“Vitamin B12 supplements boost energy when B12 status is already adequate.”
Extra B12 has not been shown to boost energy in people whose B12 is already adequate.
If your B12 is already adequate, taking more B12 will not give you more energy. Lasting tiredness is worth tracking down to its real cause.
If you are tired and fit one of the higher-risk groups, ask for a B12 blood test before buying a supplement. If you are not in a risk group, B12 is probably not the answer to your tiredness.
Talk to a healthcare professional if: you have been tired for weeks without a clear reason, or you also have numbness, pins and needles, balance problems, memory trouble or a sore tongue; or you are at higher risk of low B12 because you eat a vegan diet without fortified foods or supplements, have had stomach or weight-loss surgery, or take metformin, a proton pump inhibitor or an H2 blocker for stomach acid.
A review of 16 trials in people without a clear B12 deficiency found no benefit for thinking or mood, and the only trial of unexplained tiredness tested a B-vitamin mix and did not show a real benefit, because its placebo group started out with better scores. Confidence is limited because so few trials measured energy or fatigue directly.
Extra B12 has not been shown to boost energy in people whose B12 is already adequate. A 2021 review of 16 trials found only one that measured unexplained tiredness, and its one better score showed up only at the last check, in a group that started out worse than the placebo group, so it does not show a real benefit.
The 2021 review included 6,276 people who did not have an obvious B12 deficiency or advanced nerve disease. It found no effect of B12, alone or in a B-vitamin mix, on any area of thinking, and no overall effect on depression. The one fatigue trial tested a B-vitamin mix, not B12 alone, and reported better scores on one energy scale only at eight weeks; the placebo group had better scores at the start. The review was not limited to people with confirmed normal B12 levels, so it is indirect for this exact claim. This is different from true deficiency, where B12 does matter for energy: UK national guidance lists unexplained tiredness as a common symptom of B12 deficiency.
- Markun S, Gravestock I, Jäger L, Rosemann T, Pichierri G, Burgstaller JM. Effects of vitamin B12 supplementation on cognitive function, depressive symptoms, and fatigue: a systematic review, meta-analysis, and meta-regression. Nutrients. 2021;13(3):923. DOI: 10.3390/nu13030923. PMID: 33809274. PMCID: PMC8000524
- National Institute for Health and Care Excellence (NICE). Vitamin B12 deficiency in over 16s: diagnosis and management. NICE guideline NG239. Published 6 March 2024