B12 deficiency: symptoms, causes and what to do about it

What is vitamin B12, and what is it used for?

Vitamin B12 (or cobalamin) is a water-soluble vitamin that is essential for the body to function properly. It is involved in many fundamental biological processes, which explains why a deficiency can have multiple repercussions.

Vitamin B12 contributes to normal energy metabolism and the normal metabolism of homocysteine (an amino acid produced naturally by the body during protein metabolism).

It also plays a key role in the proper functioning of the nervous system and contributes to normal psychological functions. It is also essential for the production of healthy, functional red blood cells.

With its action on energy production, tissue oxygenation and nerve function, vitamin B12 helps to reduce feelings of tiredness and exhaustion.

B12 also supports the body's natural defences, taking part in DNA synthesis (it contributes to the process of cell division) and the normal functioning of the immune system.

The special feature of vitamin B12 is that it is found almost exclusively in animal products: meat, offal, eggs, dairy products, fish and seafood, etc. This is why populations that eat little of this type of food are particularly exposed to the risk of deficiency.

What are the symptoms of vitamin B12 deficiency?

A vitamin B12 deficiency can cause a wide variety of symptoms, sometimes appearing several months (or even several years) after the onset of the deficiency. If in doubt, it is always advisable to consult a doctor.

Unexplained chronic fatigue

As B12 is involved in the formation of red blood cells, a deficiency can lead to so-called ‘megaloblastic’ anaemia, characterised by red blood cells that are too large and inefficient.

The result is poor oxygenation of tissues, manifested by persistent fatigue, even at rest (1).

Mood and nervous system disorders

Vitamin B12 is essential for the nervous system to function properly. In our bodies, it plays a role in the synthesis of myelin, the protective sheath of the nerves.

A deficiency can lead to:

• mood disorders (irritability, mild to moderate depression) (2);
• cognitive problems (memory problems, difficulty concentrating);
• tingling in the feet and hands, numbness and even loss of feeling in the extremities (peripheral neurological symptoms) (3).

Weight loss and digestive problems

Loss of appetite or unexplained weight loss can also be signs of severe deficiency, particularly when the deficiency is linked to an underlying digestive disorder.

In some cases, glossitis (inflammation of the tongue) (4), constipation and diarrhoea, or abdominal pain may also be observed.

A diagnosis to be confirmed by a blood test

When in doubt, the diagnosis can only be confirmed by a blood test.

The doctor generally prescribes a vitamin B12 blood test, sometimes supplemented by other markers (such as homocysteine or methylmalonic acid, for a more accurate assessment).

What are the common causes of B12 deficiency?

Vitamin B12 deficiency can be caused by a number of factors, including inadequate intake, poor absorption or increased needs. Hence the importance of early detection, particularly in people at risk.

An unbalanced or restrictive diet

People who follow a strict vegetarian or vegan diet without supplementation are particularly at risk, as B12 is not found in plants (5).

Very restrictive diets, undernutrition and certain eating disorders can also lead to deficiencies.

Digestive disorders and absorption pathologies

Vitamin B12 needs a specific environment to be absorbed from the intestine. In particular, it depends on the secretion of intrinsic factor (IF), a protein produced by the stomach. In its absence, B12 cannot be absorbed.

Biermer's disease (or pernicious anaemia) is an autoimmune disease that prevents this production. It is one of the main causes of vitamin B12 deficiency (6).

The production of transport proteins and the absorption capacity of vitamin B12 also decline with age.

Other conditions, such as gastric atrophy, coeliac disease, Crohn's disease and certain bariatric surgeries (bypass) can also interfere with its absorption (7).

Long-term medication and treatments

Some long-term treatments can reduce the absorption of vitamin B12, in particular:

• proton pump inhibitors (PPIs) and antacids (8)
• metformin (in type 2 diabetes) (9)
• certain antibiotics or anticonvulsants (anti-epileptics)

How can vitamin B12 deficiency be prevented or corrected?

Vitamin B12 deficiency can be effectively prevented or corrected with a suitable diet. In some cases, it is advisable to opt for targeted supplementation in the form of well-dosed, easily assimilated supplements.

Eat foods rich in B12

For omnivores, a varied and balanced diet is generally sufficient to cover the body's vitamin B12 requirements.

Foods rich in vitamin B12 (10) include:

• offal (liver, kidneys)
• red meat and poultry
• oily fish and seafood
• eggs and dairy products

However, in some cases, such as a vegan diet, malabsorption or chronic illness, these dietary intakes are not enough.

B12 supplementation: when is it necessary?

In high-risk situations (vegetarian or vegan diet, Biermer's disease, digestive surgery, the elderly, etc.), supplementation is strongly recommended (11).

Vitamin B12 is available in two main forms:

• Cyanocobalamin: effective and inexpensive, this is the most widely used synthetic form.
• Methylcobalamin: the most active form, directly usable by the body, it is particularly useful in cases of activation disorders or oxidative stress.

Vitamin B12 can be taken in the form of capsules, drops or tablets to be dissolved under the tongue.

• Discover the dietary supplement Methylcobalamin, formulated from pure, bioavailable methylcobalamin, for optimal assimilation on a daily basis.

In general, the doses used for prevention or maintenance vary from 500 µg to 1000 µg per day, well above the recommended daily intake (because digestive absorption of B12 is limited by saturation).