Oxidative Stress vs. Antioxidants

Quick Answer: Oxidative stress occurs when harmful free radicals outnumber your body's protective antioxidants — damaging cells, driving inflammation, and contributing to chronic disease. Your body's primary defense is glutathione peroxidase, an enzyme that requires both selenium and NAC to function. Supporting these two nutrients together is one of the most direct ways to strengthen your antioxidant defenses.

Key Takeaways:

✓ Oxidative stress occurs when your body can't neutralize harmful free radicals
✓ Your immune system produces free radicals to fight infections, but excess ROS can damage your own cells
✓ Glutathione peroxidases are your body's master antioxidant enzymes
✓ Selenium and NAC work together synergistically to support this critical defense system
✓ SelNAC provides both nutrients in optimal, bioavailable forms

 

Ever wonder why you feel exhausted after fighting off a cold, or why inflammation seems to linger? The answer might be oxidative stress. 

What is Oxidative Stress?

As your immune system works hard to disarm and kill off invading pathogens, oxidative stress can occur. Oxidative stress is when there is an imbalance between harmful free radicals and protective antioxidants, or when your body is unable to cope with or get rid of the sudden or prolonged increase of reactive oxygen species (ROS) – unstable molecules your immune system produces^1,2,3.

What makes ROS damaging is their presence of free radicals–unstable molecules that steal electrons from your DNA, fats, and proteins⁴. As a result, chronic oxidative stress can lead to cell damage or death, and inflammation, and is often also associated with age-related diseases and cancers^1,2,4. 

Why Does Oxidative Stress Happen?

While excessive ROS are harmful to your body’s cells, it can be weaponized against pathogenic microbes (e.g., bacteria, viruses, fungi). One type of leukocyte (white blood cell) called the macrophage, can phagocytize or engulf pathogens⁵. Once a macrophage engulfs a pathogen, it traps it in an intracellular sac called the phagolysosome, where digestive enzymes, antimicrobial peptides and ROS degrade it^5,6. 

Oxidative stress accumulates from more than just infections. Environmental toxins, intense exercise, mental stress, poor diet, and normal aging all contribute to free radical damage - meaning your body's antioxidant systems are working constantly, not just when you're sick.

How Do Pathogens Fight Back Against Oxidative Stress?

Unfortunately, while our bodies have figured out a way to use oxidative stress against invaders, so have the pathogens. If our body's own ROS byproducts, which are already harmful during ongoing infections, aren't trouble enough, viruses can crank out even more ROS to distract the immune system⁷. 

Studies have also shown that certain viruses can counteract ROS attacks by decomposing certain ROS by converting them back to oxygen and water⁷. Furthermore, these pathogens can hijack host cells to promote further ROS production8. 

What Are Antioxidants and How Do They Work?

So what are antioxidants? 

Antioxidants are compounds that help to protect the body’s cells from ROS damage by donating one of their own electrons, or teaming up with enzymes to transfer electrons to neutralize free radicals^3,9. They can be found in some of your favourite foods, such as blueberries and elderberries as anthocyanins, or flavanols as found in cocoa¹⁰. Your body also naturally produces powerful antioxidants like glutathione peroxidases, which require minerals like selenium and amino acids like N-acetyl-L-cysteine (NAC) to effectively detoxify ROS^3,10,11. 

Why This Matters for Your Daily Health

Oxidative stress accumulates from more than just infections. 

Environmental toxins, intense exercise, mental stress, poor diet, and normal aging all contribute to free radical damage in your cells. Therefore, your body's antioxidant systems are constantly required to deal with oxidative stress, not just when you are sick. 

Glutathione Peroxidase: Your Master Antioxidant 

Glutathione peroxidases, referred to as the “master antioxidants”, exist in almost every cell in your body. These enzymes are one of the most powerful first-line antioxidant defense systems. They neutralize hydrogen peroxide (H₂O₂)^12,13, which is a chemical substrate for the production of the most potent damaging free radicals your body encounters. 

