The Double-Edged Sword of Antioxidant Supplementation: How High-Dose Vitamins C/E Interfere with Training Adaptations

This article is based on peer-reviewed research from international sports science journals, providing an in-depth analysis of the effects of “antioxidants” on athletic performance, and combining Taiwan’s local cycling and race scenarios to offer actionable training nutrition recommendations.

Free radicals produced by exercise were once viewed as purely harmful, but recent research has found that moderate oxidative stress is a “signal” for training adaptation. High-dose antioxidants may instead interfere with adaptation.

In Taiwan’s endurance sports community—whether it’s climbing enthusiasts tackling the Wuling ascent from the west, long-distance riders heading east through the Huatung Valley, or participants in Sun Moon Lake circumnavigation, Taroko Marathon, or 226 km Ironman triathlons—the topic of “antioxidants” matters because it directly determines whether you can maintain your pace in the latter stages of a race, avoid cramping and hitting the wall, and recover effectively between consecutive training days. Many amateur athletes pour all their effort into power training and equipment upgrades while neglecting nutrition—this “free margin of improvement.” In fact, when training volume and equipment are comparable, the quality of nutritional strategy is often the key variable separating finishing from dropping out, and personal bests from collapse. This article will walk you through the complete context—from cellular molecular mechanisms, randomized controlled trial evidence, to dose-response curves and practical application—debunking long-standing myths so that your fueling strategy is truly built on science.

Academic Research Review

Regarding the scientific exploration of “antioxidants,” top international journals have accumulated rich and rigorous evidence. Below are several representative studies selected for their value in methodological design, sample populations, and strength of conclusions, collectively forming our current understanding of this topic:

1. Gomez-Cabrera MC et al. (2008, AJCN) found that vitamin C inhibits mitochondrial biogenesis adaptation.

2. Ristow M et al. (2009, PNAS) confirmed that antioxidants block exercise-induced insulin sensitivity benefits.

3. Paulsen G et al. (2014, Journal of Physiology) showed that vitamin C+E blunts endurance training adaptation.

4. Merry TL and Ristow M (2016, Journal of Physiology) reviewed the signaling role of oxidative stress.

Looking at these studies as a whole, the scientific picture of “antioxidants” is not a single fixed conclusion but rather one that is continually revised and deepened as research methods advance. Early studies mostly used laboratory-controlled time trials or exhaustion tests; subsequent research gradually incorporated stable isotope tracing, muscle biopsies, functional magnetic resonance imaging (fMRI), and molecular biomarkers, allowing us to move from “observing phenomena” to “explaining mechanisms.” Notably, most high-quality studies employed a randomized crossover design, where each subject serves as both the experimental and control group, greatly reducing noise from individual differences. However, extrapolating research conclusions requires caution: the responses of well-trained subjects in the laboratory may not fully apply to general amateur athletes; the effects of a single acute intervention may not equal long-term chronic adaptation. When reading the “effect sizes” and “statistical significance” of these studies, we must also distinguish between “statistically significant” and “practically meaningful”—a 1% improvement might determine medal placement in elite competition, but its significance is relatively limited for recreational riders.

Core Mechanisms

Reactive oxygen species (ROS) produced by exercise are important signals that upregulate PGC-1α, antioxidant enzymes, and mitochondrial biogenesis (i.e., the hormesis effect). High-dose exogenous antioxidants scavenge these signaling molecules, blocking downstream adaptation. Moderate amounts of antioxidants from dietary sources are harmless, but pharmacological-dose supplementation becomes an obstacle.

