A good example of a high-energy vitamin is vitamin B12, but there is no sufficient evidence to substantiate its effectiveness, notes WebMD. People taking a multivitamin do not need to take the supplement unless they are low on B12.
Vegans can take a vitamin B12 supplement because the vitamin is only found in animal foods, which they don't eat, explains WebMD. The right dosage of the supplement depends on the age of an individual, notes Healthline. People who experience vitamin B12 deficiency, including those suffering from celiac disease and HIV/AIDS, can take the supplement. Older adults can also take it to improve memory and enhance balance.