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How Do Antioxidants Combat Oxidative Stress To Support Immune Health?
Linda May-Zhang, PhD


You may already know that antioxidants are good for health and that eating fruits and veggies full of antioxidants may help ward off inflammation, infections and illness by combating oxidative stress.

But what exactly is oxidative stress? How do antioxidants work? Let’s learn about the science behind antioxidants and ways you can keep healthy this season.

What is oxidative stress? How do antioxidants work?

Oxidative stress means the damage done within your body as a result of excessive free radicals. Free radicals are unstable molecules that are generated in your body from metabolism. The body’s ability to turn air and food into energy depends on free radicals. Free radicals also help cells communicate with each other and aid in fighting pathogens. So, free radicals aren’t necessarily a bad thing and are actually part of normal bodily processes. The body also has a way to prevent too much free radical production by using its own antioxidant defense systems. Antioxidants are molecules that stabilize free radicals so they no longer react. The body’s natural antioxidant defense systems help make sure free radicals do not get out of hand. Dietary antioxidants add another layer of protection.

Oxidative stress happens when there is an imbalance of free radical production and antioxidant defense systems. Excessive free radicals can cause a series of reactions in the body known as oxidation. The byproducts of these reactions can cause damage within the body, such as to DNA, protein and fatty tissues. As a result, chronic oxidative stress plays a major role in the development of many health conditions.

How does oxidative stress affect the immune system?

The immune system is especially sensitive to oxidative stress. Normally, infections trigger the body’s immune response, which serves to fight off the infection. Certain immune cells generate free radicals to fight off invading germs. These free radicals can damage healthy cells, leading to inflammation. Normally, after the infection is eliminated, inflammation goes away. If the body is under a state of oxidative stress, that can exaggerate the inflammatory response and trigger a “cytokine storm,” which in turn further exacerbates oxidative stress and creates a vicious cycle. Antioxidants keep the immune response in check so that it can effectively fend off illnesses without causing too much damage to the body.

What causes oxidative stress?

If our body is equipped with natural defense systems to keep free radicals in check, then what causes oxidative stress? Well, that is a million-dollar question that scientists are still trying to understand.

We know that free radical production is involved in many chronic health conditions and that people with low intakes of antioxidant rich foods have greater risk for developing these chronic conditions. Increased oxidative stress is also associated with aging. While research is still underway to understand what exactly causes increased oxidative stress, here are some risk factors that may increase oxidative stress in your body:

  • Diets high in fats, sugar and processed foods and low in fruits and vegetables
  • Smoking
  • Environmental factors such as radiation or pollution
  • Excessive alcohol consumption
  • Exposure to pesticides or industrial chemicals

4 antioxidants to combat oxidative stress

So how can you combat oxidative stress and keep your immune system in shape? Here are some antioxidants found naturally in food and also available in supplement formulas that can combat oxidative stress and help get your body back into balance.

Vitamin C

Also known as ascorbic acid, Vitamin C is a water-soluble antioxidant that supports many aspects of the immune system. Our bodies cannot make vitamin C, so we must get it from foods like bell peppers, broccoli, brussels sprouts, strawberries, and citrus fruits. People susceptible to vitamin C deficiency may benefit from taking vitamin C supplements. One study showed that vitamin C supplementation reduced the risk of catching a cold and cold duration in participants with low vitamin C [1].


Zinc is an antioxidant that is a powerful weapon for immunity. Low levels of zinc can lead to poor immune responses and antibody production. The body cannot make its own zinc, so we must get it from foods such as whole grains, meats, shellfish, dairy and beans. Certain groups of people are more likely to be susceptible to zinc deficiency than others, such as people who have digestive disorders or vegetarians, since meat products provide the majority of zinc in diets. Drinking alcohol also decreases the amount of zinc absorbed by the body. Research shows that oral zinc supplements may benefit people with low levels of zinc, and if taken soon after cold symptoms, may shorten the length of a cold [2].

Quercetin & Taxifolin

Quercetin is a natural antioxidant found in onions, kale, broccoli, apples and tea. Its unique biological properties offer many benefits to overall health as well as reducing inflammation and supporting immune function [3]. Taxifolin, also known as trans-dihydroquercetin, is an analogue of quercetin that is commonly found in milk thistle and onions, as well as many plants and fir trees. A more powerful antioxidant compared to quercetin [4], taxifolin is a very attractive natural compound to combat oxidative stress and support immune health.


Ergothioneine is a potent antioxidant found in mushrooms, beans, chicken, and pork liver. Although our bodies do not make ergothioneine, our body cells do express a transport protein known as the ergothioneine transporter, which makes scientists believe that this food-derived compound is critical to human health. While research on specific effects on immune function is still emerging [5], ergothioneine is demonstrated to combat oxidative stress and support other areas of health, including eye, cardiovascular and brain [6]. Recent research has also demonstrated that ergothioneine may support healthy aging. A study just published indicates that ergothioneine mitigates telomere shortening under oxidative stress conditions [7].

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[1] Johnston CS, Barkyoumb GM, Schumacher SS. Vitamin C Supplementation Slightly Improves Physical Activity Levels and Reduces Cold Incidence in Men with Marginal Vitamin C Status: A Randomized Controlled Trial. Nutrients 2014;6(7): 2572-2583.

[2] Rao G, Rowland K. Zinc for the common cold—not if, but when. J Fam Pract 2011; 60(11): 669-671.

[3] Li Y, et al. Quercetin, Inflammation and Immunity. Nutrients, 2016. 8(3): 167. DOI: 10.3390/nu8030167

[4] Sunil C, Xu B. An insight into the health-promoting effects of taxifolin (dihydroquercetin). Phytochemistry, 2019. 166: 112066.

[5] Halliwell B, et al. Ergothioneine – a diet‐derived antioxidant with therapeutic potential. FEBS Letters, 2018. 592(20).

[6] Yoshida S, et al. The Anti-Oxidant Ergothioneine Augments the Immunomodulatory Function of TLR Agonists by Direct Action on Macrophages. PLoS ONE, 2017: 12(1): e0169360.

[7] Samuel P, et al. Ergothioneine Mitigates Telomere Shortening under Oxidative Stress Conditions, Journal of Dietary Supplements, 2020; DOI: 10.1080/19390211.2020.1854919


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