Why does vitamin E antioxidant therapy give mixed results in the clinic?

Antioxidant therapy has been on the radar as a means for combating and preventing disease for over 50 years. Just in the last couple of years, long term controlled clinical trials have finally come on board to assess the impact of antioxidant therapy by vitamin E supplementation on overall health and risk for various diseases. What is interesting about these trials is that most of them did not shown much benefit to vitamin E supplementation. In this article, we'll take a look at why clinical trials may not have sealed the deal on vitamin efficacy, and offer some insights into why there is likely more to this story than we can see so far.

The problem with trying to study vitamin E is that it doesn't serve a very specific function in the human body. So unlike a B or C vitamin, I can't just say "take vitamin E because otherwise you get ____." Vitamin E has a more general effect on your health by preventing free radical damage. As a result, clinicians in the field of vitamin E research have gotten some very confusing data.

Trials with human beings are fantastic because they are the "real thing." Real people are taking real pills. Not rats. Not cells in an incubator. The problem comes in when the doctors measure the outcome. When you can't just crack the person open to have a look, what do you measure?

It's easy to start with things like cancer, stroke, or heart disease. Perhaps not surprisingly, placebo-controlled clinical trials involving tens of thousands of patients have recently suggested that vitamin E does little prevent cancer or cardiovascular disease. The problem with clinical studies is that they measure big, systemic diseases that roll up many health and genetic factors. One little thing like vitamin E consumption is unlikely to show meaningful contribution to this outcome across a massive cross section of the population. Sorry, no magic pills (1).

Instead, more focused measurements of disease prevention by vitamin E antioxidant therapy have shown real benefits. The strategy is to look at particular populations with similar risks and measure similar outcomes.

Smaller, focused studies have demonstrated the benefits of antioxidant therapy

The smaller clinical trial strategy makes more sense than factoring in all the stresses that thousands of people have in their lives and seeing if vitamin E prevents them from getting cancer. There's too much noise to see a signal.

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References1. Steinhubl, SR. "Why have antioxidants failed in clinical trials?" Am J Cardiol. (2008) 101(10A), 14D-19D.