Generally, antioxidants are considered to have health benefits. Such vitamins are thought to "mop up" harmful substances in the body called free radicals that are produced by natural metabolic processes. Previous studies have suggested that antioxidants prevent biochemical changes that cause cholesterol to deposit on artery walls, thereby blocking blood flow.

However, a new study published in the Journal of Clinical Investigation indicates that antioxidants may actually hamper a process that helps prevent the production of bad cholesterol.

Normally, liver cells break down a critical component of very low density lipoprotein (VLDL), which prevents it from being converted in the blood stream into low-density lipoprotein (LDL), commonly known as bad cholesterol.

However, in animal studies, lead researcher Dr Edward Fisher, from New York University School of Medicine, and his team found that antioxidants such as vitamin E hindered this process, and so the liver was able to destroy fewer of these VLDL components.

"Our study is the first to document this association between antioxidant vitamins and VLDL cholesterol," said Dr Fisher. "It does appear that antioxidant vitamins may be potentially harmful for the heart based on their ability to increase the secretion of VLDL in the liver cells and in the mice that we studied."

However, he said that further research is needed to confirm the findings and that "until more data becomes available, we can't make any recommendations about whether people should not use these vitamins."

Indeed, he added that antioxidants may still have beneficial effects and pointed out evidence from other animal studies suggesting that antioxidants may protect the arteries from atherosclerosis (artery disease) and the pancreas and other organs from damage caused by diabetes.