Written by the Nuvirox Research Team
Key points
- Oxidative stress is a real, measurable imbalance — but it is not a diagnosis, and no clinic test tells you whether it explains your tiredness.
- Randomized trials found that high-dose vitamin C and E supplementation blunted the mitochondrial adaptations to endurance training rather than improving them.
- Reactive oxygen species are signals as well as damage. Suppressing them indiscriminately suppresses the repair response too.
Short answer: oxidative stress is real, but it is a mechanism, not an explanation for your fatigue — and the trials on antioxidant supplements went the wrong way. Reactive oxygen species genuinely accumulate with age, illness, and hard training. What does not follow is that mopping them up with supplements restores energy. In several well-conducted randomized controlled trials, high-dose vitamin C and E did not improve outcomes; they blunted the very mitochondrial adaptations that make people feel more capable. The fair reading is that oxidative stress is a useful concept for understanding cellular aging and a poor one for guiding a supplement purchase.
What is oxidative stress, precisely?
Every cell that makes ATP produces reactive oxygen species as a by-product. Electrons leaking from the mitochondrial transport chain react with oxygen to form superoxide and its downstream relatives. This is not a malfunction; it is a normal feature of aerobic metabolism.
Cells maintain an extensive defensive apparatus in response: superoxide dismutase, catalase, glutathione peroxidase, and the glutathione pool itself. "Oxidative stress" is the specific situation where production outpaces that defence, allowing ROS to damage lipids, proteins, and DNA. It is a ratio, not a substance, which is precisely why you cannot buy a test for it at a pharmacy.
Does oxidative stress cause fatigue?
The connection is plausible and indirect. Oxidative damage to mitochondrial components could reduce ATP output, and reduced ATP output could plausibly feel like tiredness. Markers of oxidative stress are elevated in a long list of conditions where fatigue is prominent — chronic kidney disease, heart failure, inflammatory conditions, iron overload, and ME/CFS among them.
But elevated markers in fatiguing conditions do not establish direction. Oxidative stress rises in almost every state of illness, inactivity, and poor sleep, which makes it a very weak discriminator. If a marker is elevated in nearly everyone who feels unwell, it does not explain why any particular person feels unwell.
What human studies actually show
Paulsen and colleagues, 2014: high-dose vitamin C and E blunted training adaptation. Fifty-four young men and women were randomized to 1,000 mg vitamin C plus 235 mg vitamin E daily, or placebo, for eleven weeks of supervised endurance training. The supplemented group showed blunted increases in mitochondrial proteins including COX4 — markers directly tied to muscular endurance. Running performance and VO2 changes were not detectably different, but the cellular machinery that underlies long-term improvement responded less.
The same group found a comparable pattern with strength training. In a parallel ten-week strength-training study, vitamin C and E supplementation altered protein signalling after a session in ways consistent with reduced hypertrophic response. The authors concluded the supplements interfered with the acute cellular response to heavy-load resistance exercise.
Independent replication reached similar conclusions. A 2015 double-blinded trial in eleven healthy young males using vitamin C and E found the supplements prevented some of the cellular adaptations to endurance training. Small, but pointing the same direction.
The honest counterweight in the other direction: not every trial found harm. A 2022 randomized trial of vitamin C and E during resistance training in trained men found blunting of upper-body strength and hypertrophy adaptations, but also reduced gains in visceral adipose tissue during an energy surplus. And several trials found negligible effects overall. The literature is not unanimous that antioxidants are harmful — it is fairly consistent that they are not helpful for the thing people buy them for.
Why would blocking damage make things worse?
Because the ROS produced during exercise are not only damage — they are the signal. Contracting muscle generates ROS, and those ROS activate redox-sensitive transcription factors that drive mitochondrial biogenesis and upregulate the body's own antioxidant enzymes. Flood the system with exogenous antioxidants and the signal is muffled before it can be read.
This is hormesis: a stressor large enough to trigger adaptation, small enough not to cause lasting harm. It applies to exercise, to heat, to cold, and to fasting. It is also why the intuition that "less damage must be better" fails here.
What the oxidative stress framing won't do
It will not give you a number to act on. There is no validated clinical test of whole-body oxidative stress. Research uses markers like F2-isoprostanes and malondialdehyde; direct-to-consumer panels offering an "oxidative stress score" are not measuring anything with an established treatment pathway.
