Chronic fatigue, tingling in the arms and legs, difficulty concentrating, and pale skin—these are symptoms that millions of people downplay or mistakenly attribute to overwork and stress. However, for a significant portion of them, the cause may be a deficiency in vitamin B12—a substance essential for red blood cell production, proper nervous system function, and DNA synthesis. According to data from the World Health Organization (WHO), vitamin B12 deficiency affects between 2.5% and as much as 26% of the population in developed countries, depending on the diagnostic criteria used. This percentage is many times higher among vegans and vegetarians, the elderly, and those taking metformin.

Vitamin B12 (cobalamin) is the only vitamin that doesn't occur in a biologically active form in any plant food—making deficiency particularly challenging for the growing population of people limiting or eliminating animal products. In this guide, we explain: what symptoms indicate B12 deficiency, who is most at risk, how to diagnose it, what are the dietary sources, and how to effectively supplement B12—including why vitamin B12 gummies can be a convenient daily option.

Highlights from this article:

Vitamin B12 is essential for red blood cell production, DNA synthesis, and proper functioning of the nervous system – deficiency can cause megaloblastic anemia and irreversible nerve damage.
B12 deficiency does not produce any obvious symptoms for a long time - the stores in the liver may last for 3-5 years, which is why the problem is sometimes diagnosed very late.
Particularly vulnerable groups include: vegans and vegetarians, people over 50 years of age, those taking metformin, people after bariatric surgery and people with stomach diseases (atrophic gastritis, celiac disease).
The daily requirement for B12 in an adult is 2.4 μg (EFSA standards) – but oral supplementation requires doses of 100–1000 μg because absorption through the gastrointestinal tract is limited.
Vegans and vegetarians must absolutely supplement B12 – no plant products contain it in a biologically active form sufficient to meet the daily requirement.

What is vitamin B12 and why is it essential?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin, but it has several unique features. It is the largest and most structurally complex of all vitamins—its molecule contains a cobalt atom, which gives it its characteristic red color. In the human body, B12 performs several critical metabolic functions that no other compound can replace.

Red blood cell production. Vitamin B12 is essential for the proper maturation of red blood cells in the bone marrow. B12 deficiency disrupts DNA synthesis in bone marrow cells, leading to the formation of immature, abnormally large red blood cells (megaloblasts)—hence the name megaloblastic anemia. These red blood cells have a shortened lifespan and reduced oxygen-carrying capacity, causing the typical symptoms of anemia: fatigue, weakness, and shortness of breath on exertion.

Functioning of the nervous system. Vitamin B12 is involved in the synthesis of myelin—the fatty sheath covering nerve fibers, which enables the rapid and efficient conduction of nerve impulses. B12 deficiency leads to demyelination—the gradual destruction of this sheath—which manifests initially as tingling and numbness in the extremities and, in advanced cases, serious neurological and psychiatric disorders. Of particular concern is the fact that nerve damage caused by long-term B12 deficiency may be irreversible, even after vitamin supplementation.

DNA synthesis and cell division. Cobalamin works with folic acid (vitamin B9) to synthesize thymidine—one of the four nucleotides that make up DNA. Without proper B12 levels, every rapidly dividing cell—in the bone marrow, intestinal mucosa, skin, and respiratory epithelium—cannot replicate properly. This explains the wide spectrum of deficiency symptoms.

Homocysteine metabolism. Vitamin B12, along with folic acid and vitamin B6, participates in the conversion of homocysteine to methionine. Elevated blood homocysteine levels (hyperhomocysteinemia) are an independent risk factor for cardiovascular disease, stroke, and dementia. B12 deficiency consistently elevates homocysteine levels, making maintaining them at appropriate levels an important element in the prevention of lifestyle diseases.

9 Symptoms of Vitamin B12 Deficiency You Shouldn't Ignore

Vitamin B12 deficiency is insidious—liver stores can remain sufficient for 3–5 years after stopping vitamin B12 intake, making symptoms develop slowly and easy to dismiss or mistakenly attribute to other causes. Below are nine key warning signs.

1. Chronic fatigue and weakness —this is the most common and nonspecific symptom of B12 deficiency. It results directly from megaloblastic anemia: a lower number of functioning red blood cells means poorer oxygenation of muscles and brain. Fatigue associated with B12 deficiency persists after sleep and is disproportionate to physical exertion.

