Many of you have written to me asking me to comment on a recent study that seemed to show that taking antioxidants prevents some of the health-promoting effects of physical exercise.
If you didn't read about the study, here's the New York Times article on it, which was one of the most e-mailed articles of the week.
Here's what happened: Michael Ristow, MD and his colleagues took 40 healthy young men, half of whom were known to be exercisers ("Previously trained") and half of whom were not ("Previously untrained"). Half of each group were randomly assigned to receive antioxidants-- 1000mg of vitamin C and 400 IUs of vitamin E--while the other half of each group received no supplementation.
All subjects then underwent a 4 week exercise training program.
What the researchers found was that taking the antioxidants seemed to prevent some of the benefits of exercise, regardless of whether the subjects were experienced exercisers or novices.
As you can imagine, this was disturbing.
But before you buy into the media headlines ("Vitamins Harmful!") let's look a little more closely at what happened.
We've known for a long time that exercise increases insulin sensitivity-- the ability of the cells to respond to insulin. When the cells are sensitive to insulin, they "open up their doors" and allow insulin to deposit sugar from the bloodstream into the cells where it can be used for energy. This is a good thing, and one of the many ways exercise benefits people. Insulin resistance- the opposite of insulin sensitivity- is when the cells kind of "lock their doors" and don't pay attention to insulin. When that happens, both sugar and insulin remain high in the bloodstream- a very bad situation and one which can lead to metabolic syndrome and diabetes. You don't want insulin resistance- you want insulin sensitivity.
The researchers in the study determined insulin sensitivity by using a measure called GIR (glucose infusion rate). They also measured a hormone called adiponectin, which helps make the body more sensitive to insulin.
Normally, when you exercise, both GIR and adiponectin would increase.
But for the folks taking the antioxidants, they did not.
In this study, GIR and adiponectin only increased in the group that did not take the antioxidants.
How and why might this be?
Dr. Ristow has a theory, and it goes something like this: When you exercise, you produce increased numbers of free radicals. (This is undisputed and well-known; exercisers consume a lot of oxygen, and free radicals come from oxygen.) But according to Dr. Ristow, these free radicals act something like a chicken pox vaccine- by introducing a small amount of a "poison" to the body, the body counters with defenses that have significant benefits to you. In other words, small amounts of a "bad" thing- like stress or free radicals- can actually stimulate defenses that wind up being protective and healthful. Ristow reasons that perhaps "disabling" these free radicals with antioxidants prevents the body from mounting its own defense operation.
Specifically, he suggests that perhaps the free radicals generated by exercise are required for the insulin-sensitizing capabilities of physical exercise in healthy humans. And that by "neutralizing" those radicals with antioxidants, we prevent that insulin-sensitizing response.
One reader of this newsletter- David Langford-- summed it up quite well: "Dr. Ristow believes that if you spare your body of the normal consequences for, say, a hard workout, then it won't respond as favorably, at least as far as glucose metabolism is concerned" he wrote me. "Ristow seems to be saying that if you stress your body to instruct it to respond, but then save it from the stressors, you've defeated something. You may improve your strength, your endurance, your health in many ways, but not your insulin resistance."
OK, maybe. But before you go throwing out your antioxidants, consider a few things:
- This is a four week study of healthy young men who, presumably, were not insulin resistant in the first place.
- The study didn't address the dozens of other benefits of exercise which presumably were unaffected by taking antioxidants (i.e. mood elevation, improved circulation, strengthening of the heart and bones and muscles)
- While this study appears to be very well done, let's not forget the hundreds- if not thousands- of other studies on the beneficial effects of antioxidants on protecting cells and DNA.
- The researchers admit that high intakes of fruits and vegetables- which have a ton of antioxidants in them- don't have any of the negative effects seen in this 4 week study.
- The study does not discount the value of vitamins, nutrients and phytochemicals that can be helpful for a variety of health conditions, prevention of disease and maintenance of health.
While I'd hardly say this study is definitive, I admit it raises some very interesting questions about antioxidants and exercise that will almost definitely stimulate further research. It'll be interesting to see the comments of some of my respected colleagues as they analyze the data. You can be sure I'll report those comments to you as soon as they come in.
Jonny Bowden, PhD, C.N.S. is a nationally known expert on weight loss, nutrition and health and is the author of several best-selling books.
