Talk about getting too much of a good thing. In recent years, health-conscious folks have been popping antioxidant vitamins like E, C, and beta-carotene in hopes of preventing a range of maladies, including Alzheimer’s disease, heart disease, and cancer. But a careful look at how one of these vitamins works in the petri dish has led to a disappointing discovery: Too much may actually trigger the production of LDL, or so-called bad cholesterol.

Scientists at New York University came across the surprising finding while studying the way polyunsaturated fatty acids suppress cholesterol production in liver cells. When they added vitamin E to the experiment, they found that it counteracted the good effects of the fatty acids, causing cholesterol production to increase. (Further tests of vitamin E in mice had a similar result.) The study only looked at E, but it stands to reason other antioxidants would have the same effect, says Edward A. Fisher, a professor of cardiology and cell biology who led the study.

So, should people stop megadosing on antioxidants? Certainly caution is in order, Fisher says. “The amounts we used were much higher than what you could get in your diet, but similar to those very high doses that some people take”—in some cases up to 1,000 percent of the RDA. “It’s a matter of finding the right balance,” Fisher adds. “If you don’t have high cholesterol, but you do have other health problems that supplements might help, you might decide they’re worth taking.”