The short version
- B vitamins act as co-enzymes in the reactions that release energy from food, which makes them required for the process rather than capable of driving it faster.
- Roughly 6% of adults aged 60 and over in large US and UK surveys had plasma vitamin B12 below 148 pmol/L, and closer to 20% had marginal status of 148 to 221 pmol/L.
- In the Diabetes Prevention Program Outcomes Study, low or borderline-low B12 was found in 19.1% of metformin users versus 9.5% on placebo at five years, with an odds ratio of 1.13 per year of metformin use.
- Across 40 studies of vegetarian diets, B12 deficiency prevalence in adults ranged from 0 to 86.5% and was consistently higher in vegans than in other vegetarians.
- Pooling 11 randomised trials with cognitive data on 22,000 people, B vitamins lowered homocysteine by 28% but produced no significant change in cognitive function, with a z-score difference of 0.00 (95% CI -0.05 to 0.06).
Turn over almost any B-complex and the same word is on the front: energy. It is not quite a lie. It is a technical term borrowed from biochemistry and dropped into a sentence where it means something else entirely, and the gap between the two meanings is where most of the money in this category is made.
The honest version is short. B vitamins are required for the reactions that release energy from food. Required is not the same as rate-setting. If you are not short of them, adding more does nothing you will notice.
What "energy metabolism" means on a label
The B group is eight water-soluble vitamins that work as co-enzymes — helper molecules an enzyme must have present before it can work at all. Kennedy's 2016 review describes them acting "in a vast array of catabolic and anabolic enzymatic reactions", covering energy production, DNA synthesis and repair, methylation, and the manufacture of neurochemicals.
Read that as a job description, not a dose-response curve. A co-enzyme is a component the machine needs in place; once the position is filled, filling it again does not raise output. Which is why "supports energy metabolism" is both true and almost useless as a reason to buy. It describes what the vitamin does in a body that already has enough, and most bodies do.
Kennedy himself does not land where we do, and you should hear that from us rather than find it later. His review argues that a significant proportion of people in developed countries are deficient or insufficient in one or more of these vitamins, and that supplementing the whole group at doses well above government recommendations would be rational. We think that is a larger leap than the trial evidence supports. It is a live disagreement, not a settled question we have won.
What being short of one actually looks like
Deficiency is not a mood. It is a measured blood level, and the one that matters most in practice is B12.
Allen's review of large surveys in the United States and the United Kingdom found that roughly 6% of people aged 60 and over were vitamin B12 deficient, defined as plasma B12 below 148 pmol/L, with prevalence rising as age rises. Closer to 20% had marginal status — 148 to 221 pmol/L — in later life. In younger adults the main cause is straightforwardly inadequate intake, driven by low consumption of animal-source foods. In older adults the dominant cause changes: food-bound cobalamin malabsorption, at least partly due to gastric atrophy. Which is the bit people miss — an older adult can eat plenty of B12 and still absorb very little of it.
Two more groups worth testing
People taking metformin. The Diabetes Prevention Program Outcomes Study followed 1,073 people assigned to metformin and 1,082 to placebo. At five years, low B12 — 203 pg/mL or below — was present in 4.3% of the metformin group versus 2.3% on placebo. Including borderline-low levels, at 298 pg/mL or below, widened the gap considerably: 19.1% versus 9.5% at five years, and 20.3% versus 15.6% at thirteen. Each additional year of use carried an odds ratio for B12 deficiency of 1.13 (95% CI 1.06 to 1.20). The authors' recommendation was not that anyone stop metformin, but that routine B12 testing in people taking it should be considered.
To be completely clear, because this is exactly the paragraph people misread: nothing here is a reason to change or stop a prescribed medication. It is a reason to ask whoever prescribed it whether your B12 has been checked.
Vegans, and vegetarians to a lesser degree. Dietary B12 comes overwhelmingly from animal-source foods, so intake is the whole game. Pawlak and colleagues reviewed 40 studies reporting serum B12 across vegetarian diets. Deficiency prevalence among adults and elderly individuals ranged from 0 to 86.5% between studies — a spread that shows how much depends on the exact diet — and was consistently higher in vegans. Their conclusion: vegans not taking a B12 supplement are at especially high risk, and vegetarians of any kind should be screened.
What happens when you top up a level that was already fine
This is the question the label is quietly answering yes to, and the largest test of it points the other way. Clarke and colleagues pooled 11 randomised trials with cognitive data on 22,000 participants, comparing B vitamins against placebo over years rather than weeks. The vitamins worked in the narrow biochemical sense: homocysteine fell by 28% in the four cognitive-domain trials and 26% in the seven global-cognition trials. The chemistry moved. The people did not. There was no significant effect on memory, processing speed, executive function or global cognition — a z-score difference of 0.00, 95% CI -0.05 to 0.06.
