Open your eyes: It's the caffeine that's keeping you awake.

RODALE NEWS, EMMAUS, PA—Ever wonder what it is in those B-vitamin energy drinks and supplements that really pep you up?

The people who make them want you to think it’s the B vitamins. But ConsumerLab.com, an independent testing company, has released data showing that it's actually caffeine, the same stuff you can get in a cup of coffee, that provides the pep. And while the B vitamins have no meaningful effect on your energy level, some of them are present in such high amounts that they could put your risk at health. Except, in few cases, where the product makers have the nerve to give you less of those overhyped B's than the label promises.

THE DETAILS: What's the connection between B vitamins and energy? Tod Cooperman, MD, president of ConsumerLab.com explains that B vitamins are necessary to release energy from your food. But loading up on B's doesn't make them release more energy. “This is a misuse of the basic science of B vitamins by marketers," he says.

And though they're not getting you over the afternoon slump, the B vitamins can have an effect. “I doubt that people realize the enormous amount of vitamins they are taking with these shots," says Dr. Cooperman. "If you do use energy shots, be careful not to drink more than one or two a day, and don’t take other B vitamins. Otherwise, you run a risk of toxic effects.”

That said, some of the products don’t deliver on the B vitamins they promise. Among the B complex pill-type supplements tested, Kirkland Signature B-100 High Energy Complex contained only 17.9 percent of B12; while Isotonix Advanced B Complex had no detectable levels of B6, 53 percent of the labeled biotin amount, and 80 percent of the folic acid.

Two of the energy shot liquid supplements tested by the lab were low in folic acid: Stacker 2 6-Hour Power Shot provided a little more than 40 percent of the amount listed on the label; and 5 Hour Energy provided 75.5 percent.