Family doctor



Vitamin B 12


Outline of causes of deficiency and treatment of this essential vitamin.


Vitamin B12 (also known as cobalamin) is an essential vitamin required for the healthy functioning of nerves, blood cells and DNA synthesis. It is the largest and most complex of all the vitamins.

 Because humans and plants are incapable of producing vitamin B12, we are reliant on animal-based food products as our main source.

 This includes fish, shellfish, meat, milk products and eggs. Edible algae are the only plant foods that naturally contain significant amounts of vitamin B12.

 Vegans and to a lesser extent, vegetarians are at a much higher risk of deficiency than meat-eaters. Vegans must make a deliberate effort to incorporate vitamin B12 rich foods into their diet such as algae, B12 fortified cereals or supplements.

 The elderly are also at a higher risk of B12 deficiency because the body’s ability to absorb B12 reduces as we age.

 The body can store several years’ worth of B12 in the liver so low levels in the blood stream are rare in younger, healthy, non-vegans.

Symptoms of a deficiency may take 2 years to develop because of the reserve from these stores.

 Causes of vitamin B12 deficiency

 B12 deficiency can occur with:

  • Reduced dietary intake (e.g in vegans)

  • Absorption problems


The absorption of vitamin B12 is a complex process that relies on a number of different bodily functions.


The first step in absorption occurs in the stomach where acid is required to release protein-bound B12.

 Conditions that reduce stomach acid such as chronic stomach inflammation (atrophic gastritis, common in the elderly) and long-term use of stomach acid lowering medications such as omeprazole may impair this process.

 A condition called pernicious anaemia is an autoimmune disease that prevents the stomach from properly processing B12 and invariably leads to vitamin B12 deficiency (see article on Pernicious Anaemia).


Next, functioning enzymes from the pancreas are required to further extract B12 from food. People with chronic pancreatitis may have reduced B12 absorption because of this.

 Finally, a functioning small bowel (the ileum) is required to absorb B12 into the blood stream.


Bowel problems such as Crohn’s disease, ileitis or coeliac disease may impair this absorption. Bowel or stomach resection for certain cancers or weight loss surgery may also result in reduced absorption.


B12 deficiency is common in people with alcoholism because of poor nutrition and the body’s decreased ability to release protein-bound B12.


Summary of the causes of B12 deficiency:


  • Reduced intake (vegans, some vegetarians)

  • Stomach acid reduction such as long term use of omeprazole

  • Atrophic gastritis (chronic inflammation of the stomach lining) particularly in the elderly

  • Pernicious anaemia

  • Chronic pancreatitis

  • Bowel inflammation such as Crohn’s, ileitis and coeliac disease

  • Bowel or stomach resection

  • Alcoholism


Signs and symptoms of B12 deficiency


Vitamin B12 deficiency can lead to anaemia and neuropathy (nerve damage). This is because B12 is crucial in the formation of red blood cells and nerve health.


  • Symptoms of anaemia

    • Fatigue and weakness

    • Dizziness

    • Shortness of breath

    • Rapid heart beat

    • Paleness

  • Symptoms of nerve dysfunction

    • Mild depression and confusion

    • Memory loss

    • Hallucinations, personality and mood changes

    • Numbness and tingling in the feet and hands

    • Unsteady walking and loss of position sense

    • Damage to the optic nerve (responsible for eyesight)

  • General consequences of B12 deficiency

    • Sore red tongue

    • Mouth ulcers

  • Symptoms of inadequate absorption

    • Weight loss


If you suspect that you are at an increased risk of B12 deficiency, or are experiencing symptoms, let your family doctor know who can do a simple blood test to quantify this.


Vitamin B12 food sources


The recommended daily intake of B12 is 2.4 mcg/day for non-pregnant adults.

Because the body has the ability to store B12 for long periods of time, the specific details of daily intake are not hugely important. Most people who eat meat and dairy products regularly will have no trouble at all maintaining adequate levels of B12. Food with high levels of B12 include:


  • Fish – particularly high content in salmon, herring, tuna, and fish soup stocks

  • Shellfish – particularly oysters, muscles and clams

  • Meat - particularly organ meat such as liver and kidney, and beef

  • Cow’s Milk and cheese, cottage cheese, hard cheese, blue cheese, yoghurt

  • Eggs (most of the B12 is found in the egg yolk)

  • Edible Algae- nori, dried green and purple algae

  • Vitamin B12 fortified cereals


Some soy products are also fortified with B12, check the nutritional facts on the back of the packet to see if they are.




The treatment of B12 deficiency depends on the underlying cause.


If the deficiency is due to inadequate intake, this can be remedied through supplementation or increased intake of foods naturally high in B12.


In other cases, the underlying cause of the deficiency should be treated and B12 supplemented until the body is able to replenish its own stores. In some cases, the cause of B12 deficiency may be irreversible and life-long B12 supplementation may be required.


The most common form of B12 replacement is via an intramuscular injection because the body doesn’t readily absorb oral B12 supplements.


However, in milder forms of deficiency (commonly those due to reduced intake) replacement with a high dose oral form of B12 may be just as effective as an injection.


Oral supplementation is less effective at treating a deficiency caused by the reduced absorption of B12. Bypassing the stomach and intestines through an intramuscular injection is the most efficient way of delivering B12 into the bloodstream in these cases.


Your family doctor will be able to tell you about which form of B12 supplementation is suitable for you.



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