Should You Take B12 Every Other Day If Levels Are Too High?
If your vitamin B12 levels are elevated (>1,000 pg/mL or >738 pmol/L), you should stop supplementation entirely rather than reduce frequency, as persistently elevated B12 levels have been associated with serious underlying conditions including solid tumors, hematologic malignancies, and increased cardiovascular mortality risk. 1, 2
Understanding Elevated B12 Levels
High B12 levels are not benign and warrant investigation rather than dose adjustment:
- Persistently elevated B12 (>1,000 pg/mL on two separate measurements) has been linked to solid tumors of the lung, liver, esophagus, pancreas, and colorectum, as well as hematologic malignancies like leukemia and bone marrow dysplasia 1, 2
- Elevated B12 can also indicate renal failure, liver diseases including cirrhosis and acute hepatitis, or alcohol use disorder 2
- Unlike water-soluble vitamins where excess is simply excreted, elevated B12 often signals an underlying pathologic process releasing stored B12 from tissues 2
What You Should Do Instead
Complete cessation of supplementation is the appropriate response:
- Stop all B12 supplementation immediately if levels are >1,000 pg/mL 1
- Repeat B12 measurement in 3 months to confirm whether levels remain elevated without supplementation 3
- If levels remain persistently elevated (>1,000 pg/mL on repeat testing), pursue evaluation for underlying malignancy, liver disease, or renal dysfunction 1, 2
When B12 Supplementation Is Actually Needed
B12 supplementation is only indicated for documented deficiency (<180 pg/mL) or borderline levels (180-350 pg/mL) with elevated methylmalonic acid (>271 nmol/L): 4, 1
- For deficiency without neurological symptoms: hydroxocobalamin 1 mg intramuscularly three times weekly for 2 weeks, then 1 mg every 2-3 months lifelong 4, 5
- For deficiency with neurological involvement: hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement, then 1 mg every 2 months for life 4, 5
- Oral high-dose B12 (1,000-2,000 mcg daily) is equally effective as injections for most patients, including those with malabsorption 5, 6
Critical Pitfalls to Avoid
- Never continue B12 supplementation with elevated levels - this is not a situation where "more is better" and may delay diagnosis of serious underlying disease 1, 2
- Do not simply reduce frequency to every other day - this approach has no evidence base and fails to address the underlying concern of why levels are elevated 1
- Never assume elevated B12 is harmless - it requires the same diagnostic attention as any other abnormal laboratory finding 1, 2
Monitoring Strategy After Stopping Supplementation
- Recheck B12 levels in 3 months after discontinuation 3
- If levels normalize (<1,000 pg/mL), no further supplementation is needed unless deficiency redevelops 1
- If levels remain elevated, pursue workup including complete blood count, comprehensive metabolic panel, liver function tests, and consideration of imaging to evaluate for occult malignancy 1, 2
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