In short, it’s marketing and placebo. There are no additional benefits that those vitamins confer when you ingest an energy drink, provided you are not deficient.
B vitamins are associated with energy metabolism and because it’s an energy drink, it makes sense to have something that that is a cofactor in energy metabolism. That’s marketing.
These are water soluble vitamins, like others mentioned, they are not stored, although B12 is stored in the liver which indicates it’s importance for your body, so you can drink as many as you like without worrying about having too much.
Additionally, just for fun, vitamins of b group are produced by the body in some amounts by the bacteria and yeast in the intestines.
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