Your body cannot make vitamin B12 on its own.
La vitamina B12, un micronutriente que el cuerpo humano no puede fabricar por sí mismo, sostiene en silencio tres pilares fundamentales de la vida celular: la formación del ADN, la producción de glóbulos rojos y la integridad del sistema nervioso. Cuando su presencia mengua —ya sea por elección dietética, enfermedad o el paso del tiempo— el cuerpo comienza a enviar señales que van desde el cansancio hasta el deterioro psiquiátrico irreversible. La historia de esta vitamina es, en el fondo, la historia de una dependencia invisible: la que nos une a los alimentos, a las bacterias y a la cadena de vida que nos precede.
- El déficit de B12 no avisa con claridad: la fatiga, el mareo y la palidez se confunden fácilmente con el ritmo agotador de la vida moderna.
- Cuando los síntomas neurológicos aparecen —hormigueo, pérdida de equilibrio, depresión, pérdida de memoria— la deficiencia ya lleva tiempo instalada y el daño puede volverse permanente.
- Veganos, ancianos, personas con enfermedades gastrointestinales y quienes toman medicamentos como metformina u omeprazol forman un grupo de riesgo más amplio de lo que se suele reconocer.
- Durante décadas, el tratamiento dependió de inyecciones; hoy, la suplementación oral en dosis altas ha demostrado ser igual de eficaz, más cómoda y mejor tolerada.
- Los médicos no recomiendan cribados generalizados, pero sí aconsejan que quienes pertenecen a grupos vulnerables consulten sobre sus necesidades antes de que los síntomas dicten la urgencia.
El cuerpo humano no puede sintetizar vitamina B12 por sí solo. Este hecho aparentemente simple explica por qué su deficiencia puede pasar desapercibida durante meses y, sin embargo, desencadenar consecuencias graves. La B12 —también llamada cobalamina— participa en la formación del ADN, en la producción de glóbulos rojos y en el mantenimiento del sistema nervioso. Al no poder fabricarla, dependemos enteramente de lo que comemos.
La vitamina se encuentra de forma natural solo en productos de origen animal: carnes, pescados, mariscos, lácteos y huevos. Esto convierte a veganos y vegetarianos en candidatos evidentes a la deficiencia, pero el riesgo va mucho más allá de la dieta. Las personas mayores con alimentación deficiente, quienes padecen enfermedades como el Crohn o la celiaquía, y los infectados por helicobacter pylori tienen dificultades para absorber o retener la vitamina. Ciertos medicamentos de uso prolongado —omeprazol, metformina, colchicina— agravan el problema al interferir con su absorción.
Cuando los niveles caen, el cuerpo lo manifiesta primero con señales físicas: fatiga persistente, debilidad, mareos, palidez, pérdida de apetito, diarrea e inflamación de la lengua. Pero la deficiencia también erosiona el sistema nervioso. En casos leves aparecen hormigueos y problemas de equilibrio; en casos graves, irritabilidad, depresión, pérdida de memoria y, en los extremos más severos, trastornos psiquiátricos que pueden volverse irreversibles si no se tratan a tiempo.
La vitamina B12 es soluble en agua, por lo que el organismo no puede almacenar excedentes: lo que sobra se elimina por la orina. Esto descarta el riesgo de toxicidad, pero también exige un aporte constante. Curiosamente, solo las bacterias pueden sintetizarla; en los animales, las bacterias intestinales la producen y esta se acumula en sus órganos —de ahí que el hígado y los riñones sean las fuentes más concentradas.
Durante décadas, el tratamiento estándar fueron las inyecciones. Pero desde los años noventa, estudios realizados en Suecia y Canadá demostraron que la suplementación oral en dosis altas es igual de efectiva, mejor tolerada y menos invasiva. Hoy es la opción predominante en la práctica clínica. Los médicos no recomiendan pruebas de detección masiva, pero sí aconsejan que los grupos de riesgo consulten con su médico antes de que los síntomas impongan la urgencia.
Your body cannot make vitamin B12 on its own. This single fact sits at the center of why a micronutrient most people never think about matters enough to warrant a doctor's attention. B12, also called cobalamina, is involved in three critical processes: the formation of DNA, the creation of red blood cells that carry oxygen through your bloodstream, and the maintenance of your nervous system's structure and function. Because your body cannot manufacture it, you must obtain it from outside sources—primarily through food.
