Vitamin B12: Cobalamin – Key Benefits, Sources and Essential Supplements.

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Discover why vitamin B12, also known as cobalamin, is essential for your health and how to avoid silent deficiencies. This complete guide reveals its key roles in energy production, proper brain and nervous system function, as well as the formation of red blood cells. You’ll learn what the best food sources are, who is most at risk of lacking B12, and how to detect it effectively. We’ll also cover the different forms of supplements and their specificities. Whether you are omnivore, vegetarian, or vegan, this article will help you make the right choices. Don’t let a deficiency compromise your vitality — read now to understand everything about this indispensable vitamin.

TABLE OF CONTENTS

WHAT IS VITAMIN B12?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin essential for the proper functioning of the body. It belongs to the B vitamin group and is distinguished by its complex chemical structure centered around a cobalt atom, hence its name.

Unlike other vitamins, B12 is not produced by plants or animals themselves, but by certain bacteria mainly found in the soil or in the digestive tract of some animals.

A VITAMIN WITH MULTIPLE ROLES

Cobalamin plays a vital role in several key biological functions:

• It contributes to the formation of red blood cells by participating in DNA production within the bone marrow. An insufficient intake can therefore lead to so-called “megaloblastic” anemia.

• It is essential for the proper functioning of the nervous system, particularly by contributing to the synthesis of myelin, the protective sheath surrounding the nerves. A deficiency can cause severe neurological disorders, sometimes irreversible.

• It is involved in the metabolism of fatty acids and amino acids, allowing energy to be released from consumed nutrients.

• It helps regulate homocysteine levels in the blood, an amino acid whose excess is associated with an increased cardiovascular risk.

A VITAMIN OF EXCLUSIVELY ANIMAL ORIGIN

The human body is unable to produce vitamin B12, which makes a dietary or supplemental intake essential.

It is naturally present only in animal-based foods (meat, fish, eggs, dairy products), as these contain bacteria capable of synthesizing it in their digestive systems.

A VITAMIN STORED, BUT NOT ALWAYS ABSORBED

The human liver is capable of storing large amounts of vitamin B12, which explains why a deficiency can take several months, or even years, to manifest.

However, some people have a reduced absorption of the vitamin, particularly due to digestive disorders, age, or the prolonged use of certain medications, which sometimes makes supplementation necessary.

IN SUMMARY

Vitamin B12 is an essential molecule for cellular life, nervous system health, and blood production.

Awareness and monitoring of it are all the more important among people following a vegan diet or suffering from digestive disorders affecting absorption.

WHAT ARE THE BENEFITS OF VITAMIN B12?

Vitamin B12 performs essential functions for maintaining overall health

Present in very small amounts in the body but of vital importance, it acts at several physiological levels, both cellular, nervous, and immune. A deficiency can lead to a series of sometimes serious disorders, highlighting the importance of a sufficient and regular intake.

Red blood cell formation and anemia prevention

One of the best-known roles of vitamin B12 is its contribution to the production of red blood cells. It is involved in the synthesis of DNA, an essential process for cell division in the bone marrow. In case of deficiency, this production is disrupted, leading to so-called megaloblastic anemia, characterized by red blood cells that are too large and ineffective at transporting oxygen. This form of anemia often results in great fatigue, shortness of breath, and paleness.

Support of the nervous system and protection of myelin

Vitamin B12 is also involved in the synthesis of myelin, a fatty substance that surrounds nerve fibers and ensures the rapid and efficient transmission of nerve signals. A deficiency in B12 can cause neurological disorders such as tingling, numbness, loss of balance, or even cognitive disorders or symptoms similar to depression. These effects can be irreversible if the deficiency persists too long.

Energy production and metabolism

B12 plays a crucial role in the metabolism of fatty acids and amino acids, allowing the body to extract energy from nutrients. It is a key cofactor in the Krebs cycle (the energy cycle of cells), making cobalamin an indispensable ally against chronic fatigue and energy slumps. It notably allows the conversion of homocysteine into methionine, an amino acid important for cellular and liver health.