However, in order for them to work effectively, glutathione peroxidase require two key nutrients^12,13,14:

1. Selenium - Is built into the enzyme itself as selenocysteine. Selenium "activates" their ability to neutralize free radicals
2. Cysteine (from NAC) - Provides the raw materials your cells need to produce glutathione, which is utilized by glutathione peroxidases to neutralize free radicals 

Without adequate selenium, these enzymes can't function. Without sufficient cysteine, your body can't produce enough glutathione for optimal enzyme function. Therefore, both are essential.

SelNAC: Powering Your Antioxidant Defense 

Selenium and NAC work synergistically. NAC possesses direct antioxidant activities, but also indirect activities by providing the cysteine your body needs to produce glutathione. Selenium ensures glutathione peroxidase enzymes can use that glutathione effectively.

While cysteine can be obtained directly from diet or supplements, NAC has significantly higher bioavailability than cysteine alone. This is because free cysteine is rapidly oxidized in the digestive tract before it can be absorbed, whereas NAC is more stable and is efficiently converted to cysteine once inside the body¹⁵. 

NAC alone produces glutathione, but without selenium, the enzymes can't use it efficiently. Therefore, Selenium and NAC together create a complete antioxidant support system.

SelNAC is a supplement that combines selenium (a glutathione peroxidase cofactor) and NAC (a cysteine donor) to synergistically support the body’s ability to produce and optimize glutathione peroxidase functions, one of your body’s first line defense mechanisms against oxidative stress. 

SelNAC combines:

• 200 mcg of selenium from highly bioavailable selenium-enriched yeast
• 300 mg of NAC — a stable, efficiently absorbed form of cysteine

Together, these two nutrients address both sides of the glutathione peroxidase equation: the enzyme activation and the substrate supply.

Frequently Asked Questions

What causes oxidative stress in everyday life? Oxidative stress isn't just caused by illness. Intense exercise, environmental toxins, chronic mental stress, poor nutrition, and normal aging all generate free radicals that your antioxidant systems must continuously neutralize. Supporting those systems proactively — not just during illness — is what matters most.

What is the difference between selenium and NAC? Selenium and NAC work at different points in the same antioxidant pathway. Selenium is structurally built into glutathione peroxidase enzymes and activates their ability to neutralize free radicals. NAC provides cysteine, the building block your cells use to produce glutathione — the molecule the enzyme needs to do its job. They're complementary, not interchangeable.

Why not just take a general antioxidant supplement? General antioxidants like vitamin C and E provide useful support, but they work differently than glutathione peroxidases. Supporting your body's own enzymatic antioxidant systems — which are active in nearly every cell — addresses oxidative stress at a more fundamental level than dietary antioxidants alone.

Is SelNAC safe to take daily? SelNAC is formulated with selenium at 200 mcg — within established safe supplementation ranges — and NAC at 300 mg, a well-researched dose. As with any supplement, consult your healthcare professional before starting, particularly if you have existing health conditions or take medications.

---

What To Do Next:

1. Assess your current diet for antioxidant-rich foods — berries, leafy greens, nuts, and seeds are good starting points
2. Consider whether your selenium intake is adequate — deficiency is common, particularly in regions with selenium-depleted soil
3. Learn more about SelNAC and how selenium and NAC work together
4. Consult your healthcare provider if you have questions about oxidative stress, chronic inflammation, or supplement use
5. Shop SelNAC at immunoceutica.ca 

Disclaimer: This article is for informational purposes only and is not medical advice. Always consult your healthcare professional before starting any supplement, especially if you have medical conditions or take medications.

