Energy drink companies love to pump your body full of B vitamins. One popular “beverage” contains more than 8,000 percent of your daily value of B12, and 2,000 percent of your daily value of B6.

But here’s the thing: No one knows why. Not even experts on B vitamins.

B vitamins don’t boost your energy, says Catherine Champagne, Ph.D., R.D.N., director of dietary assessment and nutrition counseling at Louisiana State University’s Pennington Biomedical Research Center.

People who are deficient in B vitamins do feel tired, because the micronutrients help your body turn food into energy, says Marie Caudill, Ph.D., R.D., a professor of nutrition at Cornell University. Plus, being short on B vitamins causes anemia, which cuts off oxygen supply to your organs, causing fatigue.

However, deficiency is uncommon. If you eat a varied diet that includes meats, eggs, dairy, leafy greens, and whole grains, you’ll get plenty of B, says Champagne.

If you’re tired, it’s more likely that your fatigue is due to lack of sleep, stress, or overworking, says Champagne.

One caveat: People who adhere to a strict plant-only diet may not be getting enough B12, a vitamin that’s primarily found in animal foods.

But even if you are deficient, taking B vitamins won’t give you an immediate boost—it could take weeks or months for your energy levels to be restored, says Caudill.

What’s more, your body can only absorb so many B vitamins at a time, she says. So the majority of that 8,000 percent you’re ingesting? It gets pissed away.

The jolt you get from energy drinks comes from caffeine, and maybe sugar. But as for those B vitamins? It’s just marketing, says Champagne.