Maintenance of cognitive functions

Vitamin B12 contributes to the proper functioning of the brain, particularly by supporting neurotransmitters responsible for memory, concentration, and mood. Several studies link low B12 levels to cognitive disorders, especially in older adults. It also plays a role in preventing age-related cognitive decline, although the data remains partially controversial.

Reduction of fatigue and immune support

A deficiency in B12 often manifests as persistent fatigue, even in the absence of diagnosed anemia. By restoring normal levels of red blood cells and facilitating energy production, vitamin B12 helps restore vitality and endurance. It also contributes to the proper functioning of the immune system, although its action is not direct: it promotes overall balance, enabling the body to better resist external aggressions.

WHICH FOODS ARE RICH IN VITAMIN B12?

Vitamin B12 is exclusively synthesized by microorganisms (bacteria) and is only naturally found in animal-based products. This means that diet plays a crucial role in cobalamin intake, especially for people following restrictive diets such as vegetarianism or veganism. Knowing the richest food sources helps effectively prevent deficiencies.

Organ meats: the champions of vitamin B12

Animal livers are the most concentrated foods in vitamin B12. Beef liver, for example, contains up to 70 to 100 µg of B12 per 100 g, which is more than 20 times the recommended daily intake. Kidneys are also excellent sources. Although less commonly consumed in modern diets, their richness in micronutrients makes them highly effective foods for quickly replenishing stores.

Fish: a valuable marine source

Many fatty and lean fish are rich in vitamin B12. Among the most concentrated are:

Mackerel
Sardine
Salmon
Tuna
Herring

These fish provide not only vitamin B12, but also omega-3 fatty acids, which are beneficial for the heart and brain. A 100 g serving of sardines can easily cover daily B12 needs.

Shellfish: small but powerful

Clams, mussels, oysters, and scallops are among the richest B12 foods in the animal kingdom. For example, 100 g of clams can contain more than 80 µg of B12. These shellfish are also excellent sources of iron, zinc, and protein, making them particularly valuable nutritionally.

Meats: regular and accessible sources

Meat, especially beef, pork, lamb, or poultry, provides moderate but sufficient amounts of vitamin B12 when consumed regularly. Muscle meat contains less B12 than organ meats, but it remains a reliable source for a balanced diet. A 100 g serving of red meat can contain between 1 and 5 µg of cobalamin.

Dairy products and eggs: an option for vegetarians

Milk, cheeses (particularly hard cheeses like Emmental or Comté), and eggs are the main sources of vitamin B12 for people who do not eat meat or fish. However, their content is lower: one egg provides about 0.9 µg of B12, and 100 ml of milk contains about 0.5 µg. These foods can contribute to daily intake but are rarely sufficient to meet needs in cases of strict dietary restriction.

Note

Plant foods do not naturally contain active B12. Some algae such as spirulina or nori are sometimes cited as sources, but they contain inactive analogues, unusable by the human body. This is why vegan diets require mandatory vitamin B12 supplementation or regular consumption of fortified foods.

WHO IS AT RISK OF A VITAMIN B12 DEFICIENCY?

Although the body can store vitamin B12 for several years, some people are at increased risk of deficiency. This situation can result from an insufficient dietary intake, poor intestinal absorption, or a combination of both. Identifying the most at-risk groups makes it possible to implement appropriate preventive measures, particularly through supplementation or medical monitoring.

People following a vegetarian or vegan diet

Since animal products are the only natural sources of vitamin B12, people who exclude meat, fish, eggs, and dairy products from their diet are directly exposed to insufficiency. While vegetarians may sometimes meet their needs through eggs and dairy, vegans must rely on fortified foods or supplements to avoid medium-term deficiencies.

Older adults

With age, the body’s ability to absorb vitamin B12 naturally decreases. This phenomenon is often linked to a reduction in hydrochloric acid secretion in the stomach, which is essential for releasing B12 from food. Older adults may therefore develop a deficiency without changing their diet, which justifies regular screening in people over 60, even in the absence of obvious symptoms.

Pregnant or breastfeeding women

During pregnancy and breastfeeding, the need for vitamin B12 increases. An uncorrected deficiency in the mother can have effects on the neurological development of the fetus or infant. This risk is particularly high in pregnant women following a strict vegetarian or vegan diet, who must ensure sufficient intake through fortified foods or appropriate supplements.

