be discussed with a healthcare professional in case of lactose intolerance or chronic health conditions. Intestinal bacteria can also produce some vitamin B12, but this is poorly absorbed. Nutritional yeast can be a good option for those who choose not to consume animal products. Interestingly, vitamin B12 is sensitive to light and oxygen but is less affected by heat, so processing practices involving higher temperatures that occur during cooking do not impair the integrity of the source.

Vitamin B12: The Three Phases of Absorption

Absorption of vitamin B12 is a highly complex process, which consists of 3 phases.

In the first phase, adequate levels of stomach acid are required for the release of the vitamin B12 from the food matrix.

In the second, active absorption of the vitamin takes place in the small intestine and it requires the so-called intrinsic factor (IF), which is a substance secreted by the stomach cells.

And in the third and final phase, the vitamin B12 – IF complex is absorbed and then transported to the cells in our body.

Things that Affect the Absorption of Vitamin B12

In certain circumstances such as gastritis (inflammation in the stomach), low stomach acid and increased alcohol intake, the production of IF can be affected.

Diseases affecting the bowel such as inflammatory bowel disease can also result in decreased absorption of this vitamin. Another condition which may lead to poor vitamin B12 absorption is pernicious anaemia, which is an autoimmune disease where the body produces antibodies that attack the stomach cells resulting in a lack of IF. In this case, addressing the autoimmune process and lifelong supplementation with vitamin B12 is necessary.

Absorption can also be impaired by other micronutrients such as vitamin B6 deficiency or excessive alcohol intake – as alcohol will decrease the absorption while increasing elimination of this vital vitamin.

It is also important to note that many medications can affect the absorption of Vitamin B12, including metformin (a drug frequently prescribed to people with diabetes), oral contraceptives, anti-gout medications, medications prescribed for reflux (as these alter the stomach pH), and medications prescribed for epilepsy (as they change the vitamin’s metabolism in the cerebrospinal fluid and can cause neuropsychiatric symptoms).

Vitamin B12 Deficiency: Signs & Symptoms

Vitamin B12 deficiency is quite common in elderly people. Those on long term medications are also at particular risk.

Signs of vitamin B12 deficiency include neurological symptoms such as tingling or numbness, impaired cognition and low mood and energy production, and even hormonal imbalances.

Conditions such as dementia and depression have also been linked to low vitamin B12 levels.

As low vitamin B12 levels can lead to higher rate of DNA damage, it has also been suggested that a healthy level of vitamin B12 in the body could play a role in the prevention of cancer.

Vitamin B12 deficiency, together with low levels of vitamin B6 and folic acid can also lead to hyperhomocysteinemia (high levels of homocysteine), which is a risk factor for vascular disease (such as heart disease) and could cause birth defects and recurrent pregnancy loss.

Because vitamin B12 plays a role in the formation of red blood cells, its deficiency can result in anaemia. But we also know that anaemia can also be a consequence of an iron deficiency – for information on the symptoms and treatment of iron deficiencies, please refer to the previous post.

Testing for Vitamin B12 Deficiencies

Vitamin B12 levels can be tested in the serum (blood), however this may not be a good enough indicator of what is really happening inside the cell. That’s why it’s recommended to also consider homocysteine and methylmalonic acid (MMA) levels, which would be elevated in case of B12 deficiency, in order to gain a better picture of the vitamin B12 status of the individual. Certain genetic polymorphisms including MTR/MTRR, TCN, FUT2 genes affect the metabolism.

During testing, it’s also important to understand that folate deficiency can present in the same way on blood test as low vitamin B12 levels – with low haemoglobin and increased MCV (mean cell volume), which means that the red cells are bigger than normal. And so, folate levels should be tested at the same time.

If folate alone is supplemented then the anaemia may resolve on the blood test. But, if the vitamin B12 deficiency is not addressed, the person will remain at an increased risk of neurological problems.

Treating the Deficiency

Vitamin B12 can be supplemented as an oral tablet, sublingually (which just means placing under the tongue to dissolve) or in the form of intramuscular injections. As the absorption of vitamin B12 is a very complex process, sublingual delivery or administration via an injection are more effective ways of supplementation. It should be noted that there are different forms of cobalamin (vitamin B12) such as hydroxocobalamin, methylcobalamin and adenocobalamin which are naturally occurring forms and cyanocobalamin, which is a synthetic form. In addition to concerns that the cyanocobalamin may release small amounts of cyanide, it is also an inactive form of vitamin B12 which means that the body cannot readily use it. Hydroxocobalamin is the form found in food and it is also inactive. On the other hand, methylcobalamin and adenocobalamin are both active forms which are preferable as supplements and are better at replenishing the body’s need for B12. Of these two, adenocobalamin is the most suitable for people with fatigue – while the methyl form crosses the blood brain barrier and protects the brain, and so is the most suitable for those with genetic polymorphisms (such as MTR/MTRR genes).

Vitamin B12 deficiency is quite common, and vegans are at particular risk because as mentioned earlier, plant-based foods do not contain it.

Interestingly, poor absorption of B12 is a more common cause of deficiency than a lack of the vitamin within the body due to insufficient dietary intake. When taking certain medication long-term such as metformin or the contraceptive pill, supplementation with vitamin B12 should be considered. It’s advisable, as well, to pay attention to the form of vitamin B12 supplements being taken contain to ensure that they are right for the individual’s situation and that the deficiency is addressed without compromising health in other areas.

Written by Dr Klaudia Raczko

If you’d like to enhance your body’s absorption of different microelements and learn about the intravenous infusion of vitamins, minerals, electrolytes, amino acids and other essential nutrients please call 0208 977 0679 or book an appointment with Dr Klaudia Raczko online.


Spence JD. Metabolic vitamin B12 deficiency: a missed opportunity to prevent dementia and stroke. Nutr Res. 2015; 36(2), pp 109-116

Weir DG, Scott JM. Vitamin B12 “Cobalamin.” In: Shils M, ed. Nutrition in Health and Disease. 9th ed. Baltimore: Williams & Wilkins; 1999: pp 447-458.