Investigators at Vanderbilt University Medical Center in Nashville suggest the earlier studies all had a fundamental flaw -- all of the studies were designed in a way that never assessed the ability of the dose of vitamin E tested to reduce oxidant stress.

Dr. Jack Roberts and Dr. Jason Morrow determined it took 16 weeks at a very high dose of vitamin E -- 3200 IU/day -- to suppress oxidative stress in individuals at risk for cardiovascular disease.

The researchers then administered varying doses -- 0, 100, 200, 400, 800, 1600, and 3200 IU/day -- over the 16-week period to find the minimum effective dose. They found it was necessary to give at least 1600 IU per day to cause a significant reduction in oxidative stress -- twice the amount used in some clinical trials.

However, even with a massive dose of vitamin E the researchers observed a 50 percent reduction in F2- isoprostanes -- a measure of oxidative stress status, the journal Free Radical Biology and Medicine reported.

"In my opinion, vitamin E is not the spiffy antioxidant everybody thinks it is -- it’s a pretty poor antioxidant," Roberts said in a statement.