People with chronic digestive disorders

Certain intestinal conditions, such as Crohn’s disease, celiac disease, or chronic stomach infections (like Helicobacter pylori), can damage the intestinal lining and prevent proper absorption of vitamin B12. People with these conditions may suffer deficiencies even if their diet is balanced, making regular medical monitoring necessary.

People on certain medications

Several medications can interfere with vitamin B12 absorption. This is particularly the case for metformin (used to treat type 2 diabetes) and proton pump inhibitors (PPIs), prescribed for gastroesophageal reflux and ulcers. These treatments reduce stomach acid availability or the intestine’s ability to absorb B12, exposing patients to silent deficiencies.

People who have undergone bariatric surgery

Surgical procedures aimed at reducing stomach volume or bypassing part of the intestine, such as gastric bypass, can severely compromise nutrient absorption, especially that of vitamin B12. These patients usually require lifelong supplementation, often via injections, to avoid complications related to prolonged deficiency.

HOW TO DETECT A VITAMIN B12 DEFICIENCY?

Detecting a vitamin B12 deficiency can sometimes be complex, as clinical signs are not always immediate or specific. In many cases, symptoms are subtle, progressive, or mistakenly attributed to other issues such as stress, aging, or lack of sleep. This is why biological testing plays a key role in diagnosis. Early screening helps prevent sometimes irreversible complications, especially neurological ones.

Measuring vitamin B12 levels in the blood

The first recommended test in case of suspected deficiency is a plasma vitamin B12 assay. This test, carried out on a fasting blood sample, measures the total circulating B12 concentration in the body. A level below 200 picograms per milliliter (pg/mL) is generally considered a deficiency. A level between 200 and 400 pg/mL is often deemed borderline, requiring additional analyses to confirm or rule out a functional deficit.

However, it is important to note that this measurement does not always reliably reflect cellular reserves of B12. Some individuals may present “normal” levels despite suggestive symptoms, particularly in cases of inflammation or absorption disorders.

Complementary biological markers

When blood vitamin B12 levels are inconclusive, two additional biological markers can be tested:

Homocysteine: an amino acid whose level increases in cases of vitamin B12 deficiency, but also in folate or vitamin B6 deficiencies. Elevated homocysteine may indicate a functional B12 deficit, especially in older adults or those with cardiovascular disease.

Methylmalonic acid (MMA): a more specific marker. In cases of B12 deficiency, methylmalonic acid levels rise in both blood and urine. Elevated MMA is considered an early and sensitive indicator of deficiency, even when B12 levels appear normal.

These tests help refine diagnosis and assess severity, particularly in cases of malabsorption or in patients on long-term treatments that may mask a deficiency.

The importance of clinical diagnosis

Beyond lab tests, clinical symptom assessment is crucial. Unusual fatigue, memory problems, a sore tongue, tingling in the extremities, or balance issues may point to a vitamin B12 deficiency. Neurological examination, especially in older adults, can also reveal suggestive signs even before biological markers rise significantly.

SHOULD YOU TAKE VITAMIN B12 SUPPLEMENTS?

Vitamin B12 supplementation is sometimes essential, especially for people at higher risk of deficiency. While a balanced diet including animal products is usually sufficient to cover the needs of most people, certain situations make dietary intake insufficient or poorly absorbed. In these cases, taking supplements becomes not only useful but often indispensable.

When is supplementation necessary?

Supplementation with vitamin B12 is recommended in the following situations:

  • Strict vegan or vegetarian diets, without regular intake of animal products or fortified foods
  • Chronic digestive conditions impairing absorption (Crohn’s disease, celiac disease, atrophic gastritis, etc.)
  • Digestive surgery, particularly bariatric surgery
  • Long-term use of certain medications (metformin, proton pump inhibitors)
  • Elderly people with reduced digestive absorption
  • Pregnant or breastfeeding women following a restrictive diet


In these cases, food alone cannot provide sufficient or properly absorbed vitamin B12, making supplementation essential to prevent deficiencies in the medium or long term.

What forms are available?

