Vitamin B12 – A Key Nutrient for Nervous System Health, Blood, and Energy | UNUVI Blog

What is Vitamin B12?

Vitamin B12, also known as cobalamin, is a chemical compound classified among the group of water-soluble vitamins. Unlike other B vitamins, B12 contains a central cobalt atom in its structure, making it unique from both a chemical and biological standpoint.

It is found naturally only in animal-derived products, meaning that individuals following a vegetarian or vegan diet are particularly at risk for deficiency. The human body cannot synthesize vitamin B12 on its own — it must be obtained externally.

Biologically active forms:

• Methylcobalamin – the natural active form in the brain and nervous system
• Adenosylcobalamin – the mitochondrial active form
• Hydroxocobalamin – often used in injections
• Cyanocobalamin – synthetic form found in supplements and fortified foods

Functions of Vitamin B12 in the Body

Vitamin B12 is involved in many critical metabolic processes, and its role extends far beyond preventing anemia. Below are the main functions of this vitamin, discussed in detail:

• Proper functioning of the nervous system: Vitamin B12 is essential for the formation and maintenance of myelin sheaths that surround nerve fibers. Myelin acts like insulation on electrical wires — without it, nerve signals become distorted or lost.
• Red blood cell production: B12 is critical for cell division occurring in the bone marrow where red blood cells are produced. Its deficiency leads to the production of abnormally large red cells (megaloblasts), resulting in megaloblastic anemia.
• DNA synthesis and cell division: B12 is involved in DNA methylation and the conversion of homocysteine into methionine, which is necessary for the synthesis of purines and pyrimidines — fundamental units of DNA and RNA.
• Regulation of homocysteine levels: Homocysteine is an amino acid whose excess can damage blood vessels and increase atherosclerosis risk. B12, together with folic acid and vitamin B6, converts homocysteine into methionine.
• Impact on cognition and mood: Vitamin B12 influences the synthesis of neurotransmitters such as serotonin and dopamine, potentially improving mental well-being and cognitive performance.
• Immune system support: B12 affects the activity of NK (natural killer) cells and T lymphocytes, supporting the body’s ability to fight infections.

Symptoms and Consequences of Vitamin B12 Deficiency

Vitamin B12 deficiency may develop slowly and insidiously, with symptoms often being nonspecific, making diagnosis delayed. Early signs are frequently mistaken for chronic fatigue, stress, or even depression. However, long-term deficiency of this vitamin can lead to serious, irreversible neurological and hematological disorders.

Early Symptoms of Deficiency

Initial symptoms are usually subtle, yet significant:

• Fatigue and weakness (even with adequate sleep)
• Concentration difficulties (“brain fog”)
• Pale skin and mucous membranes
• Headaches
• Decreased appetite
• Mood disorders

A study published in “American Family Physician” (2017) described cases where B12 deficiency manifested only as fatigue and irritability before blood test abnormalities appeared.

Neurological Symptoms

Vitamin B12 plays a key role in proper nerve conduction. Its deficiency may lead to:

• Numbness and tingling in limbs (paresthesias)
• Muscle weakness
• Impaired balance and coordination
• Walking difficulties
• Memory disturbances
• Vision problems (optic nerve neuropathy)
• Nerve atrophy and demyelination

A review published in “The New England Journal of Medicine” (2013) found that neurological symptoms may appear even when hemoglobin and hematocrit levels are normal, meaning that absence of anemia does not rule out neurological deficiency.

Hematological Symptoms

The best-known consequence of B12 deficiency is megaloblastic anemia – a type of anemia where red blood cells are abnormally large and inefficient.

Symptoms include:

• Pale skin
• Dizziness
• Shortness of breath
• Tachycardia (rapid heart rate)
• Reduced exercise tolerance

A study in the “British Journal of Haematology” (2021) confirms that megaloblastic anemia may resolve within weeks after starting supplementation, but neurological damage — if present — may be permanent.

Psychiatric Symptoms

B12 deficiency can lead to neuropsychiatric disorders that are often misdiagnosed as depression or anxiety disorders.

Possible symptoms:

• Depression
• Anxiety and restlessness
• Irritability
• Personality changes
• Hallucinations, delusions
• Dementia and symptoms resembling Alzheimer’s disease

A study published in the “Journal of Clinical Psychiatry” (2010) found that even mild B12 deficiency may increase the risk of affective disorders and cognitive decline in older adults.

Laboratory Diagnosis of B12 Deficiency

Standard diagnosis is based on several parameters:

• Serum vitamin B12 concentration (reference values: 200–900 pg/mL)
• Methylmalonic acid (MMA) concentration – elevated in B12 deficiency
• Homocysteine level – elevated may indicate methylation disorder
• Complete blood count – MCV and HGB indicators

Conclusions

Vitamin B12 deficiency is not just a hematological problem — it is also a serious neurological and psychiatric threat. Early diagnosis and intervention (typically via supplementation) can prevent permanent damage. Special vigilance is required for individuals at risk — as will be discussed in the next section.