2. Tingling and numbness in the arms and legs (Paresthesia) is one of the first neurological symptoms of B12 deficiency. Damage to the myelin surrounding peripheral nerves causes abnormal impulse conduction, experienced as tingling, prickling, or a feeling of "sleeping" in the extremities. This symptom is characteristic of B12 deficiency and requires urgent diagnosis, as it may signal developing neuropathy.

3. Pale or yellowish skin Megaloblastic anemia causes pale skin and mucous membranes. At the same time, the breakdown of large, abnormal red blood cells releases bilirubin, which can give the skin a slightly yellowish tint. The combination of pallor and yellowish discoloration is a characteristic, though uncommon, symptom of B12 deficiency.

4. Problems with memory and concentration — the brain is extremely sensitive to B12 deficiency. People with low cobalamin levels often report difficulty concentrating, memory problems, slowed thinking, and a feeling of brain fog. brain fog). In older adults, severe B12 deficiency can manifest as dementia resembling early Alzheimer's disease—which is especially important because the condition is reversible with vitamin supplementation.

5. Mood swings and depression — Vitamin B12 is involved in the synthesis of neurotransmitters, including serotonin and dopamine. Its deficiency can lead to low mood, irritability, anxiety, and in severe cases, depression. A study published in Journal of Psychopharmacology showed a correlation between low B12 levels and a higher risk of depression, especially in older people.

6. Inflammation and burning of the tongue (glossitis) — The tongue of a person with B12 deficiency may be red, swollen, smooth (tongue papillae atrophy), and painful. A burning sensation on the tongue when eating or speaking is a characteristic symptom of vitamin B12 deficiency, although rarely associated with it.

7. Rapid heartbeat and shortness of breath Megaloblastic anemia forces the heart to beat faster to compensate for decreased tissue oxygenation. Palpitations, heart palpitations, and shortness of breath with minimal physical exertion can be symptoms of advanced B12 deficiency—especially concerning in people without other cardiovascular diseases.

8. Balance and coordination disorders — Demyelination of the spinal cord nerves (subacute degenerative myelopathy) is a serious complication of severe B12 deficiency. It manifests as unsteady gait, problems with balance, and motor coordination. This is an emergency condition requiring immediate treatment, as spinal cord damage may be irreversible.

9. Difficulty walking and muscle weakness — associated with damage to peripheral and spinal nerves. People with severe B12 deficiency may experience leg weakness, difficulty getting up from a chair, and progressive mobility problems.

Who is most at risk of vitamin B12 deficiency?

Vitamin B12 deficiency isn't just a problem for people on a plant-based diet—although this group is particularly vulnerable. Many dietary, health, and pharmacological factors increase the risk of deficiency.

Risk group	Cause of B12 deficiency	Estimated risk of shortage
Vegans	Complete elimination of animal products – the only natural source of B12	Very high (up to 86% without supplementation)
Vegetarians	Limited sources of B12 (only dairy and eggs), often insufficient	High (up to 26–47% without supplementation)
People over 50 years of age	Reduced production of stomach acid and intrinsic factor (IF) – essential for B12 absorption	Moderate–high (10–30%)
Taking metformin	Metformin impairs the absorption of B12 in the intestines, especially with long-term use.	Moderate (10–30% after 5+ years of use)
People after bariatric surgery	Reduced absorption surface and intrinsic factor production after gastrectomy	Very high without supplementation (up to 50%)
Celiac disease and Crohn's disease	Damage to the lining of the small intestine impairs B12 absorption	Moderate–high
Atrophic gastritis	Reduced production of HCl and intrinsic factor (necessary for B12 absorption)	Very high
Long-term use of PPIs (proton pump inhibitors, e.g. omeprazole)	Reducing stomach acidity inhibits the release of B12 from dietary proteins	Moderate (when used for over 2 years)

It is worth emphasizing that metformin—a drug commonly used to treat insulin resistance and type 2 diabetes—is one of the most common pharmacological causes of B12 deficiency. A study published in The BMJ (2010) found that long-term metformin use was associated with a 19% increased risk of B12 deficiency. The European Diabetes Association recommends regular monitoring of B12 levels in patients taking metformin for more than 4 years—a practice that is often not followed. FEZI Apple Cider Vinegar at ubucha.pl, combining ACV extract with vitamin B12, are a particularly good choice for this group - people using ACV for insulin resistance and taking metformin supplement two key deficiencies at the same time.