To truly understand how “antioxidants” affect athletic performance, we must return to physiology at the cellular and systemic levels. Athletic performance is the result of multi-system coordination: the cardiovascular system handles oxygen and fuel delivery, muscle cells handle energy conversion and mechanical contraction, the central nervous system regulates motor unit recruitment and fatigue perception, while the gut and liver form the hub of nutrient absorption and metabolism. The reason the aforementioned mechanisms translate into measurable performance differences is precisely because they act on one (or more) critical link in this chain. The table below summarizes the key points of action at different physiological levels for this topic, helping you build a complete mechanistic picture:

| Level of Action | Key Mechanisms | Significance for Athletic Performance |

|—|—|—|

| Cellular/Molecular | Affects mitochondrial efficiency, enzyme activity, and signal transduction | Determines the efficiency of energy conversion and the direction of adaptation |

| Muscle Tissue | Regulates substrate utilization, buffering capacity, and contractile function | Affects sustainable power output and fatigue onset |

| Systemic Integration | Alters blood flow distribution, thermoregulation, and hormonal environment | Determines stability and safety during prolonged exercise |

| Central Nervous System | Regulates fatigue perception, drive, and motor unit recruitment | Affects “how tired it feels” and the ability to persevere |

The two dimensions of “dose-response” and “temporal dynamics” deserve special emphasis. The same nutritional intervention, at different dosages and different timing of intake, can produce vastly different or even opposite effects—this is precisely why many common recommendations remain one-sided. Only by understanding the mechanisms can we judge “when to use it, how much to use, and when to take it,” rather than blindly following trends.

Furthermore, the limiting factors of athletic performance shift dynamically with exercise intensity and duration: in short, high-intensity bursts, limitations often come from the phosphagen system and the accumulation of glycolytic byproducts; in multi-hour endurance efforts, limitations shift toward the combined effects of glycogen depletion, rising core temperature, fluid-electrolyte imbalance, and central fatigue. The reason “antioxidants” deserve in-depth discussion is precisely because they can selectively influence some of these limiting factors. This also reminds us that no nutritional strategy can be evaluated in isolation from the “exercise context”—a fueling rhythm suitable for a 40-minute criterium may not apply to a 6-hour climbing epic, and vice versa. The more thoroughly you understand the mechanisms, the more flexibly you can adjust across different race formats, rather than rigidly adhering to a fixed formula. This ability to “adjust according to context” is precisely the dividing line between amateur athletes and those who truly understand sports science.

Dose and Effect Relationship

In sports nutrition, “the dose determines both toxicity and benefit.” Too low a dose fails to reach the physiological threshold and is futile; too high a dose may trigger side effects, gastrointestinal discomfort, or even interfere with training adaptation in reverse. The table below organizes the dose-effect correspondence for “antioxidants” and serves as the most important quantitative reference when developing a personal fueling plan:

| Dose / Condition | Effect Description |

|—|—|

| Dietary sources | Harmless and beneficial |

| Vitamin C 1000 mg | May interfere with adaptation |

| Vitamin E 400 IU | Blunts training effects |

| Off-season/injury period | May be used short-term |

As can be seen from the table above, benefits often follow an “inverted U” or “threshold-plateau” curve: effects increase with dose until the effective threshold is reached, but beyond a certain plateau point, there are not only no additional benefits but also sharply rising marginal costs (side effects, gastrointestinal burden, financial expense). This means that “finding your own optimal dose” matters far more than “taking as much as possible.” It is recommended to progressively test different doses during training (not on race day), recording subjective feelings, gastrointestinal responses, and power data to build your own dose profile. Remember: the laboratory average is a starting point, not the endpoint; each individual’s body weight, metabolic rate, gut tolerance, and genetic background will cause the optimal dose to shift on an individual basis.

