In short:
- Vitamin B12 contributes in particular to a reduction of tiredness and fatigue, to the normal functioning of the nervous system and to normal red blood cell formation, according to the EU register of claims.
- A deficiency most often comes from an insufficient dietary intake (a vegan diet), digestive malabsorption or certain long-term treatments.
- Tiredness, paleness and breathlessness are the most common signs; neurological problems (tingling, memory issues) can also appear.
- Only a blood test confirms a deficiency: if in doubt, ask a doctor.
A vitamin B12 deficiency sets in when the body no longer has enough of this vitamin, which is essential for the nervous system and for making red blood cells. It mostly affects certain identified profiles: older people, vegans, people on certain treatments. This fact sheet sets out the causes, the symptoms and what to do.
Vitamin B12 deficiency at a glance
| Benchmark | Value or information |
|---|---|
| Authorised roles | Reduction of tiredness and fatigue, normal functioning of the nervous system, normal red blood cell formation |
| Label reference value | 2.5 µg a day (NRV) |
| Adult satisfactory intake (ANSES) | 4 µg a day |
| Dietary sources | Almost exclusively animal products: meat, fish, eggs, dairy |
| Profiles most at risk | Vegans, older people, chronic digestive disease, long-term treatments (metformin, acid-reducers) |
| Diagnosis | Blood test (vitamin B12 level), made by a doctor |
What is vitamin B12?
Vitamin B12, or cobalamin, is a water-soluble vitamin that the body cannot make and must obtain from food. It is involved in making red blood cells, in homocysteine metabolism and in the functioning of the nervous system.
The EU register of claims1 recognises several authorised claims for vitamin B12. Vitamin B12 contributes:
- to a reduction of tiredness and fatigue;
- to normal energy-yielding metabolism;
- to the normal functioning of the nervous system;
- to normal psychological function;
- to normal red blood cell formation;
- to normal homocysteine metabolism;
- to the normal function of the immune system;
- and it has a role in the process of cell division.
Vitamin B12 is found almost exclusively in animal products. This is the main reason vegan diets carry a risk of deficiency, unless supplemented or combined with fortified foods.
The causes of a vitamin B12 deficiency
A vitamin B12 deficiency usually has one of these three origins.
| Cause | What to know |
|---|---|
| Insufficient dietary intake | A vegan or strict vegetarian diet, without fortified foods or a supplement: vitamin B12 is almost absent from plant foods |
| Digestive malabsorption | Autoimmune gastritis (pernicious anaemia), Crohn’s disease, coeliac disease, stomach or duodenum surgery, pancreatic insufficiency |
| Long-term medication | Metformin (type 2 diabetes), proton pump inhibitors and other acid-reducers, which reduce the absorption of the vitamin |
On top of this, stomach acidity naturally decreases with age, which reduces the release of vitamin B12 from food: this is one reason older people are more at risk.
Who is most at risk of a vitamin B12 shortfall?
The US NIH fact sheet on vitamin B122 lists several profiles more exposed to an insufficient intake or to malabsorption.
| Profile | Why |
|---|---|
| Vegans and strict vegetarians | Vitamin B12 is almost absent from plant-based foods |
| Older people | Lower stomach acidity, which reduces the release of the vitamin from food |
| Chronic digestive diseases | Reduced intestinal absorption (Crohn’s disease, coeliac disease, autoimmune gastritis) |
| People who have had stomach surgery | Bariatric or gastric surgery reduces the absorption area |
| Long-term metformin or acid-reducer treatment | These medications can reduce the absorption of vitamin B12 |
| Pregnant or breastfeeding women | Needs increase compared with the usual satisfactory intake |
The symptoms of a vitamin B12 deficiency
The most common signs
A vitamin B12 deficiency often sets in gradually. The first signs are not very specific: intense tiredness, paleness linked to anaemia, breathlessness on exertion, loss of appetite and an inflamed tongue. These signs have many other possible causes: only a blood test, interpreted by a doctor, can link them to a vitamin B12 deficiency.
Neurological symptoms
According to the same source2, neurological symptoms can appear, sometimes even before anaemia is detected, particularly in older people: tingling or numbness in the hands and feet, balance or walking problems, memory problems, confusion or irritability. Left untreated, these problems can become long-lasting, which is why a prompt medical opinion is recommended when these signs appear.
How do you know if you are short on vitamin B12?
Only a blood test can measure vitamin B12 levels and confirm a deficiency. A doctor may supplement this with other markers (homocysteine, methylmalonic acid) when the result is borderline3. It is also the doctor who looks for the cause (dietary, digestive, medication-related) and decides on the appropriate treatment: diet, an oral supplement or, for some causes of malabsorption, an injectable form.
How to prevent or correct a vitamin B12 deficiency
Vitamin B12 is found almost exclusively in animal-derived foods.
| Food | Why it matters |
|---|---|
| Offal (liver) | Among the most concentrated sources of vitamin B12 |
| Fish and seafood (mackerel, sardines, oysters) | A good source of vitamin B12 |
| Meat | Beef, poultry: a regular source depending on consumption |
| Eggs | A source of vitamin B12, more modest than meat or fish |
| Dairy products | Milk, yoghurt, cheese: contribute to daily intake |
| Fortified foods | Some cereals or plant-based drinks fortified with vitamin B12, useful when animal products are absent |
For someone on a vegan diet, no plant source reliably covers needs: fortified foods or a vitamin B12 supplement are then recommended. The guide on micronutrition and diet explains how to spot the most common deficiencies depending on the diet followed, and the page on vitamin and mineral needs places vitamin B12 among the other micronutrients.
Beyond diet, an existing deficiency is corrected under medical supervision: it is the doctor who chooses the form (oral or injectable) and the length of treatment based on the cause found. The page on vitamin courses for tiredness and the one on winter vitamins cover other vitamins worth watching depending on the season.
Key takeaways
- Vitamin B12 contributes in particular to a reduction of tiredness and fatigue, to the normal functioning of the nervous system and to normal red blood cell formation.
- A deficiency most often comes from an insufficient dietary intake, digestive malabsorption or certain long-term treatments.
- Vegans, older people and people with a chronic digestive disease are the profiles most at risk.
- Only a blood test confirms a deficiency: suggestive symptoms, particularly neurological ones, call for a prompt medical opinion.
Frequently asked questions
What causes a vitamin B12 deficiency?
The three most common causes are an insufficient dietary intake (a vegan or strict vegetarian diet without supplementation), digestive malabsorption (autoimmune gastritis, Crohn’s disease, coeliac disease, stomach surgery) and certain long-term treatments such as metformin or proton pump inhibitors, which reduce the absorption of the vitamin.
What are the symptoms of a vitamin B12 deficiency?
The most common signs are intense tiredness, paleness linked to anaemia, breathlessness on exertion and loss of appetite. Neurological symptoms can also appear: tingling in the hands and feet, balance problems, memory problems or irritability.
Who is most at risk of a vitamin B12 shortfall?
People following a vegan or strict vegetarian diet, older people, those with a chronic digestive disease, people on long-term metformin or acid-reducing treatment, and pregnant or breastfeeding women, whose needs increase.
How do you know if you are short on vitamin B12?
Only a blood test can measure vitamin B12 levels and confirm a deficiency. If you have suggestive symptoms or a risk factor, the diagnosis and treatment decision are for a doctor to make.
Does vitamin B12 have an immediate effect once a deficiency is corrected?
No, no claim refers to an immediate effect. Vitamin B12 contributes to a reduction of tiredness and fatigue and to the normal functioning of the nervous system, but correcting a deficiency and monitoring symptoms are for the doctor who made the diagnosis.