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6 signs of Vitamin B12 deficiency

In short

Vitamin B12 is a nutrient that is not produced by the body. It is obtained from our food (mainly animal products) or by taking supplements.

A vitamin B12 deficiency can manifest itself by various symptoms: fatigue, shortness of breath, feeling weak, muscle cramps, etc.

In order not to be deficient, it is important to maintain a good intake of vitamin B12, especially for vegetarians and vegans.

Vitamin B12 is one of the essential vitamins and minerals, which are not synthesized by the body and must therefore be provided entirely by the diet.
It plays several roles: it contributes in particular to maintaining a satisfactory level of energy in the body, to regulating the formation of red blood cells in the blood and to promoting effective immune defenses.  


Vitamin B12 is mainly found in meat and offal, certain types of shellfish and fish, and some cheeses. Therefore, vitamin B12 supplements are particularly recommended for vegans, as the majority of natural sources of B12 are of animal origin.  


Vegan or not, how do you know if you are vitamin B12 deficient? Here are 6 symptoms of a potential B12 deficiency.

1) Fatigue, shortness of breath: anaemia due to lack of vitamin B12

This is the best known and most likely symptom of vitamin B12 deficiency. Vitamin B12 helps to ensure a normal level of red blood cells in the blood. If there is a lack of B12, the red blood cells can become insufficient in number, which is called anaemia. This leads to a loss of energy, chronic fatigue and an overall feeling of weakness. Anemia can even lead to dizziness, and requires supplementation (with vitamin B12 and/or iron, for example) to resolve quickly.

2) Muscle cramps

Among its many actions, vitamin B12 is also involved in the functioning of the nervous system. If you are often subject to cramps, particularly during sleep, you may be lacking in B12.  


Cramp is a sudden, involuntary contraction of a muscle, which occurs because the muscle or nerves are too excitable. If the nerves are involved, your nervous system may not be functioning completely normally: vitamin B12 supplementation can then help to rectify the situation.

3) Loss of appetite and mouth ulcers

Lack of vitamin B12 can lead to loss of appetite, but also to mouth ulcers and other visible symptoms in your mouth. A swollen, red and/or painful tongue, or atrophied papillae can alert you to a B12 deficiency. 

vitamin B12 deficiency

4) Brain and memory problems

Vitamin B12 has direct influences on psychology and cognitive abilities. Too little B12 can lead to memory loss and, in the most serious cases, to Alzheimer's-like symptoms or dementia, such as hallucinations. Vitamin B12 supplementation is also indicated for the elderly to partially compensate for this.

5) Irritability due to vitamin B12 deficiency

Another possible mental consequence of a B12 deficiency is irritability and bad temper. Some people with B12 deficiency become irritable too easily, unusually irascible, even confused or depressed.

6) Constipation and stomach problems

Finally, vitamin B12 deficiency can lead to various symptoms and digestive disorders: vomiting, nausea, constipation, flatulence and even abdominal pain.

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