Vitamin B12 tablets
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Vitamin B12 (Cobalamin) Tablets
What is Vitamin B12?
Vitamin B12 (cobalamin) is an essential water-soluble vitamin critical for:
- DNA synthesis and red blood cell formation
- Neurological function (myelin sheath maintenance)
- Homocysteine metabolism
Who Needs B12 Supplementation?
High-risk groups for deficiency:
| Group | Reason |
|---|---|
| Strict vegetarians/vegans | B12 found almost exclusively in animal products |
| Older adults | Reduced gastric acid impairs food-bound B12 absorption |
| Post-bariatric surgery patients | Altered GI anatomy reduces absorption |
| Pernicious anemia patients | Lack of intrinsic factor |
| Gastrectomy / IBD patients | Reduced absorptive capacity |
| Metformin users | Drug reduces B12 absorption |
| Proton pump inhibitor (PPI) users | Reduced gastric acid |
| Nitrous oxide exposure | Inactivates B12 |
(Harrison's Principles of Internal Medicine, 21st Ed., p. 12699)
Symptoms of Deficiency
- Hematological: Megaloblastic (macrocytic) anemia — fatigue, pallor, shortness of breath
- Neurological: Peripheral neuropathy, subacute combined degeneration of the spinal cord (weakness, ataxia, loss of vibration/position sense)
- Psychiatric: Depression, cognitive impairment, memory loss
- Other: Glossitis, elevated homocysteine
Diagnosing Deficiency
- Serum B12: First-line, but can be normal even with true deficiency
- Serum methylmalonic acid (MMA): More sensitive marker of functional B12 deficiency — elevated when B12 is deficient
- Homocysteine: Also elevated in B12 deficiency (less specific)
Serum B12 alone may miss deficiency — consider measuring MMA, with or without homocysteine, in symptomatic patients or those with risk factors. (Bariatric Surgery Nutritional Guidelines, p. 26)
Dosing of B12 Tablets
| Indication | Dose | Route |
|---|---|---|
| Maintenance / Prevention | 350–1,000 µg/day | Oral (tablet, sublingual, or disintegrating) |
| Treatment of deficiency | 1,000–2,000 µg/day | Oral |
| Parenteral (if oral fails) | 1,000 µg/month OR 1,000–3,000 µg every 6–12 months | IM or SC injection |
| Intranasal | Available as an alternative | Intranasal spray |
(Bariatric Surgery Nutritional Guidelines, Grade A; BEL 1, p. 26)
Key point: High-dose oral B12 works even in pernicious anemia because ~1% of B12 is absorbed passively (without intrinsic factor) — so doses of 1,000–2,000 µg/day can overcome the absorption defect.
Forms of Oral B12
| Form | Notes |
|---|---|
| Cyanocobalamin | Most common, stable, inexpensive |
| Methylcobalamin | Active form, preferred by some for neurological symptoms |
| Hydroxocobalamin | Longer-acting, used parenterally |
| Adenosylcobalamin | Active mitochondrial form |
Monitoring Treatment
- Recheck serum B12 (and MMA if previously elevated) after 1–3 months of treatment
- Neurological symptoms may take months to improve; irreversible damage is possible if deficiency is prolonged
- Post-bariatric surgery patients: check B12 every 3 months in the first year, then annually
Safety
Vitamin B12 is very safe — it is water-soluble and excess is excreted in urine. No established upper tolerable intake limit exists. Side effects are rare and typically confined to injectable forms (injection site reactions). Oral tablets have an excellent safety profile.
Clinical note: Always treat the underlying cause of deficiency alongside supplementation where possible (e.g., stopping offending medications, addressing malabsorption).
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