References 

1. Marrocco, I., Altieri, F., & Peluso, I. (2017). Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans. Oxidative Medicine and Cellular Longevity, 2017(1), 6501046. https://doi.org/10.1155/2017/6501046
2. Tan, B. L., Norhaizan, M. E., Liew, W.-P.-P., & Sulaiman Rahman, H. (2018). Antioxidant and Oxidative Stress: A Mutual Interplay in Age-Related Diseases. Frontiers in Pharmacology, 9, 1162. https://doi.org/10.3389/fphar.2018.01162
3. Gulcin, İ. (2025). Antioxidants: A comprehensive review. Archives of Toxicology, 99(5), 1893–1997. https://doi.org/10.1007/s00204-025-03997-2
4. Yang, Z., Min, Z., & Yu, B. (2020). Reactive oxygen species and immune regulation. International Reviews of Immunology, 39(6), 292–298. https://doi.org/10.1080/08830185.2020.1768251
5. Herb, M., & Schramm, M. (2021). Functions of ROS in Macrophages and Antimicrobial Immunity. Antioxidants, 10(2), 313. https://doi.org/10.3390/antiox10020313
6. Canton, M., Sánchez-Rodríguez, R., Spera, I., Venegas, F. C., Favia, M., Viola, A., & Castegna, A. (2021). Reactive Oxygen Species in Macrophages: Sources and Targets. Frontiers in Immunology, 12, 734229. https://doi.org/10.3389/fimmu.2021.734229
7. Wenzhong, L., & Hualan, L. (2021). COVID-19: Captures iron and generates reactive oxygen species to damage the human immune system. Autoimmunity, 54(4), 213–224. https://doi.org/10.1080/08916934.2021.1913581
8. Xie, J., Yuan, C., Yang, S., Ma, Z., Li, W., Mao, L., Jiao, P., & Liu, W. (2024). The role of reactive oxygen species in severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) infection-induced cell death. Cellular & Molecular Biology Letters, 29(1), 138. https://doi.org/10.1186/s11658-024-00659-6
9. Sikder, M. M., Li, X., Akumwami, S., & Labony, S. A. (2025). Reactive Oxygen Species: Role in Pathophysiology, and Mechanism of Endogenous and Dietary Antioxidants during Oxidative Stress. Chonnam Medical Journal, 61(1), 32. https://doi.org/10.4068/cmj.2025.61.1.32
10. Harvard Health Publishing. (2019, January 31). Understanding antioxidants. https://www.health.harvard.edu/staying-healthy/understanding-antioxidants
11. Aldini, G., Altomare, A., Baron, G., Vistoli, G., Carini, M., Borsani, L., & Sergio, F. (2018). N-Acetylcysteine as an antioxidant and disulphide breaking agent: The reasons why. Free Radical Research, 52(7), 751–762. https://doi.org/10.1080/10715762.2018.1468564
12. Zoidis, E., Seremelis, I., Kontopoulos, N., & Danezis, G. (2018). Selenium-Dependent Antioxidant Enzymes: Actions and Properties of Selenoproteins. Antioxidants, 7(5), 66. https://doi.org/10.3390/antiox7050066
13. Jomova, K., Alomar, S. Y., Alwasel, S. H., Nepovimova, E., Kuca, K., & Valko, M. (2024). Several lines of antioxidant defense against oxidative stress: Antioxidant enzymes, nanomaterials with multiple enzyme-mimicking activities, and low-molecular-weight antioxidants. Archives of Toxicology, 98(5), 1323–1367. https://doi.org/10.1007/s00204-024-03696-4
14. Lee, J.-G., Jang, J.-Y., & Baik, S.-M. (2025). Selenium as an Antioxidant: Roles and Clinical Applications in Critically Ill and Trauma Patients: A Narrative Review. Antioxidants, 14(3), 294. https://doi.org/10.3390/antiox14030294
15. Tieu S, Charchoglyan A, Paulsen L, Wagter-Lesperance LC, Shandilya UK, Bridle BW, Mallard BA, Karrow NA (2023). N-Acetylcysteine and Its Immunomodulatory Properties in Humans and Domesticated Animals. Antioxidants (Basel). 12(10):1867. https://pubmed.ncbi.nlm.nih.gov/37891946/

Reviewed by Nancy Gao, M.Sc., Animal Biosciences, Dr. Niel Karrow, PhD, Chief Science Officer.