Chapter 1. Introduction
The author explains why vitamin B12 deserves a separate book: its deficiency is widespread but remains one of the most underestimated causes of chronic health problems—from fatigue and depression to cognitive decline and anemia. The main danger is that symptoms develop slowly and are often attributed to stress or aging, while laboratory "norms" do not reflect the true state of the cells.
He explains how vitamin B12 works: it is a complex molecule involved in DNA synthesis, nervous system function, and methylation, without which energy metabolism and brain functions are disrupted.
Vitamin B12 is synthesized not by plants or animals, but by bacteria living in the soil and the intestines of animals. In modern conditions—with antiseptics, antibiotics, purified water, and vegetarian diets—humans no longer receive these microorganisms naturally. Therefore, deficiency has become a widespread problem in the West, especially among the elderly, vegans, and people with absorption disorders. The authors emphasize: B12 is not just a vitamin, but a critical element for neuron survival and longevity.
Chapter 2. The Basics
The history of the discovery of vitamin B12 began with studies of fatal anemia in dogs, which were saved by raw liver. Later, scientists isolated the active substance—cobalamin, a unique vitamin containing a cobalt atom. It is necessary for DNA synthesis, nervous system function, and the conversion of homocysteine to methionine, supporting normal metabolism and brain health.
The daily requirement is small—just a few micrograms—but the body's stores can last for years, so deficiency symptoms develop slowly. However, in special situations (pregnancy, old age, stress, veganism, gastrointestinal diseases, use of PPIs or metformin), the need increases sharply.
Normal blood levels do not always reflect true status: even "normal" values with elevated homocysteine or methylmalonic acid (MMA) can indicate deficiency. Sources of B12 are animal products (meat, fish, eggs, liver). Popular "vegan sources" like spirulina or fermented soy products are a myth: they contain inactive analogs (pseudo-B12) that are not absorbed.
Causes of deficiency include low dietary intake, absorption disorders, autoimmune gastritis, bacterial imbalance, parasites, and medications.
The disease develops in stages: from hidden cellular deficiency to irreversible neurological damage. The most dangerous manifestations are spinal cord damage, optic nerve atrophy, dementia, and psychoses, which can only be prevented by timely diagnosis and correction of B12.
Chapter 3. Putting It All Together
The author brings together all aspects of the role of vitamin B12 and shows how its deficiency affects every system in the body. This vitamin is essential for blood formation, DNA synthesis, nerve function, brain activity, and energy metabolism. When it is lacking, all cells suffer—from bone marrow to neurons.
B12 and anemia. A lack of B12 disrupts red blood cell formation, leading to megaloblastic anemia: fatigue, shortness of breath, pallor, and rapid heartbeat.
B12 and the nervous system. Deficiency leads to the destruction of myelin—the protective sheath of nerves.
The heart and blood vessels. Without sufficient B12, homocysteine levels rise—a toxic metabolite that damages blood vessels and increases the risk of heart attacks, strokes, and thrombosis. Correcting the deficiency reduces inflammation and improves endothelial health.
The immune, endocrine, and reproductive systems. Vitamin B12 is involved in the formation of immune defense proteins, affects fertility, and hormonal balance. In men, deficiency can cause reduced spermatogenesis; in women, menstrual irregularities and infertility. In pregnant women, a deficiency increases the risk of miscarriage, neural tube defects, and anemia in the fetus, while in breastfeeding women, it can cause developmental delays in infants.
Skin, muscles, and metabolism. A lack of B12 manifests as dry skin, pigmented spots, bruising, muscle weakness, and pain. After surgeries, deficiency often worsens due to impaired absorption.
Chapter 4. The Diagnosis of Vitamin B12 Deficiency
The author addresses both doctors and patients, emphasizing that despite the fact that B12 deficiency is easy to detect, it often remains unrecognized for years. The reason is outdated diagnostic standards and blind trust in laboratory "norms" that do not reflect the state of cellular metabolism.
How deficiency is usually diagnosed. In practice, doctors often rely solely on serum B12 levels, but this indicator is unreliable: it can be normal even with pronounced neurological symptoms. Often, the diagnosis is made only after the onset of anemia or neurological disorders, when damage becomes difficult to reverse.
The best tests. Tests for methylmalonic acid (MMA) and homocysteine are considered more accurate—they reflect the functional deficiency of the vitamin in the cells. It is also optimal to measure the active form—holotranscobalamin (holo-TC), which shows how much B12 is actually available for tissues. These tests allow for early detection of deficiency, even before anemia.
Additional methods. In some cases, tests for antibodies to intrinsic factor (for diagnosing pernicious anemia), determining folate and iron levels, as well as a complete blood count to assess red blood cell size (MCV) can be useful.
Other rare tests, such as the Schilling test, are now rarely used due to complexity and limited informativeness.
The main conclusion of the author is the diagnosis of B12 deficiency should be clinical: the doctor must consider not only the numbers but also the patient's symptoms. It is better to start treatment with questionable indicators than to wait for nerve damage to become irreversible.
Chapter 5. How Is B12 Deficiency Treated?
The main principle of therapy is rapid and adequate replenishment of vitamin B12 stores to prevent irreversible damage to the nervous system. Treatment is safe, inexpensive, and effective, but requires an individualized approach: dosage and form depend on the cause of the deficiency, age, and gastrointestinal condition.
Forms of vitamin B12. There are four main forms: cyanocobalamin, methylcobalamin, hydroxocobalamin, and adenosylcobalamin. The first two are the most common. Methyl- and adenosylcobalamin are natural, biologically active forms that the body can use immediately. Hydroxocobalamin stays in the blood longer and is often used in injection therapy.
Methods of administration. B12 can be administered as injections, tablets, sublingual forms, drops, or sprays. In cases of absorption disorders or severe deficiency, injections are preferred, which bypass the gastrointestinal tract. In less severe cases, high oral doses—1000–2000 mcg per day—are effective.
Side effects are extremely rare and usually related to individual intolerance to excipients. Vitamin B12 is non-toxic even in very high doses: excess is excreted in urine. Conversely, too low doses or a short course do not allow for replenishing intracellular deficiency.
The authors emphasize: if deficiency is suspected, it is better to start treatment immediately—there is no harm in this, and the benefits can be enormous, especially in the presence of neurological symptoms.
Chapter 6. The Misdiagnosis of B12 Deficiency
A widespread problem is incorrect or delayed diagnosis. Doctors often confuse B12 deficiency with other diseases, as its symptoms are nonspecific and can mimic dozens of pathologies. People receive antidepressants, painkillers, or antipsychotics for months or years without addressing the true cause.
Misdiagnosed conditions. B12 deficiency is often masked as depression, anxiety disorders, chronic fatigue syndrome, multiple sclerosis, diabetic neuropathy, anemia of unclear origin, fibromyalgia, dementia, Alzheimer's disease, and even schizophrenia. In elderly patients, such errors are particularly common because cognitive decline is mistaken for aging.
The authors urge doctors to consider B12 deficiency as a possible cause of any neurological or psychiatric disorders before prescribing medication. A simple check and correction of B12 can restore normal well-being without "lifetime" diagnoses.
