Skip to content

Fitness & Exercise

Do Antioxidants Curb an Exercise Benefit?

Study Shows Some Supplements May Affect the Impact of Exercise on Insulin Sensitivity
Font Size
WebMD Health News

May 11, 2009 -- Taking antioxidant supplements -- specifically, vitamin C and vitamin E pills -- may dull one of the benefits of exercise, new research shows.

The exercise benefit in question is better sensitivity to insulin, a hormone that regulates blood sugar.

The new study shows that when healthy men took vitamin C and vitamin E supplements daily during a month of exercise, their insulin sensitivity didn't improve, though other men following the same exercise plan and taking placebo pills did improve their insulin sensitivity.

The antioxidant supplements shut down the brief, normal spike in oxidation that follows exercise; that temporary bout of oxidation is needed to improve insulin sensitivity, according to the researchers, who included Michael Ristow, MD, chair of the department of human nutrition at Germany's University of Jena.

"The data confirm that exercise exerts positive effects on glucose metabolism, and thus may prevent type 2 diabetes," Ristow tells WebMD via email. He adds that the results also "suggest, for the first time, that these effects are mediated by free radicals or oxidative stress that are caused by exercise, and that antioxidants interfere with this health-promoting effect of exercise."

But Andrew Shao, PhD, vice president for scientific and regulatory affairs at the Council for Responsible Nutrition (a trade group for the supplements industry), says people shouldn't jump to conclusions based on one report.

Supplements and Exercise Study

Ristow's study included 40 healthy men in Germany. When the study started, half of the men were sedentary and half got regular exercise.

The researchers put all of the men on a monthlong exercise plan. For four weeks, the men got 85 minutes of exercise on five consecutive days per week.

During each session, the men wore heart rate monitors while they biked or ran for 20 minutes, did circuit training for 45 minutes, and spent a total of 20 minutes warming up and cooling down.

Throughout the study, half of the men took 500 milligrams of vitamin C twice daily and 400 international units of vitamin E daily. For comparison, the other men took placebo pills.

Lab tests done at the beginning and end of the study show that insulin sensitivity improved for all of the men taking the placebo pills -- but not for any of the men taking the antioxidants.

"Physical activity induced an increase in insulin sensitivity only in the absence of antioxidants," Ristow and colleagues write in the advance online edition of Proceedings of the National Academy of Sciences.

But don’t take this study to mean that if you’re active you should avoid antioxidant-rich fruits and vegetables.  Fruits and vegetables are still beneficial because they "contain hundreds of other substances and compounds that are health-promoting," Ristow tells WebMD.

Healthy Living Tools

Ditch Those Inches

Set goals, tally calorie intake, track workouts and more, all via WebMD’s free Food & Fitness Planner.

Get Started

Today on WebMD

pilates instructor
15 moves that get results.
woman stretching before exercise
How and when to do it.
couple working out
Moves you can do at home.
woman exercising
Strengthen your core with these moves.
man exercising
7 most effective exercises
Man looking at watch before workout
Overweight man sitting on park bench

Pollen counts, treatment tips, and more.

It's nothing to sneeze at.

Loading ...

Sending your email...

This feature is temporarily unavailable. Please try again later.


Now check your email account on your mobile phone to download your new app.

pilates instructor
jogger running among flowering plants
woman walking
Taylor Lautner