From the Guidelines
Taking vitamin B12 supplements in doses exceeding 2,000 micrograms is generally considered safe, but rarely necessary except in specific medical situations, such as severe deficiencies or pernicious anemia, as evidenced by the recent guideline summary from the BMJ 1. When considering high doses of vitamin B12, it's essential to weigh the potential benefits against the risks and costs. The recommended daily allowance for most adults is only 2.4 mcg, and therapeutic doses for deficiency typically range from 1,000-2,000 mcg. Some key points to consider:
- High doses of vitamin B12 are sometimes prescribed for severe deficiencies, pernicious anemia, or neurological symptoms, usually administered as injections rather than oral supplements 1.
- Vitamin B12 has low toxicity, but extremely high doses might potentially interact with certain medications like chloramphenicol, metformin, or proton pump inhibitors.
- The effect of vitamin B12 on stroke prevention has been studied, and evidence suggests that B vitamins, including B12, can reduce the risk of stroke by lowering homocysteine levels 1.
- Biochemical and metabolic B12 deficiency are common in patients with stroke, and supplementation with B vitamins, including B12, may be reasonable to reduce stroke risk, especially in patients with renal function impairment or elevated homocysteine levels 1. It's crucial to consult with a healthcare provider before taking high-dose B12 supplements to determine the appropriate dosage and monitor for potential side effects or interactions.
From the Research
Vitamin B12 Dosage
- The recommended dosage of vitamin B12 varies depending on the study, with some suggesting 1000 micrograms for parenteral regimens 2 and others recommending 500 microg/d of crystalline vitamin B12 for oral therapy 3.
- A study from 2024 suggests that 1 mg of B12 per day, either orally or through injections, may be sufficient for maintenance therapy 4.
Administration Routes
- Different administration routes of vitamin B12, including oral, intramuscular (IM), and sublingual (SL) routes, have been compared in various studies 5, 6.
- A retrospective analysis found that SL administration was superior to IM injections in restoring B12 levels 5.
- A systematic review and network meta-analysis found that all IM, oral, and SL routes of administration can effectively increase vitamin B12 levels, with no significant differences between them 6.
Dosage for Older Adults
- Older adults may require higher doses of vitamin B12 due to decreased absorption and increased prevalence of deficiency 2, 3.
- A study from 2006 suggests that 500 microg/d of crystalline vitamin B12 may be necessary to reverse biochemical signs of vitamin B12 deficiency in older adults 3.