Vitamin E and other antioxidants may increase the risk of developing lung cancer in high-risk populations such as smokers, according to a new study released Wednesday by the U.S. journal Science Translational Medicine.

Antioxidants are chemical compounds that prevent oxidation of other molecules, thus delaying some types of cell damage that could cause cancer. They include vitamins A, C and E, as well as some medications.

For a long time, antioxidants were thought to be potentially useful for preventing cancer, but recent clinical trials have suggested that antioxidants do not actually prevent smokers from getting lung cancer. However, the reason for this effect has been unclear.

Swedish researchers used two common antioxidants, vitamin E and a drug called NAcetyl Cysteine to examine the impact of antioxidant supplementation in mice, which already had small tumors in their lungs.

"What we found is that antioxidants caused a threefold increase in the number of tumors and also tumor aggressiveness," lead author Martin Bergo, professor of the University of Gothenburg, Sweden, told a press teleconference.