Differences Across Population Groups

The benefits of “antioxidants” are not equal for everyone. Age, sex, training status, body size, and genetic background all significantly modulate the magnitude of an individual’s response. Applying a one-size-fits-all recommendation while ignoring these differences is one of the most common mistakes in sports nutrition.

| Population Aspect | Response Characteristics | Practical Recommendations |

|—|—|—|

| Beginners vs. Advanced Athletes | Advanced athletes have more mature physiological adaptations; responses tend to be more stable but with smaller marginal benefits | Beginners should start conservatively with low doses to build tolerance first |

| Men vs. Women | Differences in body weight, hormonal cycles, and sweat composition affect dosage and requirements | Women should individualize based on body weight and pay attention to iron and energy availability |

| Young vs. Older Athletes | Older individuals often experience reduced absorption efficiency and anabolic resistance | Older individuals may require higher doses or better timing |

| Body Size Differences | Body weight directly affects the absolute amount calculated per mg/kg or g/kg | Always convert to a dose corresponding to individual body weight; avoid copying general rules |

When interpreting “individual differences,” one must also be wary of a common statistical pitfall: studies mostly report “group average responses,” but beneath the average often lies enormous individual variability. In the same intervention, some may be strong responders, some non-responders, and some even negative responders. This is why even when a study shows “average effectiveness,” you still need to confirm which category you fall into through your own experimentation. The recommended approach is to conduct personalized A/B testing: across two training sessions with conditions kept as similar as possible, apply and withhold the strategy respectively, compare power, heart rate, and subjective feelings, and repeat several times before drawing conclusions. This empirical spirit of “using yourself as the sample” is the essential path from group science to individual prescription.

Taking the common amateur endurance population in Taiwan as an example, many are middle-aged cyclists over 35 who train around their work schedules. This group simultaneously faces declining recovery rates, insufficient sleep, and time pressure, so the “return on investment” of nutritional strategies is often higher than for younger elites—that is, correct nutritional intervention can yield relatively greater room for improvement. Female athletes, meanwhile, need to pay special attention to the effects of the menstrual cycle on metabolism and requirements, as well as whether energy availability is sufficient, avoiding the trap of low energy availability (LEA) in the pursuit of becoming lighter. After understanding population differences, you will realize: truly professional nutritional advice is always an individualized prescription that “varies from person to person,” not a one-size-fits-all slogan.

Practical Training Application

Theory must ultimately be put into practice on the training plan and the race course. Below is a practical framework for translating “antioxidants” into concrete training and race-day operations:

• Pre-Race Testing Principle: All nutritional strategies must first be rehearsed in training; “never try anything new on race day” is an iron rule. Gastrointestinal tolerance to new products takes time to build.

• Periodization Mindset: Align nutritional strategies with training phases—the base phase can focus on adaptation-oriented strategies, while the pre-season shifts to performance-oriented fueling optimization.

• Progressive Introduction: Start with low doses and low frequency, adjust gradually based on bodily responses, and build a personalized dosage and timing profile.

• Data Tracking: Combine power meter data, heart rate, subjective fatigue (RPE), and gastrointestinal comfort records to objectively evaluate whether an intervention is truly effective.

• Overall Context: Nutrition is one part of training, sleep, recovery, and psychology; a single supplement cannot compensate for sleep deprivation or flawed training design.

Using a one-week training schedule as an example, it is recommended to rehearse different fueling scenarios during key midweek high-intensity sessions (such as threshold intervals and repeated climbs) and the weekend long ride: high-intensity days emphasize rapid energy supply and central nervous system activation, while long-distance days emphasize sustained energy supply, gastrointestinal tolerance, and recovery. Through repeated rehearsal, your body can execute the optimal fueling rhythm “automatically” on race day, leaving mental resources for pacing and tactical decisions. Remember, the goal of a nutritional strategy is not to pursue theoretical perfection, but to remain stable and reliable under the fatigue, heat, and pressure of a real race course.

When executing a nutrition plan, the most common mistake many people make is “being serious only on race day while eating casually during regular training.” This is precisely putting the cart before the horse: regular training is the best laboratory for building gut tolerance, testing dosages, and cultivating fueling rhythm. If you hope to execute a fueling plan of 80 grams of carbohydrates per hour on race day, you must rehearse it repeatedly in training until your body becomes accustomed to it; if you intend to rely on a certain supplement, you must confirm in training that it is truly effective for you and has no side effects. It is recommended to integrate a nutrition log with your training log, recording the fueling content, intake timing, gastrointestinal responses, and performance data for each key session. After weeks to months of accumulation, the value of this personalized database will far exceed any general nutrition guide. Additionally, do not overlook the often-underestimated “post-training recovery fueling” component—the quality of recovery between consecutive training days often determines whether you can steadily accumulate training volume without injury, and training volume is the most fundamental engine of long-term progress. Treat nutrition as a part of training and take it seriously, rather than as an afterthought you scramble for before races—your progress curve will be noticeably different.