Vitamin B12 comes in several dosage forms, allowing supplementation to be tailored to individual needs:

  • Oral tablets: often dosed between 250 µg and 1000 µg, suitable for those able to absorb the vitamin at the intestinal level. This is the most common and accessible form for prevention.
  • Sublingual drops: taken under the tongue, they allow rapid absorption via the oral mucosa, partly bypassing intestinal absorption issues. They are appreciated for ease of use.
  • Intramuscular injections: prescribed in cases of severe deficiency or major absorption problems, they ensure rapid restoration of B12 levels. Often used as an initial treatment, then followed by oral supplementation if possible.



What chemical forms are used?

Vitamin B12 can be administered in different chemical forms, the most common being:

  • Cyanocobalamin: a synthetic form of vitamin B12, valued for its stability and widely used in supplements. It is well tolerated by most people and effective at restoring reserves.
  • Methylcobalamin: a naturally active form of vitamin B12, directly usable by the body without conversion. Sometimes preferred for its antioxidant properties and potentially better bioavailability.
  • Hydroxocobalamin: often used in medical settings, especially via injection, it has a longer half-life than cyanocobalamin and may be preferred for long-term treatments.



Should you supplement without medical advice?

Although vitamin B12 has very low toxicity, it is recommended not to start prolonged supplementation without a clear indication or medical advice. If in doubt, a simple blood test can confirm whether supplementation is truly necessary. However, for vegans or those who have undergone digestive surgery, supplementation should be systematic and continuous.

WHAT ARE THE RECOMMENDED DAILY INTAKES?

Vitamin B12 requirements vary depending on age, sex, and specific physiological situations such as pregnancy or breastfeeding. Although this vitamin is needed in very small amounts, its vital role in cellular, nervous, and blood health makes it essential to ensure adequate daily intake.

Recommendations for the general population

Official guidelines for daily intakes aim to ensure proper body function and prevent B12 deficiencies. For a healthy adult, the needs are estimated at 4 micrograms (µg) per day. This threshold takes into account the natural loss of the vitamin and the variability in absorption efficiency from one person to another.

These recommendations also apply to adolescents from the age of 15. Before this age, requirements are slightly lower but gradually increase throughout childhood.

Increased needs during pregnancy

During pregnancy, vitamin B12 needs rise to support fetal development and maternal tissue growth. The vitamin plays a crucial role in cell division, embryonic growth, and the prevention of neural tube defects. The recommended intake during pregnancy is 4.5 µg per day.

An uncorrected deficiency during pregnancy can have consequences on the baby’s neurological development, which is why adequate nutritional monitoring is essential, particularly for women with insufficient intakes or those following a vegan diet.

Recommendations for breastfeeding women

Breastfeeding mobilizes maternal B12 reserves to ensure sufficient levels in breast milk. To meet the needs of both mother and child, the recommended intake increases to 5.5 µg per day during this period. Supplementation is recommended if there is any doubt about adequate intake, especially for vegetarian women or those with digestive issues.

Should intake be adjusted based on age or health condition?

In older adults, even though the official recommendations are not increased, common absorption issues in this population make closer monitoring or even systematic supplementation necessary. Indeed, while recommended intakes remain the same, the actual amount absorbed can be significantly lower.

Finally, certain specific situations — such as digestive surgery, chronic inflammatory diseases, or long-term medication — also require an adaptation of B12 intake, most often through supplementation, to compensate for losses or impaired absorption.

IS VITAMIN B12 TOXIC IN EXCESS?

Vitamin B12 is one of the safest vitamins to consume, even at doses well above the recommended intake. Unlike fat-soluble vitamins (such as vitamins A or D), which can accumulate in the body and cause toxicity, vitamin B12 is water-soluble. This means that in case of excess, it is quickly eliminated through urine and stool, without building up in tissues.

Virtually no toxicity

To date, no serious toxic effects have been associated with excessive vitamin B12 intake in humans. Studies on high doses, sometimes several hundred or even thousands of micrograms per day, have not shown significant adverse effects, even over the long term. This is largely explained by the low intestinal absorption rate: the body only takes what it needs, and the surplus is excreted.

As a result, no Upper Intake Level has been set by health authorities, unlike with other micronutrients.

