B12 – the forgotten B vitamin?

DietDoc highlights the importance of vitamin B12, its uptake and functions, the causes of B12 deficiency, and what can be done to treat such deficiencies.

With the spotlight always on something sensational like government interventions or the latest fad diet, we sometimes forget about basic nutrients such as vitamin B12.

An excellent summary of B12 was published by Dr Barry Shmeizer in this month’s Medical Chronicle. Dr Shmeizer discusses uptake and functions, the causes of B12 deficiency, and what can be done to treat such deficiencies – something readers may also find useful.

Requirements for the absorption of B12

Many nutrients have a simple absorption system based on differences between the concentration of the given nutrient in the gut and the concentration of the same nutrient in the liquid (blood or lymph) which moves the nutrient to body’s cells. The absorption of vitamin B12 is, however, considerably more complicated.

According to Dr Shmeizer (2015), vitamin B12 which is found exclusively in food derived from animals (meat, seafood and dairy products), must be released from the protein food it is found in by the acid in the stomach. Vitamin B12 then binds to so-called R factors (proteins) in the gastric juices and has to be released in the duodenum from these proteins by the enzyme pepsin which is produced by the pancreas. Vitamin B12 subsequently binds to a compound called the intrinsic factor (IF) and this combination of vitamin and IF has to bind with a specific receptor (cubulin) in the ileum of the gut to be absorbed into the circulation.

It stands to reason that the following factors must all be in place to ensure that we obtain adequate supplies of vitamin B12:

– An adequate intake from foods such as meat, fish and dairy or if your diet is deficient in vitamin B12, then from supplements containing vitamin B12 (see below for the relative inefficiency of oral supplements)

– Sufficient gastric acid to release B12 from protein food. Elderly people often have a deficiency of stomach acid and may suffer from a chronic vitamin B12 deficiency.

– Protease enzymes produced by the pancreas to separate B12 from the R factors so that it can bind to IF – the intrinsic factor

– Adequate quantities of IF to ensure that B12 can bind with the cubulin receptor that transports the vitamin into the blood

If any one of these above mentioned factors is absent for a longer period of time, the individual in question may develop a vitamin B12 deficiency, leading to pernicious or megaloblastic anaemia and neurological degeneration.

Why do we need Vitamin B12?

Vitamin B12 (also called cobalamin) acts as a co-factor (a helper) in the synthesis of DNA in body cells that divide rapidly, such as the cells producing red blood cells and enterocytes (cells that line the digestive tract).

During DNA synthesis, a compound called methionine is formed which leads to decreased homocysteine levels. If we have a methionine deficiency, it can cause degeneration of the nerves (neuropathy) and brain. Raised homocysteine levels have been implicated in heart disease. Vitamin B12, is therefore, essential for normal DNA synthesis, normal blood production and nerve function.

Vitamin B12 deficiency

For most people who have an adequate intake of vitamin B12 from food derived from animals such as meat, liver, fish, milk and dairy products, a vitamin B12 deficiency is not really a problem unless they develop an autoimmune disease that leads to pernicious anaemia.

Originally pernicious anaemia, which is caused by an inability to produce IF or intrinsic factor for the absorption of vitamin B12, was regarded as a purely genetic disease, but currently it is suspected that this anaemia with its deficiency of IF which in turn leads to a deficiency of B12, is probably an autoimmune disease.

Dr Shmeizer mentions that pernicious anaemia can also be associated with other autoimmune diseases like thyroid disease, diabetes, vitiligo (a condition characterised by loss of pigment in the skin), and Addison’s disease (a condition that occurs when there is a loss of hormones produced by the adrenal cortex).

Other non-IF factors that can cause vitamin B12 deficiency and pernicious anaemia are:

– Patients who have had a gastrectomy (removal of part or all of the stomach), lack the stomach acid and pepsin enzyme required for the absorption of B12.

