It goes against what many consider a given when it comes to living a healthy life, but at Vanderbilt, researchers said some supplements, especially in excess, could be bad for you.
"What we are worried about is mega-dosing," said Dr. Eric Skaar, "that's the idea that more is always better and that you should take as much as an individual nutrient as you can."
If you have a vitamin deficiency, researchers say you need to take your vitamins. But many supplements contain up to 5-times the recommended daily dose, and without a deficiency, taking them could do more harm than good.
Scientists looked at a deadly infection known as C. diff. It's currently the most common hospital-aquired disease in the U.S.
Patients can get it after taking high doses of antibiotics.
"When your good microbes go away from antibiotics, usually C. diff can then flourish," Skaar said, "it produces toxins that damage the cells in your body and you end up with a really nasty disease which is often fatal."
The study focused on how diet affects the infection too, by giving mice supplements (including zinc) both above and below recommended daily amounts.
Knowing that zinc is often associated with a healthy immune system, they expected the low-level mice to be more likely to get the disease. But in fact they found the opposite.
"If you had high levels of zinc they didn't need as much antibiotics to get infected," said Dr. Joseph Zackular. And their infections were much more severe than those with normal or below-average doses of the supplement.
They say it means too much of a good thing can be bad for your health. And if people who don't need them cut back on supplements, it could help their bodies and their wallets.
"It's a huge market," Dr. Skaar said, "theres a number of companies that make billions of dollars on supplements and they're not regulated by the FDA."
So what should you do?
They say think carefully about vitamins not recommended by your doctor. And there's something that's even more important: your eating habits.
"We're fortunate to be able to get most of our nutrients from food and vegetables and fruit and healthy grains. And if you can do that I don't think you have to worry about putting these extra things into your body," said Dr. Skaar.