High intakes without proven benefits

Despite this high tolerance, taking very large amounts of vitamin B12 does not provide additional benefits for healthy individuals who already meet their daily requirements. High-dose supplementation is only justified in specific cases: treatment of a diagnosed deficiency, digestive malabsorption, or certain neurological conditions. Outside these indications, such supplementation is more precautionary than necessary.

Some minor possible side effects

Although rare, a few mild side effects have been reported, mainly with high-dose injections: redness, mild digestive discomfort, or isolated allergic reactions. These cases remain anecdotal and affect only a very small portion of the population.

If you are undergoing medical treatment or have a chronic condition, it is recommended to seek medical advice before taking high doses, to avoid any interaction or inappropriate use.

In summary

Vitamin B12 has an outstanding safety profile, making it a well-tolerated vitamin, even with prolonged supplementation. However, as with any nutrient, intake should be tailored to actual needs, rather than consumed excessively without reason.

WHAT IS THE BEST FORM OF SUPPLEMENTATION: ORAL OR INJECTION?

When vitamin B12 supplementation becomes necessary, the question of the mode of administration quickly arises.

Between tablets taken orally, sublingual drops, or intramuscular injections, several options exist, each with advantages depending on the person’s profile, the severity of the deficiency, and the underlying cause. There is no universal solution, but rather an adaptation based on individual needs.

Oral supplementation: simple, effective, and widely used.

In most cases, tablets or sublingual drops are sufficient to correct or prevent a vitamin B12 deficiency. This mode of supplementation is ideal for the following profiles:

those with insufficient dietary intake (for example, vegans),
those without significant absorption issues,
or those requiring long-term supplementation to compensate for moderately reduced intake.

Oral supplements are often offered at high doses (from 250 µg to 1000 µg), since only a small fraction is absorbed passively at the intestinal level. Nevertheless, these supplements generally succeed in restoring B12 levels in the blood without requiring injections, provided the treatment is followed consistently.

Sublingual route: an interesting alternative.

Sublingual drops or tablets, placed under the tongue, allow direct absorption through the oral mucosa. This method partially bypasses the digestive system, which can be beneficial for people with reduced—but not severely compromised—absorption. It combines the ease of use with effectiveness comparable to standard oral supplementation in many cases.

Injections are recommended in cases of severe malabsorption.

When vitamin B12 can no longer be absorbed effectively through the digestive tract, intramuscular injections become the method of choice. They are particularly indicated in the following situations:

severe anemia with neurological symptoms,
pernicious anemia (absence of intrinsic factor),
gastric or intestinal surgery that reduced the absorption surface,
severe malabsorption linked to chronic digestive conditions.

Injections quickly restore B12 reserves, often through an intensive protocol with closely spaced doses, followed by periodic maintenance. They must be prescribed and monitored by a healthcare professional.

How to choose the most suitable form?

The choice between oral supplementation or injection mainly depends on:

the level of deficiency (moderate or severe),
digestive absorption capacity,
the urgency of treatment,
and the patient’s tolerance or personal preference.

For prevention or in cases of mild deficiency, oral supplementation is generally sufficient. However, when neurological symptoms are present or absorption is nearly absent, injections are often preferred, at least at the beginning of treatment.

Ultimately, both forms are effective, provided they are chosen wisely. The most important factor remains acting as soon as the deficiency is identified, since the earlier the intervention, the better the chances of reversing the symptoms.

ARE THERE RELIABLE PLANT-BASED SOURCES OF VITAMIN B12?

The topic of plant-based sources of vitamin B12 is often discussed

Especially by those following a vegetarian or vegan diet. Indeed, B12 is a vitamin naturally found only in animal-based products. A lot of information circulates about supposed plant-based alternatives, but it is essential to distinguish between active and inactive forms of vitamin B12 in order to evaluate their true effectiveness.

No reliable natural plant source.

To date, no plant, seed, or vegetable naturally contains biologically active vitamin B12 for the human body. Some soil bacteria can synthesize B12, but their presence in plants is either nonexistent or too random to constitute a reliable source. Therefore, an exclusively plant-based diet cannot cover daily needs without external intervention.

The case of algae, spirulina, and nori.

Products like spirulina, chlorella, or nori sheets are sometimes presented as plant-based sources of B12. However, research shows that these foods mainly contain vitamin B12 analogues, called “corrinoids,” which the human body cannot properly absorb or use. Worse still, these inactive forms may hinder the use of active B12 by partially blocking its receptors.

