Do Antioxidants Interfere with Fitness Gains?

Do Antioxidants Interfere with Fitness Gains?

(Last Updated On: April 5, 2019)

Do Antioxidants Interfere with Fitness Gains?

So often, we read about the benefits of antioxidants – molecules that fight free radicals. Antioxidants serve a useful purpose. Your cells are constantly churning out damaging free radicals as they replicate, divide and produce energy. After all, cells and the ATP-producing mitochondria inside, are always sucking up oxygen. Any time cells are exposed to oxygen, they can potentially form free radicals.

To counter the effects of the free radicals your cells naturally form, experts say to consume foods rich in antioxidants, like those in plant-based foods. Sounds like a plan, right?  Then information pops up suggesting antioxidants might interfere with some of the positive adaptations you get from working out. Is there any truth to this idea?

Exercise, Stress, and Free Radicals

Two of the most powerful antioxidant vitamins you get through diet are vitamins C and vitamin E. These vitamins are constantly at work donating electrons to cell-damaging free radicals to render them less destructive. You NEED this type of protection – but there are certain times when moderate stress may actually be favorable. That seems to be the case for exercise.

No doubt about it, the stress of exercise produces free radicals. While you’re exercising hard, mitochondria inside your cells ramp up their activity to keep your muscle cells supplied with energy – and they produce free radicals at the same time. No wonder! Your oxygen requirements go up by 10 times or more above your resting requirements when you exercise.  That’s a lot of oxygen exposure for your cells and lots of potential for free radicals to form.

Antioxidants Before a Workout?

You might think the best time to flood your body with antioxidants is just before a workout – to help counteract the damage. Makes sense, doesn’t it? But hold that thought. Science doesn’t support this idea. In fact, a controlled amount of oxidative stress may actually be beneficial during a workout and completely blocking free radical production may reduce the benefits you get from an exercise session.

You’ve heard the phrase, “What doesn’t kill you makes you stronger.” This may apply to exercise and antioxidant status as well. The idea is that exercise places your body under oxidative stress. In turn, your internal antioxidant defense system has to work harder and become stronger to deal with the added stress. The idea that controlled stress makes you stronger is called “hormesis.”

In response to the stress of exercise, your body upregulates antioxidant defenses and enzymes that repair DNA. These activities partially account for the health benefits you get from a workout. If you throw high levels of supplemental antioxidants into the system, your body’s natural antioxidant defense system doesn’t have to become stronger and more efficient. Just like a person who lays on the couch won’t get fit, your body’s natural defenses won’t get stronger unless they’re challenged.

Yes, it’s possible to overwhelm your cells ability to defend themselves by exercising excessively and not giving your body enough recovery time. However, reasonable quantities of exercise make your cellular defense systems stronger and more capable of protecting you. In turn, this may lower your risk for disease and even slow down the aging process.

What Does Science Show about Antioxidant Supplements?

Studies where endurance athletes took supplemental vitamin C and vitamin E did not show the supplements led to greater fitness gains. In fact, the athletes had lower levels of enzymes that increase mitochondrial production inside muscle cells. An increase in mitochondria is one of the beneficial adaptations to endurance exercise. With more mitochondria, cells can pump out more ATP. When you take antioxidant supplements, it seems to interfere with mitochondrial biogenesis.

Endurance exercise is one thing – but what about resistance training? In another study where participants supplemented with vitamin C and E and did 10 weeks of high-intensity resistance training, both groups made gains in muscle size, but there were differences in the amount of strength the participants developed. Those taking the antioxidant supplements gained less strength than the control group.

Antioxidants and Insulin Sensitivity

One way in which high levels of antioxidants interfere with the health benefits of exercise is the impact antioxidant vitamins have on insulin sensitivity. Studies show antioxidants, taken around the time of exercise, interfere with the insulin-sensitizing effects of exercise. One of the health benefits of exercise is it improves insulin sensitivity so your body can better regulate blood glucose. When you exercise, you produce more free radicals. Those free radicals, in turn, activate genes that enhance insulin sensitivity. If you don’t get some oxidative stress and free radical production, you don’t get this adaptation.

As Len Kravitz PhD., a researcher and exercise scientist at the University of New Mexico points out, exercise may be the best antioxidant there is. Your body has the ability to protect itself against moderate amounts of oxidative stress. Exercise is a controlled type of stress that turns on the body’s own antioxidant defense system.

Not that you should depend only on exercise to protect your cells against damage, it’s still important to eat fruits and vegetables, so you can benefit from the rich variety of healthful chemicals plant-based foods offer. What you should avoid is taking antioxidant supplements or timing your antioxidants to coincide with your workouts. You want some oxidative stress to be generated so your body can become better at combating it.

The Bottom Line

Avoid supplementing with antioxidants and get antioxidants naturally from plant-based foods. Don’t consume a large quantity of antioxidant-dense foods right before a workout. However, eating an apple or a bowl of vegetables before a workout shouldn’t be enough to interfere with exercise adaptations. Drinking 3 or 4 cups of concentrated green tea might.

A time an antioxidant supplement might be beneficial is if you’re exercising at a high altitude. Research shows vitamin E reduces free radical burden in athletes exercising at altitudes. If you’re heading towards the mountains to exercise, you might consider upping your vitamin E. Otherwise, enjoy a diet rich in fruits, vegetables, and whole foods and exercise in moderation. That’s the best way to lower your risk for disease and slow down the aging process.


References: “Antioxidants and Free Radicals”

Biogerontology. 2005;6(1):71-5.

NY Times Well. “Why Antioxidants Don’t Belong in Your Workout”

“Is Exercise the Best Antioxidant Supplement?” Len Kravitz, Ph.D.

American Journal of Clinical Nutrition, 72(suppl), 637S-646S.

Sports Med. 2011 Dec 1;41(12):1043-69. doi: 10.2165/11594400-000000000-00000.


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