It will not identify why you are tired. If tiredness is new, persistent for more than a few weeks, or accompanied by breathlessness, weight change, fever, or unusual bleeding or bruising, that is a conversation with a doctor rather than a reason to add an antioxidant. The glutathione question runs into exactly the same wall: strong mechanism, weak oral bioavailability, thin human outcome data.
And it will not be fixed by megadosing. The dose-response in these trials is not a straight line. More is a different intervention, not a stronger one.
Frequently asked questions
Should I stop taking vitamin C entirely?
No. Vitamin C is an essential nutrient, and dietary intake is not what these trials tested. The trials used roughly ten to twenty times the recommended intake, taken daily around training. Meeting your requirement through food or a modest multivitamin is a different situation from gram-dosing.
What about antioxidants from food?
No trial has shown that fruit and vegetable intake blunts training adaptation, and the observational evidence for a diet rich in them is broadly favourable. The blunting signal comes specifically from isolated, high-dose supplements.
Does oxidative stress cause aging?
The pure free radical theory of aging has not held up well. It has been substantially revised into a more nuanced picture where ROS act as signals and where damage is only one of several interacting hallmarks, alongside cellular senescence, inflammation, and metabolic changes.
If I am not training, do the blunting findings apply to me?
Less directly. The blunting studies specifically measured adaptation to exercise. What they do establish more generally is that suppressing ROS is not automatically beneficial, which should temper expectations about antioxidants improving baseline energy in sedentary people too.
Is there any group where antioxidant supplementation clearly helps fatigue?
Correcting a genuine deficiency helps. Beyond deficiency correction, high-quality trials showing that antioxidant supplements reduce fatigue in otherwise healthy people are scarce.
From Nuvirox
Why we formulated NAD+ Restore
NAD+ Restore contains polyphenols — trans-resveratrol and quercetin — but we position them honestly. They are studied alongside NAD+ pathways for cellular health support, not sold as antioxidants that will make you feel more energetic.
- 500 mg Nicotinamide Riboside Chloride (NR) — one of the two most-researched NAD+ precursors, within the dose range used in published human trials.
- 150 mg trans-resveratrol (Japanese Knotweed) and 50 mg quercetin (Sophora japonica) — polyphenols studied alongside NAD+ pathways for cellular health support.
- 10 mg galactomannans from fenugreek, to support absorption.
- 60-day money-back guarantee — long enough to actually evaluate it the way the research says you should.
The bottom line
Oxidative stress is a legitimate piece of cell biology and a poor consumer health concept. The randomized trials that tested the obvious implication — take antioxidants, feel better, adapt faster — found blunted adaptation instead. If you want to reduce the oxidative burden on your mitochondria, training, sleep, and not smoking have far better evidence behind them than any capsule, and none of them interfere with the signalling that makes adaptation possible.
References
- Paulsen G, Cumming KT, Holden G, et al. Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomised, controlled trial. The Journal of Physiology. 2014;592(8):1887–1901. DOI: 10.1113/jphysiol.2013.267419
- Paulsen G, Hamarsland H, Cumming KT, et al. Vitamin C and E supplementation alters protein signalling after a strength training session, but not muscle growth during 10 weeks of training. The Journal of Physiology. 2014. PMCID: PMC4270502
- Morrison D, Hughes J, Della Gatta PA, et al. Vitamin C and E supplementation prevents some of the cellular adaptations to endurance-training in humans. Free Radical Biology and Medicine. 2015. PMID: 26482865
- Dutra MT, et al. Antioxidant vitamin supplementation on muscle adaptations to resistance training: a double-blind, randomized controlled trial. Nutrition. 2022. PMID: 36283241
- Custodero C, Mankowski RT, Lee SA, et al. Evidence-based nutritional and pharmacological interventions targeting chronic low-grade inflammation in middle-age and older adults: a systematic review and meta-analysis. Ageing Research Reviews. 2018;46:42–59. PMID: 29803716. DOI: 10.1016/j.arr.2018.05.004
- Camacho-Pereira J, Tarragó MG, Chini CCS, et al. CD38 dictates age-related NAD decline and mitochondrial dysfunction through an SIRT3-dependent mechanism. Cell Metabolism. 2016;23(6):1127–1139. PMID: 27304511. DOI: 10.1016/j.cmet.2016.05.006
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for professional medical advice.