What’s The Deal With Antioxidants?

We hear about antioxidants all the time. But what are they, and how important are they really for runners? Here's a crash course.

Photo: Getty Images

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Antioxidants are everywhere; teas, smoothie bowls and even chocolate bars tout their antioxidant content. But what exactly are these mysterious molecules, and do endurance athletes really need to reach for extra antioxidants at every opportunity?

What exactly is an antioxidant and a free radical anyway? 

Think of an antioxidant as a shield.  They are molecules that act as a protector against free radicals in the body.  Free radicals are compounds that can cause damage to cells in the body.  For runners, the predominant type of free radical produced in the body by exercise is called reactive oxygen species (ROS).  Our bodies actually make antioxidants to help keep free radicals in check, but antioxidant compounds can be found in fruits, vegetables, and other plant-based foods.  Examples of antioxidants include Vitamin E, Vitamin C, curcumin, Vitamin A and coenzyme Q10.

What about runners?

When free radicals outnumber the antioxidants in the body, it is considered a state of oxidative stress.  Oxidative stress, if left unchecked, can damage muscle tissue, increase muscle fatigue, and weaken the immune system.  Some studies on antioxidant supplementation have shown that muscle damage and delayed onset muscle soreness (DOMS) can be reduced post-training.  Others have shown decreased muscle fatigue and improved performance.

RELATED: The Lowdown On Antioxidant Supplements

What are the possible downsides?

While there are benefits, a growing body of research shows that antioxidant supplementation can hinder normal adaptive changes that occur post-exercise inside the muscle.  One of the goals of endurance training is to increase mitochondrial density so that more energy is available to working tissues when you are running.  In some cases, antioxidant supplementation has been shown to interrupt this process.  This is particularly evident in the case of Vitamin C+Vitamin E supplementation, where it has been shown that even modest doses of 1000mg of Vitamin C plus 400IU of Vitamin E can hamper mitochondrial adaptations.  In addition, excessive intake of antioxidants from supplementation can interrupt the body’s natural endogenous antioxidant processes, turning the antioxidant into a pro-oxidant, or a chemical that induces oxidative stress in the body.  Granted, this has been demonstrated at extremely high doses of Vitamin C (~1000mg/kg bw), but still raises a cause for caution.

The Bottom Line: The research is mixed on acute benefits of antioxidant supplementation, but it does point to having negative effects with long-term use of antioxidant supplements. Antioxidants from food sources can be beneficial to normal free radical balance in the body.  A more practical approach appears to be aiming for 5-9 servings of a wide variety of colors of fruits and vegetables to get the most out of your diet or sipping on your favorite green tea, but using those pills sparingly.

Mango Green Smoothie Bowl:

Servings: 1


  • 1 Banana (frozen)
  • 1 cup Frozen Mango
  • 1 cup Baby Spinach
  • 1/4 cup Vanilla Protein Powder
  • 3/4 cup Unsweetened Almond Milk
  • ½ Kiwi (peeled and sliced)
  • 1/2 cup Blueberries (fresh or frozen)
  • 1 tbsp Hemp Seeds


1) Blend banana, frozen mango, baby spinach, protein powder and almond milk until smooth.

2) Pour into a bowl and top with kiwi, blueberries, hemp seeds, and any other fun toppings you desire. Enjoy!

Do you have a question for our RDN? Send your trail-running-nutrition quandaries to kylee@flynutrition.org.

Kylee Van Horn is a licensed Sports Registered Dietitian and competitive trail runner.

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