Be precise about what that shows. Those were cognition trials, not fatigue trials, largely in older participants, at doses chosen to shift homocysteine — nobody has run a 22,000-person trial on whether B vitamins make replete adults feel less tired, and we will not imply otherwise. But a confidence interval that tight around zero, in the biggest B-vitamin trial programme ever assembled, is the best evidence available on adding B vitamins to somebody who did not need them. Measurably: the chemistry. Noticeably: nothing.
The bit of our own label we would rather you heard from us
Our IGNITE energy powder contains thiamin, riboflavin, niacin, B6, folate, B12 and pantothenic acid. It also contains caffeine and L-theanine.
If you drink it and feel something in the next half hour, that is the caffeine. It is not the B12. The B vitamins are in there because they belong in a formula built around energy metabolism and because they are cheap cover for anyone short — not because they are what you are feeling. Any brand that lets you believe otherwise is trading on a word, us included if we get sloppy.
There is one exception to pointless but harmless, and it is worth knowing because B6 sits in almost every B-complex on the shelf. A 2023 systematic review of twenty studies concluded that the evidence supports a neurotoxic role for B6 at high levels: raised B6, usually from supplements rather than food, is associated with a sensory neuropathy — numbness and tingling — which people report improving once they stop taking it. The same review found no proven harm at permitted daily doses, including from ordinary multivitamins. So this is not an argument against the amount on a normal label. It is an argument against megadosing a vitamin you were never short of, which is exactly what "more must be better" talks people into.
What we'd actually tell you
If any of the three groups above describes you, the useful move is a B12 level, not a B-complex. One cheap blood test turns a guess into a number. If it comes back low or borderline, address that specific thing at a matching dose and retest.
If you are not in one of those groups and you are tired, a B-complex is the wrong tool and an expensive way to discover it. Tiredness that is new, persistent and not explained by how you are sleeping deserves a proper look — thyroid, iron stores, sleep quality, mood, and yes, B12. Those are answerable questions. None get answered by a tub.
Good questions
Do B vitamins actually give you energy?
No, not unless you were short of one to begin with. B vitamins are co-enzymes in the reactions that release energy from food, which means they have to be present for the process to run. Once the requirement is met, adding more does not raise output. A stimulant changes how you feel; a co-enzyme fills a slot that was probably already full.
Will a B-complex help if I'm tired all the time?
Probably not, and it is an expensive way to find out. Persistent tiredness that is not explained by your sleep is worth investigating properly rather than supplementing at. Thyroid function, iron stores, sleep quality, mood and B12 are all measurable in a single morning. If a level comes back low, treat that specific thing at a matching dose and retest.
How do I know if I'm low in B12?
A blood test, not a symptom checklist. Deficiency is defined by a measured plasma level rather than by how you feel, and marginal status sits in a band just above the deficiency cut-off. In large US and UK surveys about 6% of people aged 60 and over were below 148 pmol/L, and roughly 20% were in the marginal 148 to 221 pmol/L range.
Does metformin cause B12 deficiency?
Long-term use is associated with it. In the Diabetes Prevention Program Outcomes Study, low or borderline-low B12 was present in 19.1% of metformin users versus 9.5% on placebo at five years, and each year of use carried an odds ratio of 1.13. The study authors recommended considering routine B12 testing, not stopping the drug. Never change a prescribed medication over a blog article.
Do vegans need a B12 supplement?
Yes, and this is the clearest case in the whole category. Dietary B12 comes overwhelmingly from animal-source foods, so intake is the limiting factor. A review of 40 studies found deficiency consistently more common in vegans than in other vegetarians, and concluded that vegans not taking a supplement are at especially high risk. Screening is worth asking for either way.
Is there any harm in taking a B-complex I don't need?
The likeliest cost is financial rather than physical, but B6 is a real exception worth knowing about. A 2023 systematic review concluded that high B6 levels, usually from supplements, can cause a sensory neuropathy that improves once you stop, while finding no proven harm at permitted label doses. Otherwise expect what the largest trial programme found: 11 trials, 22,000 people, homocysteine down 28%, cognition unchanged.
Sources
- Kennedy DO. B Vitamins and the Brain: Mechanisms, Dose and Efficacy — A Review. Nutrients, 2016. View study
- Allen LH. How common is vitamin B-12 deficiency? Am J Clin Nutr, 2009. View study
- Aroda VR, et al. Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab, 2016. View study
- Pawlak R, Lester SE, Babatunde T. The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: a review of literature. Eur J Clin Nutr, 2014. View study
- Clarke R, et al. Effects of homocysteine lowering with B vitamins on cognitive aging: meta-analysis of 11 trials with cognitive data on 22,000 individuals. Am J Clin Nutr, 2014. View study
- Muhamad R, Akrivaki A, Papagiannopoulou G, Zavridis P, Zis P. The Role of Vitamin B6 in Peripheral Neuropathy: A Systematic Review. Nutrients, 2023. View study
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