Local Application in Taiwan

Taiwan’s unique climate, terrain, and race culture add localized considerations to the application of “antioxidants.” Taiwan’s summer is hot and humid, with perceived temperatures often exceeding 35°C, and sweat rates and fluid/electrolyte losses far exceed those in research contexts from temperate countries. This means hydration and fueling recommendations from foreign literature often need to be “adjusted upward.” In events like the Westbound Wuling climb, which ascends from sea level to 3,275 meters, the appetite suppression of high altitude, low temperatures, and prolonged exercise pose a severe test for energy planning.

Regarding local fueling options, Taiwan’s abundant bananas, sweet potatoes, pineapples, sports drinks, and convenience store ready-to-eat foods can all be incorporated into fueling strategies; the extremely high density of convenience stores also makes mid-ride refueling on long rides relatively easy. It is recommended that Taiwanese cyclists planning classic routes such as Sun Moon Lake, Wuling, Beiyi, Buyan Pavilion, and Eastbound routes survey fueling points along the way in advance, and strengthen sodium and fluid supplementation in response to Taiwan’s humid and hot environment. Athletes in the Taroko Marathon, Taipei Marathon, and triathlon events across the island should likewise incorporate the above local climatic factors into their individualized nutrition plans to perform at their best under subtropical conditions.

Debunking Common Myths

Myth: The myth is that “the more antioxidants you take, the faster you recover.” In fact, high-dose supplementation suppresses the positive adaptations of exercise training, and dietary intake is sufficient.

These myths spread widely often because they “sound reasonable,” are easy to pass by word of mouth, or are amplified by marketing rhetoric. Yet the value of science lies in testing intuition with rigorous evidence: many seemingly obvious ideas fail to hold up under the scrutiny of randomized controlled trials. Sports nutrition is especially rife with oversimplified “panacea” style promotion that compresses complex dosage, timing, and individual differences into a single slogan. The next time you hear a categorical nutritional claim, it is worth asking: “What is the level of evidence for this claim? Who is the target population? Are the dosage and timing clearly specified?” Cultivating this evidence-based critical thinking is more valuable than memorizing any single conclusion, and it is a key step for amateur athletes moving toward scientific training.

Conclusion

“Antioxidants” is a topic in sports nutrition with both theoretical depth and practical value. From the academic evidence reviewed in this article, it is clear that their benefits are real, but they are by no means an unconditional panacea—the key lies in correct dosage, appropriate timing, individualized adjustment, and synergy with overall training, recovery, and sleep. For endurance sports enthusiasts in Taiwan, while mastering the scientific principles, it is equally important to combine local climate, terrain, and race characteristics to translate general rules into a personalized prescription suited to yourself. May every cyclist sweating on Wuling, in the rift valleys, and on round-island routes break through their limits through science-based nutritional strategies and enjoy the pure joy that sport brings. Before you next step onto the race course, do not forget—your bottle holds not just water and sugar, but an entire validated body of sports science.

Related Reading

• Antioxidant Supplementation and Training Adaptations: Interference of High-Dose Vitamins C and E with Adaptive Signaling
• The Controversy of Post-Exercise Antioxidant Supplementation: Research Evidence of Hindered Adaptive Signaling
• Vitamins C and E: The Antioxidant Dilemma—When the Antioxidants You Take Actually Block You from Getting Stronger
• Do Antioxidant Supplements Hold Back Your Training? A Sports Science Consultant Breaks Down the “Vitamin C/E vs. Diet” Debate