Except it doesn't. A slow trickle of bad news has been coming through over the past couple years linking antioxidants with bad outcomes.
The first finding came from a large scale study conducted in England where half of 20,536 people considered high risk for heart disease took vitamin C,E, and beta-carotene supplements and half didn't. It found no difference at all in the rates of heart attack, other signs of cardiovascular disease, cancer or, indeed, hospitalization for any other cause.
Then a February 2007 study found that antioxidant supplements actually seemed to raise the risk of death in those who took them.
Yet another blow was dealt to the idea that antioxidants were helpful by the results of the Physicians Health Study II published in 2008. In this double blind, placebo controlled study of 14,641 male physicians taking Vitamin C or E or a placebo that lasted a decade, the conclusion was, " neither vitamin E nor vitamin C supplementation reduced the risk of major cardiovascular events." Not only that, but "...vitamin E was associated with an increased risk of hemorrhagic stroke."
However, there was some hope that supplementing with these vitamins might be of some use specifically in people with diabetes after studies showed that the beta cell was uniquely vulnerable to oxidative stress because it is poor in the production of antioxidant substances.
A paper published in 2000 that analyzed results of the large scale EPIC-Norfolk study seemed to suggest this was true. It found that the higher the plasma vitamin C level in the 6,458 people they studied, the lower their hba1c seemed to be.
But the question was whether the high level of vitamin C actually caused the lower blood sugar levels, or whether its presence was a marker for something else--for example a diet low in junk food.
A further analysis of EPIC Norfolk data published in 2004--after the early results were in suggesting he ineffectiveness of vitamin supplementation against heart disease, pointed to the latter explanation. The study title says it all: Occupational social class, educational level and area deprivation independently predict plasma ascorbic acid concentration: a cross-sectional population based study in the Norfolk cohort of the European Prospective Investigation into Cancer (EPIC-Norfolk) Shohaimi S, Bingham S, Welch A, et al. Eur J Clin Nutr, Mar 31 2004, e-pub.
Why drag this up again? Because two very intersting studies that came out this past year cast some light on WHY antioxidants may be bad for us.
The first is this study, available in full text:
Antioxidants prevent health-promoting effects of physical exercise in humans Michael Ristow et al. PNAS May 26, 2009 vol. 106 no. 21 8665-8670 doi: 10.1073/pnas.0903485106
The researchers in the PNAS study found that "Exercise increased parameters of insulin sensitivity (GIR and plasma adiponectin) only in the absence of antioxidants in both previously untrained (P < 0.001) and pretrained (P < 0.001) individuals."
Why? A rodent study conducted by Tony Tiganis and published in Cell Metabolism in October of 2009 [full text available online as of Oct 25, 2009] found that high doses of antioxidants may interfere with cellular processes in a way that increases insulin resistance.
Reactive Oxygen Species Enhance Insulin Sensitivity" Kim Loh et al. Cell Metabolism,Volume 10, Issue 4, 260-272, 7 October 2009, doi:10.1016/j.cmet.2009.08.009
To read a description of this study in layman's terms view:
Reuters: Antioxidants may increase diabetes risk
Since it is a mantra repeated throughout Diabetes research that ROS are strongly associated with the damage done by diabetes to our organs, after reading this we find ourselves scratching our heads.
We are told to exercise, but this research suggests exercise is only effective in reducing insulin resistance when antioxidants are not present and ROS are produced.
So what message should we take from this? My guess is that it suggests we should confine our intake of antioxidant vitamins to those that come bound up with foods that have long made up a normal part of the human diet. These foods contain very modest doses of antioxidants.
The studies finding problems with antioxidants all use large doses of supplemental vitamins. It is likely that the amount of Vitamin C in your veggies and the Vitamin E in your sunflower seeds is low enough to avoid overwhelming cellular processes like lab created vitamins do.
Rust is not the only example of oxidation in our environment. There is also flame. And when you are trying to burn nutrients, maybe a bit of oxidation is good for you.