Diagnosis of vitamin B12 deficiency – how to detect it?

B12 deficiency is primarily diagnosed through blood tests. Key diagnostic parameters include serum vitamin B12 levels, a complete blood count (CBC), and homocysteine and methylmalonic acid (MMA) levels, which are markers of functional B12 deficiency.

A serum B12 level below 150–200 pmol/l (200–270 pg/ml) indicates a deficiency requiring supplementation. Borderline values of 200–300 pmol/l are considered subclinical deficiency, which, despite the lack of obvious clinical symptoms, can cause subtle neurological impairment and elevated homocysteine. Many laboratories use a lower limit of normal of 200 pg/ml, but some researchers believe that neurological symptoms may appear at values of 300–400 pg/ml in older individuals or those with risk factors.

Methylmalonic acid (MMA) is a more sensitive marker of functional B12 deficiency than serum cobalamin levels alone—elevated levels indicate that tissues are not receiving sufficient active B12, even if serum levels are within the normal range. MMA is particularly useful in diagnosing subclinical deficiency in older adults. Similarly, homocysteine levels above 15 μmol/L with normal B12 and folate levels suggest functional cobalamin deficiency.

Megaloblastic anemia – what does blood count show?

Blood counts in B12 deficiency show characteristic changes: elevated MCV (mean erythrocyte volume, above 100 fl oz—hence the term macrocytosis), low hemoglobin and hematocrit levels, and macrocytes and hypersegmented neutrophils (with more than five nuclear lobes) visible in the blood smear. These abnormalities, coupled with low B12 levels, confirm the diagnosis of megaloblastic anemia. It's important to remember that folic acid deficiency produces an identical morphological picture, hence the need to measure both vitamins simultaneously.

Natural sources of vitamin B12 in the diet

Vitamin B12 is synthesized exclusively by microorganisms—bacteria and archaea—and is passed on through the food chain to higher organisms through the consumption of animal products, as animals accumulate B12 produced by intestinal bacteria or ingested with food. No plants, fungi, or algae produce biologically active B12, hence the absolute necessity of supplementation for vegans.

Product (100 g portion or standard portion)	B12 content (μg)	% daily requirement (2.4 μg)
Beef liver (85 g)	70.7 μg	2946%
Mussels (85 g)	84.1 μg	3508%
Mackerel (100 g)	8.7 μg	362%
Salmon (100 g)	3.2 μg	133%
Tuna (100 g)	2.5 μg	104%
Beef (100 g)	2.6 μg	108%
Egg (1 pc., approx. 50 g)	0.6 μg	25%
Milk (200 ml)	0.9 μg	37%
Yellow cheese (30 g)	0.3–0.5 μg	12–21%
Plant products (nori, algae, spirulina)	They contain pseudovitamin B12 - a biologically inactive analogue	0% (no active form)

People who eat meat and fish several times a week easily meet their B12 needs—a single serving of beef liver provides enough B12 for a month. This problem arises for people who limit their intake of animal products, take long-term medications that reduce stomach acidity, or have absorption disorders.

Are algae and spirulina sources of B12 for vegans?

This is one of the most frequently perpetuated dietary myths. Spirulina, chlorella, nori, and other algae contain compounds chemically similar to B12 but biologically inactive—so-called pseudovitamins B12 or cobalamin analogues. These analogues not only fail to fulfill the active function of B12 in the body, but can actively block cobalamin receptors and impede the absorption of B12, de facto exacerbating its deficiency. The European Food Safety Authority (EFSA) unequivocally states that algae are not a reliable source of biologically active vitamin B12 for humans. The only effective method of B12 supplementation for vegans is to take synthetic cyanocobalamin or methylcobalamin in the form of a dietary supplement.

Vitamin B12 supplementation – forms, doses and effectiveness

B12 supplementation differs significantly from supplementation of most other vitamins - the required doses are many times higher than the daily requirement, and the choice of form and route of administration depends on the cause of the deficiency.

Forms of vitamin B12 in supplements

Cyanocobalamin This is the most common and cheapest form of B12 found in supplements—chemically stable, well-researched, and effective. Once absorbed, it is converted in the body into its active forms (methylcobalamin and adenosylcobalamin). This is the form used in FEZI gummies, among others.

