Researchers found vitamins including E, C and beta carotene stop the liver breaking down an early form of bad cholesterol. Most research tends to suggest that supplementation with antioxidant vitamins, although not beneficial, does not lead to undue harm. These antioxidants are typically thought to be beneficial because they attack free radicals, produced when the body fights infection, which inflict damage on the body's tissues.
However, researchers found that these antioxidants actually hampered the body's fight against damaging cholesterol. Normally, liver cells break down a key protein in harmful lipoproteins such as VLDL (very low density lipoprotein), which means they cannot be converted into a form of LDL that can enter the bloodstream. The researchers found vitamin E, C and beta carotene prevented this process taking place in liver cells. Further tests in mice and rat livers showed vitamin E prevented this "breakdown" process taking place, meaning the liver destroyed fewer lipoproteins.
Although there is considerable evidence for the benefits of antioxidants, the potential for unintended outcomes of oxidant therapy should serve as a warning against proceeding with such treatment in the absence of clinical-trial evidence of benefit and safety. Does this mean I will stop taking vitamin E? No, but I believe this study can serve as a warning that just because a vitamin, mineral or nutrient may be helpful in some circumstances, it may cause problems in others.
The major problem results when we consume concentrated vitamin supplements in high "drug-like" doses. While this may be useful in certain circumstances, it clearly has the potential to cause problems. That is why in my journey to understand health and nutrition I have reached the conclusion that it is nearly always preferrable to obtain supplements from healthy whole unprocessed foods as all of the supporting nutrients are present in the proper ratios. Bottom line: get most of your nutrition from food--not supplements.
Journal Clinical Investigation May 2004;113(9):1277-87.