Antioxidants overrated?

photo: Andrea Pokrzywinski via Flickr

If you get your nutrition factoids from food labels, you probably think antioxidants are miraculous cure-alls, and the more the better.  Or you might believe they kill germs, as a recent sample of consumers thought.  But don’t feel bad; even food scientists and health professionals aren’t quite sure if they’re all that useful.  Dr. Carl Keen, professor of nutrition at UC Davis, thinks the term antioxidant should be banished from food labels.  In his opinion, touting the antioxidant content of a food, based on what those antioxidants do in a test tube experiment, is meaningless.  There isn’t enough data about whether antioxidants are absorbed into cells, where they might provide health benefits.  Or not.

Another group of researchers takes Dr. Keen one step further in a new review: Antioxidants in Food: Mere Myth or Magic Medicine.  The behavior of antioxidants in the human body depends on dozens of variables that can’t be replicated in a test tube, and are impossible to control or predict at any one time.  More confusing: some antioxidants actually become pro-oxidants at certain higher concentrations.  The authors also argue that studies using one or two isolated “antioxidants” to show some health benefit miss the fact that diseases are complicated and have many contributing factors.  The likelihood of one or two magical antioxidants curing anything is remote at best.  Not to mention, typical short term studies are no where near long enough to prove any long range health benefit.  They conclude:

… a permanent intake of [high] dosages of isolated antioxidants should not be recommended to healthy consumers… It is high time to readjust the biased views on antioxidants, and to base medical and “health” statements on sound data.

A very recent study would seem to agree.  The data indicates that excess doses of beta-carotene, the pigment found in carrots, sweet potatoes and dark green, could end up blocking vitamin A activity.  The researchers believe metabolites of excess beta-carotene intake act like anti-vitamin-A.  Meaning it could interfere with all the essential activities of vitamin A in skin health, vision, immunity and numerous other roles.  This finding provides an explanation for a surprising study outcome years ago, when smokers who were given huge doses of beta-carotene supplements, which were assumed to be protective, actually ended up with more lung cancer than non-supplemented smokers.

But lest you are feeling somewhat anti-antioxidant after all this, consider a recent study of blueberries.  A small group of trained athletes were split into a control group and a blueberry-eating group.  Those subjects had to eat roughly 1/2 lb of blueberries every single day for 6 weeks.  That’s a lot of blueberries (NOTE: the study was funded by blueberry producer trade groups).  On test day, they had to eat another 3/4 lb, before spending 2-1/2 hours on a treadmill.  Before and after the treadmill session, all the subjects had blood drawn and a muscle biopsy (ugh).  Numerous tests were done to measure stress and inflammation markers.  The assumption was that the blueberry group, with a high intake of anthocyanins for 6 weeks, would show higher antioxidant capacity and less inflammation.  The blueberry group showed an interesting, if unexpected, effect: levels of natural killer cells, which are part of the immune system, were almost doubled.  A few of the other stress/inflammation markers were improved in the blueberry group, although not all of those measured.  In other words, the effect of blueberries seemed to be very specific to certain markers, with the increase in natural killer cells being the most interesting.

The one major drawback: eating 1/2 lb of blueberries every single day could lead to blueberry burn out.  Not to mention, it would be expensive.  The study does hint that blueberries could have some beneficial effect, but would it be noticeable for the average sedentary person who eats 1/2 cup every now and then?  Who knows.  But at least it was a study done on actual humans, measuring actual biological markers, not some hypothetical test tube experiment.  Antioxidants may have some benefit after all, just not as miracle cure-alls.