Methylcobalamin It's an active form of B12 that doesn't require conversion in the body. It's especially recommended for people with the MTHFR gene mutation (which disrupts B vitamin metabolism), although for most people, the difference in effectiveness compared to cyanocobalamin is clinically insignificant.

Hydroxocobalamin is an injectable form - it has a longer duration of action than cyanocobalamin and is preferred for the treatment of severe deficiency requiring rapid correction.

B12 Dosage in Oral Supplements

The paradox of B12 supplementation stems from the specifics of its absorption. Dietary vitamin B12 is absorbed in the ileum with the help of intrinsic factor (IF) produced by stomach cells—but this pathway has limited capacity: a maximum of approximately 1.5–2 μg of B12 per serving. At supplemental doses above 500 μg, the active absorption pathway becomes saturated, and additional amounts of B12 are absorbed passively through diffusion—with a very low efficiency of approximately 1%. This means that a supplement containing 1000 μg of B12 provides the body with approximately 10 μg through passive diffusion plus a maximum of 2 μg through active absorption—a total of approximately 12 μg, or approximately 5 times the daily requirement.

Recommended doses of oral B12 supplementation by group:

Prevention in healthy adults who eat meat — 25–100 μg per day is sufficient as insurance against possible absorption deficiencies.
Vegans and vegetarians — at least 250 μg daily or 2500 μg once a week. Higher oral doses compensate for low passive absorption in the absence of dietary B12.
People over 50 — 500–1000 μg per day, because reduced stomach acidity limits active absorption from food.
People taking metformin — 500–1000 μg daily with long-term metformin therapy.
Treatment of clinical deficiency — 1000 μg daily for at least 3 months orally (or hydroxocobalamin injections in case of severe deficiency with neurological symptoms).

Convenient forms of B12 supplementation – gummies as an alternative to tablets

Traditional B12 supplementation in the form of tablets or capsules can be problematic for people with difficulty swallowing tablets, children, and seniors. Supplemental gummies containing B12 offer an alternative that combines effectiveness with pleasure. FEZI Apple Cider Vinegar Jellies Available at ubucha.pl, they contain cyanocobalamin (vitamin B12) as one of three active ingredients—along with apple cider vinegar extract (1000 mg) and the prebiotic IOS. For those who want to simultaneously support their metabolism (ACV), gut microbiota (IOS), and supplement B12, this is a particularly effective combination.

In a broader sense jelly category ubucha.pl offers various products that support the replenishment of vitamin deficiencies - it is worth checking the current offer and choosing the form best suited to your needs and taste preferences.

How long does it take to correct vitamin B12 deficiency?

The time required to correct B12 deficiency depends on its severity, cause, and the chosen supplementation method. In subclinical deficiency (serum B12 level 150–250 pmol/l without neurological symptoms), regular oral supplementation of 500–1000 μg daily leads to normalization of serum vitamin levels, usually after 4–8 weeks. Blood counts normalize within 6–8 weeks of starting treatment.

For deficiency with neurological symptoms (tingling, gait disturbance, dementia), hydroxocobalamin injections are recommended—the typical regimen is 1 mg intramuscularly every other day for two weeks, then every three months. Neurological symptoms resolve within a few weeks to several months, but in advanced cases (long-term deficiency), they may be only partially reversible. Therefore, early diagnosis and treatment are crucial.

Once the deficiency is corrected, preventative maintenance supplementation should be continued indefinitely in individuals with persistent risk factors (vegans, post-gastrectomy individuals, atrophic gastritis). B12 levels cannot be "overdosed" in the conventional sense—the excess is excreted in the urine, and toxic effects at supplemental doses (up to several mg per day) have not been described in clinical studies.

B12 and fatigue – will a supplement help if your levels are normal?

B12 supplementation is effective and brings a noticeable improvement in well-being—but only in people with a true vitamin deficiency. If B12 levels are normal (above 300 pmol/l) and fatigue stems from other causes (hypothyroidism, iron deficiency anemia, sleep disorders, depression, chronic infections), B12 supplementation will not produce the desired results. Before taking a supplement, it's worth performing laboratory tests to identify the actual cause of fatigue.

