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What is the dosage of vitamin B 12 in a healthy adult as supplements

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Answer

Vitamin B12 (cobalamin) supplement dosage for a healthy adult depends on the purpose - general maintenance vs. correcting deficiency:
Recommended Dietary Allowance (RDA) - healthy adults
  • 2.4 mcg/day (this covers normal dietary needs for most healthy adults)
  • Pregnancy: 2.6 mcg/day
  • Lactation: 2.8 mcg/day
Over-the-counter maintenance supplement
  • Many multivitamins and standalone B12 supplements contain 25-100 mcg/day, which is well above the RDA but considered safe since B12 has low toxicity risk and excess is excreted in urine (absorption also becomes limited at high doses via intrinsic-factor-mediated uptake).
Higher doses used for deficiency or at-risk groups
  • Mild prevention in at-risk groups (e.g., older adults with reduced absorption, strict vegans): 500-1000 mcg/day oral, sometimes used empirically
  • Confirmed deficiency: typically 1000-2000 mcg/day oral, or intramuscular injections (e.g., 1000 mcg IM) in regimens such as daily/weekly for a few weeks followed by monthly maintenance, depending on the cause and severity
Key points
  • No established Tolerable Upper Intake Level (UL) exists for B12 because of its low toxicity - even doses far above the RDA have not shown clear harm in a healthy person with normal kidney function.
  • Adults over 50, vegans/vegetarians, and people with absorption disorders (pernicious anemia, gastric bypass, metformin use, PPI use) often need higher or injectable doses since oral absorption can be impaired.
  • If you're taking it simply for general health maintenance with no diagnosed deficiency, 25-100 mcg/day orally is a reasonable and common supplement dose; if you suspect deficiency (fatigue, neuropathy, macrocytic anemia), that should be confirmed with a blood test (serum B12, sometimes with methylmalonic acid) before deciding on high-dose or injectable therapy.
If you let me know your specific reason for supplementing (general health, vegan diet, confirmed low levels, absorption issue), I can narrow this down further.

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