The research, carried out by researchers at Taipei Medical University Shuang-Ho Hospital, found that quercetin and ferulic acid, another plant-based compound found in many herbal remedies and diet supplements, seriously aggravated the effects of cancer in rats exposed to the substances.
The study, published in the Journal of Agricultural and Food Chemistry, examined severely diabetic laboratory rats with kidney cancer.
"In this study we report that quercetin aggravated, at least, if not directly caused, kidney cancer in rats," Kuan-Chou Chen, one of the authors of the study, said in a statement.
Quercetin is a naturally-occurring plant-based antioxidant that is found in particularly high levels in onions and black tea. It is also used in herbal supplements and energy beverages.
The news source reports that these findings raise concerns about the safety of some antioxidants that had been previously touted as "healthful."