Do vitamin C and E supplements blunt your training gains?
In otherwise healthy lifters, high-dose vitamin C and E can blunt the cellular signals that drive training adaptation, even though getting the same vitamins from whole foods doesn't seem to cause the same problem.
For decades the logic seemed obvious: hard training generates free radicals, free radicals damage tissue, so mopping them up with antioxidant vitamins should help you recover and adapt faster. Several well-controlled trials have found the opposite is closer to the truth, at least at the doses people actually take.
The clearest demonstration came from a Norwegian trial that had healthy men run an 11-week interval program while taking 1000 mg vitamin C and 235 mg vitamin E a day. Both groups raised VO2max by about the same amount, but muscle biopsies told a different story: markers of mitochondrial biogenesis, including PGC-1α and cytochrome c oxidase, rose in the placebo group and flatlined or fell in the vitamin group. An earlier, widely cited trial pairing megadose vitamin C and E with exercise found it blocked the usual rise in insulin sensitivity and shut down that same PGC-1α pathway, along with the body’s own antioxidant enzymes. The mechanism makes sense once you know that the reactive oxygen species produced during exercise aren’t just damage — they’re part of the signal telling muscle to build more mitochondria and upgrade its own defenses. Neutralize the signal and you neutralize part of the adaptation.
Strength training tells a messier story. Individual trials have caught blunted anabolic signaling and smaller lean-mass gains in older lifters on high-dose vitamin C/E, but a 2020 meta-analysis pooling the strength-training data found no significant hit to final strength, and a broader 2024 meta-analysis across 13 trials found no effect on VO2max, strength, or overall performance in either direction.
Food doesn’t seem to cause the same problem
Get the same nutrients from oranges, berries, and leafy greens instead of a capsule, and the blunting effect doesn’t show up in the research. Dietary intake runs far below the gram-scale doses used in these trials, and it arrives bundled with hundreds of other plant compounds rather than isolated in a pill.
Who might reasonably still supplement
Someone sick, eating a genuinely restrictive diet, training at extreme volumes with real antioxidant depletion, or peaking for a single high-stakes event — where blunting months-away adaptation is irrelevant — has a defensible case for short-term use. A healthy lifter trying to build muscle or fitness over a training block does not; the upside is unproven and the mechanistic downside is real.