1. Prevents Anemia:
   • Essential for red blood cell formation; deficiency leads to megaloblastic anemia (Mayo Clinic).
2. Supports Neurological Health:
   • Maintains myelin sheath, preventing neuropathy and cognitive decline (Harvard Medical School).
3. Boosts Energy Levels:
   • Plays a key role in energy metabolism by converting food into glucose (Lippincott).
4. Supports Bone Health:
   • Low B12 levels are linked to osteoporosis (Lange).
5. Improves Mood:
   • Involved in serotonin production, reducing the risk of depression (BNF).

Vitamin B12 is naturally found in animal products:

• Meat: Beef, liver, and poultry.
• Fish: Salmon, trout, and tuna.
• Dairy: Milk, cheese, and yogurt.
• Eggs: Particularly the yolk.
• Fortified Foods: Cereals and plant-based milk for vegans.

Deficiency can lead to:

1. Megaloblastic Anemia: Fatigue, weakness, and pale skin.
2. Neurological Symptoms: Numbness, tingling, memory loss, and depression.
3. Gastrointestinal Issues: Loss of appetite, weight loss, and constipation.
4. Mouth Ulcers and Glossitis: Inflamed, red tongue.

Risk Factors for Deficiency:

• Veganism or vegetarianism.
• Pernicious anemia (lack of intrinsic factor).
• Gastrointestinal disorders (e.g., Crohn’s disease, celiac disease).
• Long-term use of proton pump inhibitors (PPIs) or metformin.

• Normal Range: 200–900 pg/mL (Mayo Clinic).
• Deficiency: <200 pg/mL.
• Borderline: 200–300 pg/mL.

Vitamin B12 supplements are available in various forms and concentrations:

1. Cyanocobalamin:
   • Most common synthetic form.
   • Tablets: 500 mcg, 1000 mcg, 2500 mcg.
2. Methylcobalamin:
   • Active form, preferred for neurological support.
   • Tablets: 1000 mcg, 5000 mcg.
3. Sublingual Tablets:
   • Dissolve under the tongue for better absorption.
4. Injections:
   • Hydroxocobalamin or cyanocobalamin for severe deficiency.

1. Treatment of Deficiency:
   • Corrects megaloblastic anemia and neurological symptoms.
2. Pernicious Anemia:
   • Lifelong B12 supplementation required.
3. Vegan and Vegetarian Diets:
   • Prevents deficiency in individuals with limited dietary intake.
4. Off-Label Uses:
   • Fatigue, cognitive decline, and mood disorders (Harvard Medical School).

Dosage depends on the severity of deficiency and formulation:

Oral Tablets:

• Mild Deficiency: 1000–2000 mcg daily for 1–2 months.
• Maintenance: 1000 mcg daily or weekly.

Injections:

• Severe Deficiency: 1000 mcg intramuscularly daily for 1 week, then weekly for 1 month, then monthly (BNF).

Administration Tips:

• Take oral tablets with food for better absorption.
• Sublingual tablets bypass the gastrointestinal tract, ideal for malabsorption issues.

Vitamin B12 is generally safe, but potential side effects include:

• Mild: Diarrhea, itching, or rash.

Rare: Hypokalemia (low potassium) during anemia treatment

• Pregnancy and Breastfeeding: Safe in recommended doses (BNF Category: A).
• Kidney Disease: Avoid high doses of cyanocobalamin due to cyanide content.

Allergies: Rare hypersensitivity to cobalt or cobalamin

1. Metformin:
   • Reduces B12 absorption; monitor levels (Lippincott).
2. Proton Pump Inhibitors (PPIs):
   • Decrease stomach acid, reducing B12 absorption (Lange).
3. Antiepileptics (e.g., phenytoin):
   • May lower B12 levels.
4. Alcohol:
   • Chronic use impairs B12 absorption.

• Cyanocobalamin (most common synthetic form).
• Methylcobalamin (active form).
• Hydroxocobalamin (used in injections).
• Common brand names: Neurobion®, Cobavite®, Methylcobal®.