– Gastritis patients, particularly elderly person and patients with Helicobacter pylori infection which is linked to ulcers

– Malabsorption such as coeliac disease in patients who are allergic to gluten

– A condition known as “blind loop syndrome” where bacterial overgrowth in the gut is so great that it interferes with the absorption of B12 and other nutrients

– Diseases/damage of the ileal part of the gut such as Crohn’s disease, lymphoma, surgical resection, or deep X-ray therapy

– Bariatric surgery for slimming purposes which may remove those parts of the stomach or gut that are essential for B12 absorption

– Diseases of the pancreas which prevent production of the enzymes required for the absorption of B12

– Tapeworm acquired from eating raw fish (only eat Sushi at reputable restaurants!)

– Chronic alcoholism

– Certain medications – high doses of proton pump inhibitors to treat ulcers and gastritis and metformin (Glucophage), which is used to treat type 2 diabetes, may interfere with B12 uptake

– Hereditary tendency

– Inadequate dietary intake. Dr Shmeizer (2015) emphasises that strict vegans and vegetarians, pregnant and lactating women all need to ensure that their B12 intake is adequate to prevent pernicious anaemia.

Symptoms of Vitamin B12 Deficiency

In keeping with its role in DNA synthesis mentioned above, a deficiency of vitamin B12 can lead to the development of megaloblastic anaemia and neurological disturbances.

Anaemia patients have a sallow appearance, prematurely grey hair, lack of mental sharpness and a broad-based gait (walk with feet apart).

The neurological changes associated with a vitamin B12 deficiency include the following:

– Degeneration of the spinal cord, which particularly affects the legs more severely than the arms and is specific for B12 deficiency. Patients suffer from abnormal sensations in the hands and feet such as pins and needles, some loss of control of their movements, loss of position and the ability to sense vibrations. If the deficiency is severe the patient may become spastic, paraplegic and incontinent.

– Damage to the brain may manifest through subtle memory loss developing to full dementia, irritability and damage to sight because of the degeneration of the optic nerve.

The neurological fall-out caused by vitamin B12 deficiency is so severe that we all need to guard against having low intakes of this vitamin. The old habit of eating liver once a week was not a bad idea at all!

Sources of vitamin B12

The following foods are rich to adequate sources of B12 per 100g.

– Liver – 70.7 microgram (mcg)

– Clams – 98.9 mcg

– Tuna, canned in water – 3.00 mcg

– Beef, lean – 2.81 mcg

– Fish, baked – 2.56 mcg

– Milk, skim – 0,52 mg (but per 250 ml milk contains 1.30 mcg of B12)

– Yoghurt with fruit – 0,70 mcg

– Ready-to-eat- breakfast cereals – 1.8 to 2 mcg (per ½ cup or 50g, these cereals contribute 0,9 to 1 mcg)

(Note that in South Africa vitamin B12 is not part of the 8 nutrient mixture added to fortified wheat bread and maize meal).

In this country, the Nutrient Reference Value (NRV) for vitamin B12 is 2,4 mcg/day for persons of 4 years and older. The USA RDA varies from about 2,4 mcg/day for adult men and women to 2,6 mcg/day during pregnancy and 2,8 mcg/day for breastfeeding mothers.


a) Injections

If diagnosed with pernicious anaemia the doctor will probably treat you with injections of 1 mg of vitamin B12 per day for a week, followed by once a week for a month and then once a month for the rest of your life if the condition does not clear up. In patients where the cause can be eliminated, the injections can be stopped when body levels of vitamin B12 return to normal.

b) Oral supplements

Because absorption of B12 from tablets and capsules can be poor, Dr Shmeizer recommends the use of mega-dosses of 1-2 mg vitamin B12 a day and cautions that if possible injections should be used instead or oral supplements.

Vitamin B12 may be one of the forgotten vitamins, but it is important to keep in mind that we need a steady intake throughout our lives. Anyone who does not eat foods derived from animals, the senior population, and pregnant and lactating women, should check their intake and have tests done to determine if they suffer from vitamin B12 deficiency.


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