Studies don't back this.
We reviewed the trials we hold for energy. The results for vitamin C and vitamin B12 were not strong enough to credit. In men with marginal vitamin C status, a small trial found a possible rise in physical activity, but the main difference was not clearly convincing. This is shortfall correction at most, not an energy boost for a replete adult. If your B12 is normal, extra B12 has no good evidence for boosting your energy. The legal energy wording describes avoiding a shortfall, not giving a replete person a lift.
See the evidence behind this answer in the complete report, including what was tested, the dose and preparation used, who took part, and funding information where available.