Who Is Most at Risk of Vitamin B12 Deficiency?

Vitamin B12 deficiency can affect anyone, but there are specific groups of people for whom the risk is significantly elevated. In many cases, the cause is not insufficient dietary intake but rather absorption or metabolic disorders.

1. Vegans and Vegetarians

Why they are at risk:
Vitamin B12 is found naturally only in animal-based foods. A plant-based diet, even well-balanced, does not supply this vitamin in sufficient amounts.

A study conducted in Germany and published in the “European Journal of Nutrition” (2021) found that as many as 92% of vegans and 77% of vegetarians do not meet the recommended intake of vitamin B12 without supplementation.

Conclusion:
Vegans should necessarily supplement vitamin B12 in oral or sublingual form — preferably methylcobalamin or cyanocobalamin. Fortified plant-based products can support the diet but are not sufficient as the sole source.

2. Older Adults

Why they are at risk:
In individuals over 60, there is a natural decline in stomach acid production and intrinsic factor (Castle’s factor), which impairs B12 absorption.

A meta-analysis in the “Journal of Nutrition, Health & Aging” (2018) found that B12 deficiency affects 20–25% of people over 65, often without clear symptoms.

Conclusion:
Older adults should regularly monitor B12 levels and, if necessary, take supplements — often in the form of oral tablets, sublingual sprays, or injections, especially if absorption is impaired.

3. People with Gastrointestinal Disorders

Why they are at risk:
Diseases that damage the stomach lining (such as atrophic gastritis or Helicobacter pylori infection), or surgical removal of part of the stomach or small intestine (e.g., gastric bypass), may severely impair vitamin B12 absorption.

• Crohn’s disease
• Celiac disease
• Small intestine bacterial overgrowth (SIBO)
• Pancreatic insufficiency

The American Gastroenterological Association recommends testing B12 levels in patients with Crohn’s disease and those after gastric surgery.

Conclusion:
In these individuals, supplementation is often required in higher doses or in injectable form. Treating the underlying digestive condition is also crucial.

4. People Taking Certain Medications

Which medications affect B12 absorption:

• Metformin – used to treat type 2 diabetes
• Proton pump inhibitors (PPIs) – e.g., omeprazole, pantoprazole
• H2 receptor antagonists – e.g., ranitidine
• Long-term use of antibiotics

A study in “Diabetes Care” (2020) demonstrated that long-term use of metformin significantly reduces B12 levels in up to 20% of patients.

Conclusion:
People taking these drugs regularly should undergo periodic testing for B12 levels, especially if neurological or hematological symptoms occur.

5. Pregnant and Breastfeeding Women

Why they are at risk:
During pregnancy and breastfeeding, the body’s demand for vitamin B12 increases significantly due to fetal and infant development.

If a woman is vegan or has undiagnosed B12 deficiency, there is a risk of:

• Preterm birth
• Neural tube defects in the fetus
• Impaired cognitive development in the child

A review in “Nutrients” (2021) showed a strong correlation between low maternal B12 levels and reduced psychomotor development in children during the first two years of life.

Conclusion:
Pregnant and breastfeeding women — especially those on restrictive diets — should supplement vitamin B12 and regularly test their levels under medical supervision.

6. People Overusing Alcohol

Why they are at risk:
Chronic alcohol consumption damages the digestive tract lining, impairs nutrient absorption (including B12), and often correlates with poor diet quality.

The Polish Society for Addiction Research reports that 25–30% of alcohol-dependent individuals suffer from macrocytic anemia caused by B12 and folate deficiencies.

Conclusion:
People with alcohol dependence should be regularly screened for B12 deficiency and supplemented under the guidance of a specialist.

7. People with Pernicious Anemia (Addison-Biermer Disease)

What it is:
An autoimmune disease in which the body produces antibodies against intrinsic factor — a protein necessary for vitamin B12 absorption in the small intestine.

Symptoms: identical to B12 deficiency — neurological, psychiatric, and hematological.

Diagnosis is based on detecting anti-intrinsic factor antibodies and Schilling’s test (though rarely used today).

Conclusion:
In this case, vitamin B12 must be administered parenterally (intramuscular injections), as oral absorption is blocked.

Summary

Vitamin B12 deficiency is a serious health issue that can affect people of all ages and diets — not just vegans. The consequences can be severe, especially if not diagnosed early. The most common symptoms include neurological and psychiatric issues, anemia, chronic fatigue, and memory problems.

People at particular risk — such as the elderly, those with digestive disorders, medication users, and pregnant women — should regularly monitor B12 levels and take supplements as needed.

If you suspect a deficiency, consult a doctor, perform laboratory tests, and start supplementation before irreversible changes occur. Vitamin B12 is a key element of long-term mental and physical health.