Vitamin B12 deficiency: a well-known and thoroughly studied, yet under-diagnosed disease.

What is vitamin B12 and why is it important?

Vitamin B12 together with folate participates in DNA and red blood cells synthesis. It is also crucial for the nervous system since it is involved in the production of the myelin sheath around the nerves. Myelin performs the function of enabling efficient transmission of electrical signals in the brain. It contributes to mental clarity, concentration and memory function and the autoimmune response that destroys it results in a condition called Multiple Sclerosis or MS. Vitamin B12 is also known as the energy vitamin as it is involved in body energy production (ATP). It enables proper circulation, adrenal hormone production and supports the immune system and lots of other important fuctions.

Dietary sources of vitamin B12

Natural sources of vitamin B12 is meat like beef (specially the beef liver), chicken, pork (not processed pork products like bacon however), milk, eggs, venison, certain kinds of seafood, snapper, salmon, shrimp and scallops.

Unfortunately for vegetarians and vegans, vitamin B12 can only be found in animal tissues. The few plant foods that are sources of B12 are actually B12 analogues. An analogue is a substance that blocks the uptake of true B12, so your body’s need for the nutrient even increases.

Absorption of vitamin B12

The reason why absorbing vitamin B12 may be difficult for our system is because it is one of the largest molecules in the body. Actually, it is the largest known vitamin. Therefore, we require a binding protein called intrinsic factor. If your body isn’t producing intrinsic factor it’s impossible for the vitamin to get absorbed. To add to this the process is complex, requiring multiple successfully completed steps:

  1. Dietary vitamin B12 is normally bound to proteins in food of animal origin.
  2. As one consumes these foods pepsin and acid pH in the stomach will degrade these food proteins and release vitamin B12.
  3. The vitamin B12 that is now free then binds to the binding protein Intrinsic factor that enables it the transport through the small intestines. Without the intrinsic factor the pancreatic and intestinal enzymes would degrade B12 and render it useless for our bodies.
  4. In the mucosal cells of the distal ileum the vitamin B12-Intrinsic Factor complex is recognised by special receptors.
  5. Vitamin B12 is then released and enters the blood bound to another binding protein, transcobalamin, the complex is known as holotranscobalamin (Active B12). The majority of vitamin B12 (70-80%) in blood is bound to haptocorrin and only a minor proportion (20-30%) is bound to transcobalamin.
  6. Holotranscobalamin (Active B12) is the biologically active fraction of vitamin B12 in the blood as it is in only this form that vitamin B12 can be delivered into cells.

Vitamin B12 deficiency

Many factors play a role in for this process unravelling without disturbance. Several gastrointestinal conditions may cause problems, including: intestinal dysbiosis, leaky gut and/or gut inflammation, atrophic gastritis or hypochlorhydria (low stomach acid is strongly connected to low levels of intrinsic factor and this possible B12 deficiency). Pernicious anaemia (autoimmune condition), medications (especially PPIs and other acid-suppressing drugs, metformin, antibiotics, cholesterol-lowering drugs, antipsychotics, tuberculosis medications, drugs to treat Parkinson’s disease …), alcohol abuse, exposure to nitrous oxide (during surgery or recreational use), drinking too much coffee and age-related insufficient production of hydrochloric acid also increase the risk and may cause a B12 deficiency.

Above mentioned factors interfere with proper absorption but B12 deficiency can also be caused by a low intake through deficient diets, the most common being vegan and vegetarian diets.

Then again it is also possible to have adequate B12 levels and still have functional deficiency. This means that even your body has enough of the vitamin it doesn’t know how to use it properly. This could be because of genetic polymorphisms or just the intake of the wrong form. Most commercial supplements contain B12 (cobalamin) bound to cyanide, forming cyanocobalamin. The body has to methylate this form before being able to use it as meth-cobalamin. There are some good supplements on the market containing methyl-cobalamin directly so use those if you decide to supplement.

Symptoms of B12 deficiency

The last stage of vitamin B12 deficiency is anaemia. But being deficient may also cause:

  • weakness,
  • tiredness, or light-headedness,
  • heart palpitations and shortness of breath,
  • pale skin,
  • a smooth tongue,
  • constipation,
  • diarrhoea,
  • loss of appetite or gas,
  • nerve problems like numbness or tingling,
  • muscle weakness,
  • problems walking,
  • loss of vision,
  • mental problems like depression,
  • memory loss or behavioural changes,
  • sleep problems,
  • neurological and neuropsychiatric conditions,
  • cardiovascular and cerebrovascular diseases,
  • cancer
  • and others.

Pregnancy and vitamin B12

A baby whose mother is vitamin B12 deficient has a bigger chance of being born with neural tube defects, a class of birth defects affecting the infant’s brain and spinal cord. To add to this, these mothers are more likely to experience miscarriage.

Testing for B12 deficiency

I recommend you get your B12 and MMA serum levels lab tested, that way you get the most reliable results. A more pragmatic approach is to try eating more of before mentioned foods or start taking supplements and observe how your body reacts. If your symptoms vanish it is reasonable to suspect vitamin B12 deficiency was the cause.

Be sure your serum B12 is higher than 350 pg/mL. Even though this is in the middle of the usual reference range, studies have shown signs of deficiency below these levels.

A better marker of deficiency is a functional test marker known as Methyl Malonic Acid or MMA. It is a better marker because it is a metabolite the body produces when there is a functional B12 deficiency present. MMA is a reverse marker so to high levels indicate B12 shortage and that could be even at serum B12 in optimal ranges.

Why is vitamin B12 deficiency under-diagnosed?

As suggested from the Tufts University Framingham Offspring Study, vitamin B12 deficiency is a vastly spread occurrence. Their study shows 40 percent of people between the ages of 26 and 83 have plasma B12 levels in the low normal range – a range at which many experience neurological symptoms. 9 percent had outright deficiency, and 16 percent exhibited “near deficiency”.

There are two main reasons why most people remain untreated:

  • Doctors do not regularly check vitamin B12 levels.
  • The low end of the laboratory reference range is too low. Plenty people who experience symptoms due to vitamin B12 deficiency have “normal” levels of B12 (between 200 pg/mL and 350 pg/mL)

Treatment of B12 deficiency

After being diagnosed as vitamin B12 deficient you have multiple options depending on how severe your condition is. If you have pernicious anaemia, you’ll probably need regular Vitamin B12shots or high doses sublingual B12. If you have mild deficiency just changing your diet might be enough. Consuming vitamin B12 rich foods on a daily basis, a supplement or B12 injections usually solves the problem quickly. Older people experiencing a deficiency are advised to take a daily B12 supplement or a multivitamin that contains B12.

Being aware of the importance and role vitamin B12 has in our bodies is a crucial part in establishing a healthy diet and lifestyle which will prevent further complications and furthermore enable you to nurture yourself right.


B12 deficiency: a silent epidemic with serious consequences, Chris Kresser,

Vitamin B12: What to Know, WebMD,

Myelin: An Overview, Society for Neuroscience,

Vitamin B12 Absorption, Axis – shield,

Warning: Potentially Life Threatening Vitamin Deficiency Affects 25% of Adults, Dr. Mercola.

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