Vitamin B12

Vitamin B12 is an essential cobalamin your body needs for nerve function, red-blood-cell production, and DNA synthesis. You get it from animal foods or supplementation, and deficiency is common in vegans, older adults, anyone on long-term metformin, and people with absorption issues. The injectable form, usually cyanocobalamin or hydroxocobalamin given intramuscularly, is the clinical standard for severe deficiency. But for most people, oral supplementation works just as well.

The wellness market sells B12 as an energy shot, and that framing is the problem. B12 is a deficiency story, not a performance story. Fix a deficiency and you feel better. Take it when you are already replete and nothing happens.

A deep evidence base that keeps arriving at the same answer, replete the deficient, do not oversell:

Start with a blood test. If your serum B12 is low or your homocysteine is elevated, correct it. If neither is true, you are done here.

For a confirmed deficiency, oral supplementation at 1000 micrograms daily works for most people, no injection needed. The meta-analyses consistently find no significant difference between oral and intramuscular routes. The exception is severe neurological symptoms or genuine absorption failure, pernicious anemia or post-gastric surgery, where the intramuscular route bypasses the gut entirely and is the right call.

If you are on metformin, monitor your B12 annually. Metformin depletes it over time, and supplementing to correct the gap is straightforward.

Vitamin B12 is one of the safest supplements that exists: