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Vitamin B12
What Vitamin B12 is, what the NIH ODS fact sheet says the evidence supports, typical doses, timing, and the cautions that come with it.
Supplements are not medicines and this page is not medical advice. Doses that help one person can harm another — with medicines, kidney or liver conditions, pregnancy, or before surgery, talk to a clinician before starting anything. More is not better.
What it is
A vitamin needed for nerve function and red blood cell formation; only found reliably in animal foods.
What the evidence supports
ODS: treats deficiency, which is common in vegans, older adults and after stomach surgery.
Dose and timing
RDA: 2.4 mcg per day. Any time; absorbed with or without food.
Cautions
Vegans need a reliable source (supplement or fortified foods) — deficiency develops slowly and can be permanent if untreated.
Interactions are the hidden risk: supplements can change how medicines work and vice versa. Give your clinician the full list before anything else.
Source: NIH Office of Dietary Supplements — Vitamin B12 fact sheet · checked 2026-09-03
Frequently asked questions
What does Vitamin B12 do?
A vitamin needed for nerve function and red blood cell formation; only found reliably in animal foods.
Does Vitamin B12 work?
ODS: treats deficiency, which is common in vegans, older adults and after stomach surgery.
How much vitamin b12 should I take?
RDA: 2.4 mcg per day. Any time; absorbed with or without food.
Is Vitamin B12 safe?
Vegans need a reliable source (supplement or fortified foods) — deficiency develops slowly and can be permanent if untreated. And the standing rule: tell your clinician everything you take — supplements interact with medicines.
Creatine
Studied doses: 3-5 g per day; loading protocols use about 20 g/day in 4 doses for 5-7 days.
Magnesium
RDA: men 400-420 mg, women 310-320 mg per day.
Vitamin D
RDA: 600 IU (15 mcg) to age 70, then 800 IU (20 mcg). UL 4000 IU.
Omega-3s (EPA/DHA)
No RDA for EPA/DHA; ALA: men 1.6 g, women 1.1 g per day. Many products supply 250-500 mg combined EPA+DHA per day.
Melatonin
Studied doses commonly 0.5-5 mg, taken 30-60 minutes before bed.
Iron
RDA: men 8 mg, women 19-50 18 mg, pregnancy 27 mg per day.
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