Study: Antioxidant Vitamins May Reduce Benefits of Exercise

Posted By elissa on May 21, 2009 | 2 comments

There’s an interesting new study out, that questions the value of consuming antioxidant vitamins when exercising to improve health/wellness.  Here’s an excerpt from the NYT report:

Exercise is known to have many beneficial effects on health, including on the body’s sensitivity to insulin. “Get more exercise” is often among the first recommendations given by doctors to people at risk of diabetes.

But exercise makes the muscle cells metabolize glucose, by combining its carbon atoms with oxygen and extracting the energy that is released. In the process, some highly reactive oxygen molecules escape and make chemical attacks on anything in sight.

…The researchers, led by Dr. Michael Ristow, a nutritionist at the University of Jena in Germany, tested this proposition by having young men exercise, giving half of them moderate doses of vitamins C and E and measuring sensitivity to insulin as well as indicators of the body’s natural defenses to oxidative damage.

The Jena team found that in the group taking the vitamins there was no improvement in insulin sensitivity and almost no activation of the body’s natural defense mechanism against oxidative damage.

The reason, they suggest, is that the reactive oxygen compounds, inevitable byproducts of exercise, are a natural trigger for both of these responses. The vitamins, by efficiently destroying the reactive oxygen, short-circuit the body’s natural response to exercise.

The full study is here…it was short (4 weeks), and used fairly large – although not unusual – amounts of vitamin C (1,000mg) and E (400 IU), so it’s not known whether these results would be similar for smaller doses, and/or over a longer time frame.  In addition, it tells us nothing about the effects of other antioxidant nutrients often taken by exercisers (i.e., alpha lipoic acid, various phytonutrients and standardized herbal extracts).  Would these have similar effects?  No idea, although it seems like a reasonable hypothesis at this point.

So, free radicals aren’t purely evil after all! This is something I’ve touched on before, over on the forums I mod.  I often get asked to review people’s supplement stacks, and every once in a while, someone goes overboard on the antioxidant supps.  Here’s what I wrote in response to one such member, who was taking “3,000mg of C, 1,000mg of E, and 50,000IU of Beta Carotene daily”:

Time out for a moment to consider a point: supplementary antioxidants are all well and good, but should not be viewed as replacements for antioxidant compounds from dietary sources, which are varied and useful for a variety of health conditions. Hopefully your diet contains decent amounts of vegetables, fruits and other dietary sources of antioxidants. IMO, supplements should be considered within the context of your entire dietary intake, and by over-reliance on a few isolated compounds you could be missing out on other benefits…

Another thing to consider is that it might be possible to get too much of a good thing. Oxidative reactions and the generation of free-radicals are invariably portrayed as evil: but this is not strictly true…there are some very vital physiological reactions that depend on free radicals. You don’t want to be sucking down so many supplemental antioxidants, that you – in essence – throw the baby out with the bath water. Free radicals play an important physiologic role in intracellular redox reactions and the ability of natural killer cells to lyse target cells.

There is a tendency among many people trying to improve their health, to view things in “black/white” terms…if something is good, it’s 100% good – so the more, the better. Likewise, if something is bad, it’s pure evil, and must be avoided at all costs.

As you can see from the paras I quoted above, it’s not that simple.  “Good” things aren’t good in all circumstances (sometimes they can even be double-edged swords), and “bad” things aren’t uniformly bad.  Thus it is with free radicals…While it’s important to NOT veer to the opposite extreme and start avoiding vitamin and other antioxidant supps like the plague, it’s nonetheless important to question the practice of indiscriminately sucking down antioxidant supplements in the belief that free radicals are invariably harmful and should be suppressed at all costs.