Vitamin B12
Also known as: Cobalamin, Cyanocobalamin, Methylcobalamin, B12
Vitamin B12 is a water-soluble vitamin essential for red blood cell formation, neurological function, and DNA synthesis. Unlike other water-soluble vitamins, B12 can be stored in the liver for years. It is found naturally only in animal-derived foods, making supplementation important for vegans and vegetarians.
Benefits
Essential for red blood cell production — prevents megaloblastic anemia. Critical for nervous system health and myelin sheath maintenance. Required for DNA synthesis and cell division. Supports brain function, memory, and concentration. May help reduce homocysteine levels, a risk factor for cardiovascular disease. Supports energy metabolism — often associated with reduced fatigue.
Recommended Dosage
RDA: 2.4 mcg/day for adults. Common supplement doses: 500–1,000 mcg daily (higher doses used because absorption is limited). Sublingual forms (dissolved under the tongue) may bypass absorption issues. Injections (1,000 mcg monthly or more frequently) are used for malabsorption conditions. Methylcobalamin and adenosylcobalamin are the active forms; cyanocobalamin is most common in supplements.
Food Sources
Meat (especially beef liver and organ meats), fish (salmon, trout, tuna, sardines), shellfish (clams, mussels), poultry, eggs, dairy products (milk, cheese, yogurt), fortified nutritional yeast, fortified cereals, fortified plant-based milks.
Side Effects
Generally very safe even at high doses — excess is excreted in urine. Rarely: Mild diarrhea, itching, rash, headache. Injectable B12: Pain or redness at injection site, mild diarrhea, temporary swelling. Extremely rare: Anaphylaxis with injections (almost exclusively with cyanocobalamin). High doses are not known to be toxic.
Interactions
Metformin reduces B12 absorption — monitor levels if taking long-term. Proton pump inhibitors (PPIs) and H2 blockers reduce stomach acid needed for B12 absorption. Colchicine reduces B12 absorption. Chloramphenicol may interfere with red blood cell response to B12 supplementation. Excessive alcohol consumption impairs B12 absorption.
Warnings
B12 deficiency can cause irreversible neurological damage if untreated — early detection is important. Vegans and strict vegetarians must supplement as there are no adequate plant sources. People over 50 may have reduced ability to absorb B12 from food. Those who have had gastric surgery, Crohn's disease, or celiac disease are at higher risk for deficiency. Folic acid supplementation can mask B12 deficiency anemia, allowing neurological damage to progress.
Deficiency Symptoms
Fatigue and weakness, megaloblastic anemia, numbness and tingling in hands and feet (peripheral neuropathy), difficulty walking and balance problems, cognitive difficulties (memory loss, confusion), mood changes (depression, irritability), glossitis (swollen, inflamed tongue), pale or jaundiced skin. Severe deficiency: Dementia-like symptoms, vision disturbances, paranoia.
Frequently Asked Questions
What are the benefits of Vitamin B12?▼
Essential for red blood cell production — prevents megaloblastic anemia. Critical for nervous system health and myelin sheath maintenance. Required for DNA synthesis and cell division. Supports brain function, memory, and concentration. May help reduce homocysteine levels, a risk factor for cardiovascular disease. Supports energy metabolism — often associated with reduced fatigue.
What is the recommended dosage for Vitamin B12?▼
RDA: 2.4 mcg/day for adults. Common supplement doses: 500–1,000 mcg daily (higher doses used because absorption is limited). Sublingual forms (dissolved under the tongue) may bypass absorption issues. Injections (1,000 mcg monthly or more frequently) are used for malabsorption conditions. Methylcobalamin and adenosylcobalamin are the active forms; cyanocobalamin is most common in supplements.
What foods contain Vitamin B12?▼
Meat (especially beef liver and organ meats), fish (salmon, trout, tuna, sardines), shellfish (clams, mussels), poultry, eggs, dairy products (milk, cheese, yogurt), fortified nutritional yeast, fortified cereals, fortified plant-based milks.
What are the side effects of Vitamin B12?▼
Generally very safe even at high doses — excess is excreted in urine. Rarely: Mild diarrhea, itching, rash, headache. Injectable B12: Pain or redness at injection site, mild diarrhea, temporary swelling. Extremely rare: Anaphylaxis with injections (almost exclusively with cyanocobalamin). High doses are not known to be toxic.
What are the symptoms of Vitamin B12 deficiency?▼
Fatigue and weakness, megaloblastic anemia, numbness and tingling in hands and feet (peripheral neuropathy), difficulty walking and balance problems, cognitive difficulties (memory loss, confusion), mood changes (depression, irritability), glossitis (swollen, inflamed tongue), pale or jaundiced skin. Severe deficiency: Dementia-like symptoms, vision disturbances, paranoia.
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Supplement Disclaimer
This supplement information is for educational purposes only and should not replace professional medical advice. Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a healthcare provider before starting any supplement, especially if you are pregnant, nursing, taking medications, or have a medical condition.