Vitamin B12
Methylcobalamin / cyanocobalamin / B12 shots · Foundation
Essential, cheap, and dramatic to fix when deficient — placebo-tier energy shots when you are not.
What the evidence says
Deficiency correction is textbook medicine with unambiguous benefit — and deficiency is genuinely common in vegans, long-term metformin users, and older adults (absorption, not intake, is usually the problem). In replete people, extra B12 — including the injection ritual — has repeatedly failed to beat placebo for energy.
What studies used
Supplement studies commonly use 500–1,000 mcg/day oral; deficiency treatment is a clinical decision. Published studies had not established a timing dependence.
Reported from published studies and product labelling — a record of what was used in research, not a recommendation. What is right for you is a conversation with a clinician.
Watch out for
- Long-term metformin use is associated with B12 deficiency; markedly reduced food intake from any cause may warrant individualized assessment
- High-dose oral treats most people effectively — passive diffusion absorbs a small fraction even without intrinsic factor — though injections remain the choice for severe neurologic disease or significant malabsorption
Evidence base
established literature
Large human evidence base: several phase 3 or 4 trial reports, plus multiple meta-analyses or systematic reviews.
This letter measures how much human research exists, not whether it works for you — the tier above (Strong) is the read on quality.
Research (12)
- Vitamin B12 and Plant-Predominant DietsAm J Lifestyle Med · 2022
- Vitamin B12Br Med Bull · 1956
- Vitamin B12 absorptionAm J Clin Nutr · 1958
- [VITAMIN B12]Dtsch Med Wochenschr · 1957
- VITAMIN B12 researchJ Am Med Assoc · 1953
- Vitamin B12 conferenceScience · 1953
- [Vitamin B12]An Inst Med Trop (Lisb) · 1957
- Vitamin B12Med Glas · 1953
- Vitamin B12Usp Sovrem Biol · 1950
- Vitamin B12Bull Chic Med Soc · 1949
- Vitamin B12S Afr Med J · 1950
- Vitamin B12Med Glas · 1950
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