Serum B12 testing is available at any diagnostic laboratory in Poland—it costs approximately 30–50 PLN and does not require a referral. If a deficiency or borderline level (200–300 pmol/l) is detected in a person at risk (vegan, someone over 50, taking metformin), supplementation is fully justified even without clinical symptoms, as deficiency detected early is fully reversible.

What are the symptoms of vitamin B12 deficiency?

The most common symptoms of B12 deficiency include chronic fatigue and weakness (resulting from anemia), tingling and numbness in the arms and legs (nerve damage), pale skin, problems with memory and concentration, mood swings and irritability, inflammation of the tongue (glossitis), rapid heartbeat, and problems with balance and gait. Symptoms develop slowly—liver stores of B12 can last for 3–5 years before the first symptoms appear.

Who is most at risk of B12 deficiency?

Particularly vulnerable groups include: vegans (up to 86% without supplementation), vegetarians, people over 50 years of age (reduced production of intrinsic factor), those taking metformin long-term, people after bariatric surgery, with celiac disease, Crohn's disease or atrophic gastritis, as well as those taking PPIs (acid reflux drugs) for more than 2 years.

How much vitamin B12 does an adult need per day?

The daily requirement for a healthy adult is 2.4 μg according to EFSA standards. Pregnant women need 2.6 μg, and breastfeeding women 2.8 μg. Much higher doses (500–1000 μg) are needed for oral supplementation, as only about 1% of the supplement is passively absorbed, and the active pathway via intrinsic factor is saturated at doses above 1.5 μg.

Does B12 deficiency cause fatigue?

Yes. B12 deficiency leads to megaloblastic anemia—a condition in which the bone marrow produces abnormal, large, and nonfunctional red blood cells. Fewer functioning red blood cells mean less oxygenation to the muscles and brain, which manifests as chronic fatigue, weakness, and shortness of breath on exertion. Fatigue resulting from B12 deficiency subsides after a few weeks of supplementation.

What products contain vitamin B12?

Vitamin B12 is found exclusively in animal products. The richest sources include liver (beef, poultry), mussels, mackerel, salmon, tuna, beef, eggs, and dairy products. Plant foods (algae, spirulina, nori) contain pseudovitamin B12—a biologically inactive analogue that does not function as cobalamin and may even block the absorption of active B12.

Do vegans need to supplement B12?

Yes, absolutely. Vegans do not consume any animal products—the only natural source of biologically active B12. Without regular supplementation or consuming fortified products (e.g., fortified plant-based beverages), B12 deficiency in vegans is inevitable—though it can develop slowly over several years. The recommended preventative dose for vegans is at least 250 μg daily or 2,500 μg once a week.

How long does it take to correct B12 deficiency?

With oral supplementation of 500–1000 μg daily, serum B12 levels normalize within 4–8 weeks. Blood counts (anemia) improve after 6–8 weeks. Neurological symptoms resolve more slowly—from several weeks to several months—and may be only partially reversible in long-term, severe deficiency. Prophylactic supplementation should be continued indefinitely in individuals at risk.

Can you overdose on vitamin B12?

Vitamin B12 is a water-soluble vitamin—excess is excreted in the urine and does not accumulate in the body in a toxic manner. No clinical studies have shown adverse effects with supplemental doses of up to several mg per day. Vitamin B12 is considered one of the safest vitamins in terms of the risk of toxicity with supplementation.

Vitamin B12 is essential for a healthy nervous system, blood production, and proper cellular metabolism. Vitamin B12 deficiency—often developing for years without obvious symptoms—can lead to serious, sometimes irreversible health consequences: megaloblastic anemia, peripheral neuropathy, and cognitive impairment. Particularly vulnerable groups—vegans, people over 50, and those taking metformin or PPIs—should have their serum B12 levels checked regularly and take preventative supplements without waiting for symptoms to appear.

When choosing a form of B12 supplementation, it's worth choosing a product that will replenish the vitamin in a pleasant and regular way. ubucha.pl supplement category you will find, among others:. FEZI Apple Cider Vinegar jellies — a product combining vitamin B12 with ACV extract and the prebiotic IOS, ideal for those seeking comprehensive energy metabolism, gut health, and B12 supplementation in one daily serving. They are a particularly good choice for those using ACV for insulin resistance and taking metformin—two groups in which B12 deficiency is particularly common and clinically significant.