The vitamin appears naturally only in animal products: meat from mammals, poultry, fish, certain shellfish, dairy, and eggs. This dietary reality becomes the first clue to understanding who faces the greatest risk. Vegans and vegetarians who consume no animal products are obvious candidates for deficiency. But the problem extends far beyond dietary choice. Elderly people who eat poorly, those with gastrointestinal diseases like Crohn's disease or celiac disease, and people infected with helicobacter pylori bacteria all struggle to absorb or retain adequate B12. Long-term use of certain medications compounds the problem: omeprazol for acid reflux, metformin for diabetes, colestiramina and colchicina all interfere with B12 absorption.
When levels drop, the body begins to fail at the processes B12 enables. A person might feel persistent fatigue and weakness. Dizziness arrives. The skin takes on a pale cast. Appetite disappears. Diarrhea develops. The tongue swells. These are the visible, physical signs. But B12 deficiency also attacks the nervous system, and here the symptoms become more unsettling. Mild cases produce tingling or numbness in the fingers and toes, along with problems of balance and gait. More severe deficiency triggers irritability, depression, memory loss, and difficulty concentrating. In the most extreme cases, psychiatric disorders emerge—conditions that can become irreversible if the deficiency persists untreated.
Dr. Begoña Ortiz Santodomingo, director of the scientific division at Farmasierra, explains that B12 deficiency is both a consequence and a cause of certain diseases. When levels fall, they disrupt DNA synthesis, red blood cell production, and nerve function simultaneously. The vitamin also prevents megaloblastic anemia, a condition that leaves people exhausted and worn down. Because B12 is water-soluble, the body cannot store excess amounts; any surplus simply dissolves and exits through urine. This means toxicity from too much B12 is not a concern, but it also means consistent dietary intake or supplementation is necessary.
Historically, doctors treated B12 deficiency through injections. The vitamin was the last to be identified, discovered accidentally by an English physician studying pernicious anemia. For decades, the parenteral route—needles—remained standard. But in the early 1990s, physicians in Sweden and Canada began experimenting with high-dose oral B12 supplements. The approach worked. Today, oral supplementation is widespread in clinical practice and considered more effective, better tolerated, and less burdensome for patients than injections. The reason B12 exists at all traces back to bacteria. Only bacteria can synthesize the vitamin. In animals, bacteria colonizing the intestines or rumen produce B12, which then accumulates in the animal's organs—which is why liver and kidneys contain the highest concentrations. In humans, our own gut bacteria can synthesize B12, but our bodies cannot use what they produce.
Currently, doctors do not recommend screening the general population for B12 deficiency. Instead, physicians decide on a case-by-case basis whether blood tests are warranted. For vegans and vegetarians without gastrointestinal disease, consultation with a doctor about supplementation is advisable. The conversation has shifted from whether supplementation works to recognizing it as a practical, accessible solution for those at risk.
Citações Notáveis
When B12 levels are low, the body cannot properly carry out the processes it enables, leading to fatigue, weakness, dizziness, and in severe cases, psychiatric disorders that may become irreversible.— Dr. Begoña Ortiz Santodomingo, director of scientific division at Farmasierra
A Conversa do Hearth Outra perspectiva sobre a história
Why does the body bother to need a vitamin it can't make itself?
It's a quirk of evolution. We lost the ability to synthesize B12 somewhere in our past, probably because we were always going to get it from food. But that dependency becomes a problem when food sources disappear from someone's diet or when their body can't absorb it properly.
So it's not just vegans who are at risk?
Not at all. A vegan eating well might absorb B12 fine with supplements. But an elderly person eating meat could still be deficient if they have an ulcer or take certain medications. The absorption is the real bottleneck.
You mentioned psychiatric symptoms. How serious does it get?
Serious enough that it can become irreversible. Depression, memory loss, concentration problems—these can look like other conditions. But if caught early, supplementation reverses them. If you wait too long, some damage sticks.
Why did it take until the 1990s to figure out oral supplements work?
Injections worked, so there wasn't urgent pressure to find alternatives. Once someone tried high-dose oral doses in Sweden and Canada, it became obvious they worked just as well. Now it's the standard because patients prefer it.
Can you actually overdose on B12?
No. It dissolves in water, so excess just leaves your body through urine. You can't accumulate a toxic amount. The risk is only in deficiency, not excess.
Should everyone get tested?
No. Doctors only test people who fit the risk profile or show symptoms. Routine screening of healthy people isn't recommended. But if you're vegan, elderly, or on certain medications, it's worth asking your doctor.