I have commented a few times on the issue of antioxidant supplements. While the theory that some diseases are caused by, or at least involve in some way, oxidative damage is reasonable, and there are lots of in vitro studies showing both the negative effects of free radicals and the antioxidant effects of many chemicals found in foods, the clinical data that one can prevent or treat specific diseases with antioxidant supplements is virtually nonexistent. The hype about antioxidants far exceeds the evidence (c.f. this article also) of any real value, and some evidence has developed showing that they have significant potential risks, including increasing the likelihood of some diseases and interfering with some kinds of medical therapy. So while the potential uses of antioxidants deserve further study, the automatic assumption that they are a good idea is increasingly contradicted by the evidence.
So it makes sense that the US Department of Agriculture has withdrawn a public database it had maintained since 2010 showing one possible measure of the antioxidant capacity of certain foods. The Oxygen Radicals Absorbance Capacity (ORAC) consisted of a variety of in vitro chemical measures for the potential antioxidant effects of certain foods. While this might be useful information in planning research, it was not appropriate as support for health claims, and yet this is how the data was routinely being misused. The USDA notice makes the following important points:
[There is] mounting evidence that the values indicating antioxidant capacity have no relevance to the effects of specific bioactive compounds, including polyphenols on human health.
There is no evidence that the beneficial effects of polyphenol-rich foods can be attributed to the antioxidant properties of these foods.
The data for antioxidant capacity of foods generated by in vitro (test-tube) methods cannot be extrapolated to in vivo (human) effects and the clinical trials to test benefits of dietary antioxidants have produced mixed results.
We know now that antioxidant molecules in food have a wide range of functions, many of which are unrelated to the ability to absorb free radicals.
All of these points simply acknowledge that the evidence from epidemiological studies that consuming certain foods is associated with lower risk of certain diseases may have nothing at all to do with the antioxidant hypothesis of the antioxidant capacity of chemicals in these foods. In fact, the evidence is growing that whatever the health benefits may be of eating such foods, it probably has little to do with their antioxidant activity.
However, the most important reason for taking down the database was not simple scientific accuracy but the deliberate misuse of the information to support unproven health claims. As the USDA announcement put it,
ORAC values are routinely misused by food and dietary supplement manufacturing companies to promote their products and by consumers to guide their food and dietary supplement choices.
Because uncritical acceptance of the notion that antioxidants are good for you is widespread, despite limited supporting data and some data against this hypothesis, supplement manufacturers have been using the USDA ORAC data to add legitimacy to unfounded marketing claims about the health value of their products. Undoubtedly, of course, manufacturers of supplements with purported antioxidant activity will find other ways to promote this as having health benefits despite the lack of string evidence to back up such claims. But it is encouraging to see the government acknowledge that such marketing strategies are not consistent with good science and to make an effort not to accidentally support them.