As a result, these foods cannot be considered reliable sources, even if they may be rich in other micronutrients.

Fortified foods: a suitable option for vegans.

Currently, foods artificially fortified with vitamin B12 are the only reliable solution for people following a vegan diet. They are mainly found in industrial products such as:

  • plant-based drinks (almond milk, soy milk, etc.),
  • breakfast cereals,
  • meat substitutes,
  • certain nutritional yeasts.

In these products, B12 is added in synthetic form (often cyanocobalamin), and its bioavailability is comparable to that of dietary supplements. However, quantities can vary from one product to another, making it difficult to cover daily needs through fortified foods alone, especially in cases of increased requirements.

Supplementation: the most reliable solution.

For all those who do not consume any animal-based products, regular supplementation is essential to prevent the risk of deficiencies, which can sometimes be severe, particularly at the neurological level. Taking B12 supplements (oral or sublingual) is simple, inexpensive, and safe in the long term.

In summary, there is no reliable natural plant-based source of active vitamin B12 for humans. Anyone following a vegan diet must ensure sufficient intake through fortified foods or specific supplements. This vigilance is essential to preserve long-term nervous, cognitive, and cellular health.

WHAT ARE THE SYMPTOMS OF A VITAMIN B12 DEFICIENCY?

Sometimes developing over several months, or even years, the first signs often go unnoticed or are attributed to other causes such as stress, fatigue, or aging. However, if left untreated, a deficiency can progress to serious complications, particularly on a neurological level. It is therefore essential to recognize the symptoms early in order to establish an appropriate diagnosis and treatment.

Persistent fatigue and weakness

One of the most common signs of a B12 deficiency is chronic fatigue, often described as an unexplained lack of energy. This sensation may be accompanied by muscle weakness, shortness of breath during exertion, and an overall decline in vitality. These symptoms are linked to an insufficient production of red blood cells, which are essential for transporting oxygen throughout the body.

Sensory disturbances: numbness and tingling

Vitamin B12 is crucial for the proper functioning of the nervous system. In cases of deficiency, it is not uncommon to experience tingling sensations or numbness in the hands, feet, or legs. These issues are caused by the progressive damage to the myelin sheath that protects the nerves. Without proper treatment, this damage can become irreversible.

Memory and concentration problems

A prolonged B12 deficiency can also affect cognitive functions. Affected individuals often report memory problems, poor concentration, mental confusion, or difficulty organizing their thoughts. These signs can be particularly pronounced in older adults, where deficiency may mimic the early symptoms of dementia.

Anemia: paleness, shortness of breath, and dizziness

On a blood level, a B12 deficiency leads to megaloblastic anemia, characterized by abnormally large and ineffective red blood cells. This form of anemia manifests as pale skin, quick onset of breathlessness, dizziness, or a lightheaded feeling when changing positions. It may also be accompanied by an accelerated heart rate.

Mood disorders and depression

Vitamin B12 is involved in the synthesis of neurotransmitters such as serotonin and dopamine, which regulate mood. A deficiency can therefore result in mood swings, irritability, loss of motivation, or even a depressive state. These signs are sometimes among the first to appear, especially in younger individuals or women.

Severe neurological damage in prolonged deficiency

When deficiency persists, it can cause serious neurological damage: loss of coordination, balance problems, unstable gait, difficulty speaking or swallowing. In severe cases, irreversible lesions may affect the spinal cord, compromising mobility and sensory perception.

Ultimately, a lack of vitamin B12 can disrupt multiple body functions, ranging from simple fatigue to severe neurological impairments. The diversity and gradual onset of symptoms justify heightened vigilance, especially among at-risk populations. An early diagnosis and appropriate supplementation generally lead to rapid improvement, and in many cases, full recovery when treatment is initiated in time.

COACH'S TIPS

If you are vegan, it is important to take Vitamin B12 supplements. At QNT, you’ll find vitamin B12 in Daily Vitamin, in Multivitamin Men’s, and in Multivitamin Women’s.

Yves Bondroit coach for QNT

Posted in: Our tips

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