In 30 seconds
- EFSA sets 110 mg a day for men and 95 mg for women; at around 100 mg a day, cells are already practically saturated.
- At 200 mg a day on top of the recommended intake, the EU authorises this claim: “Vitamin C contributes to maintain the normal function of the immune system during and after intense physical exercise.”
- In 18 trials, vitamin C reduced markers of oxidative stress and inflammation after exercise, but not muscle soreness or loss of strength.
- With 1,000 mg a day for 11 weeks, VO2max improved just as much as with placebo, but some muscle adaptations were blunted.
Vitamin C is one of the most studied vitamins in athletes. For people who undergo very heavy physical exertion, it has its own authorised claim; for recovery and performance, the data are more modest, and with megadoses an important nuance appears.
To understand the studies
What your body uses and the maximum
What it is and what it does
It is a water-soluble vitamin that acts as an antioxidant. Your body stores between about 300 mg and 2 g in total. It is concentrated in white blood cells, the eyes and the adrenal glands; its level in the blood is low 2.
European regulations authorise, among others, these two claims 9:
- Vitamin C contributes to the normal function of the immune system.
- Riboflavin (vitamin B2), vitamins B6, B12 and C, niacin, pantothenic acid and folate contribute to the reduction of tiredness and fatigue.
A varied and balanced diet and a healthy lifestyle are important.
Two facts help in understanding the studies. At around 100 mg a day, cells are already practically saturated. And above 1 g a day, less than half is absorbed 2.
Level of evidence by outcome
| Outcome | Evidence | What the data show |
|---|---|---|
| Immunity during intense exercise | High | Authorised claim in the EU at 200 mg a day on top of the recommended daily intake. |
| Oxidative stress and inflammation after exercise | Moderate | Fewer markers of oxidative stress and lower IL-6 in the following 2 hours, in 18 trials. |
| Muscle soreness, muscle damage and strength | No clear effect | No change in muscle soreness, creatine kinase or strength in the same 18 trials. |
| Lung function after exercise | Preliminary | 48% less decline in lung function after exercise, in 3 trials with 40 people. |
| Megadoses and training adaptations | Moderate | With 1,000 mg a day plus vitamin E, VO2max improved just as much, but muscle adaptation signals were blunted. |
The rating is our own, based on the type of studies, their number and the consistency of the results.
The key studies
| Study | Type | Sample | Outcome |
|---|---|---|---|
| Righi et al., 2020 | Meta-analysis | 18 trials, 313 people | With 400-3,000 mg: less lipid peroxidation up to 2 hours later and lower IL-6. No effect on muscle soreness, creatine kinase or strength. 4 |
| Paulsen et al., 2014 | Randomised trial | 54 men and women, 11 weeks of training | 1,000 mg of vitamin C and 235 mg of vitamin E a day: no change in VO2max or running compared with placebo; markers of new mitochondria rose only with placebo. 5 |
| Gomez-Cabrera et al., 2008 | Trial in humans and rats | 14 men (8 weeks) and 24 rats | 1 g a day. In the rats, lower endurance capacity. The authors conclude that it blunts some cellular adaptations to exercise. 6 |
| Hemilä, 2013 | Meta-analysis | 3 trials, 40 people | The fall in FEV1 after exercise was 48% smaller with vitamin C. 7 |
| EFSA, 2013 | Reference values | EFSA Nutrition Panel | Population reference intake of 110 mg a day for men and 95 mg for women, to maintain about 50 µmol/L in the blood. 1 |
Immunity and intense exertion
The Cochrane review by Hemilä and Chalker pooled the placebo-controlled trials that used at least 200 mg of vitamin C a day. It separated two types of people: the general population and those under very heavy physical exertion, such as marathon runners, skiers and soldiers on subarctic exercises 3.
For intense exercise, the EU authorises this claim, at 200 mg a day on top of the recommended daily intake 9:
- Vitamin C contributes to maintain the normal function of the immune system during and after intense physical exercise.
Muscle damage and recovery
Righi's meta-analysis pooled 18 trials with 313 healthy adults. They took between 400 and 3,000 mg of vitamin C, for 1 to 28 days, before an exercise session 4.
- What went down: lipid peroxidation, a marker of oxidative stress, immediately after exercise and up to 2 hours later. So did the rise in IL-6, a signal of inflammation 4.
- What did not change: muscle soreness, creatine kinase (a marker of muscle damage), C-reactive protein, cortisol and strength 4.
In practice: less oxidative stress measured in the blood, but no recovery you would notice.
11 weeks of training
Placebo versus megadoses of vitamins C and E
Do megadoses blunt adaptations?
This is the most interesting nuance for anyone who exercises. In Paulsen's trial, 54 men and women trained for 11 weeks, mostly running, 3-4 times a week. Half took 1,000 mg of vitamin C and 235 mg of vitamin E a day 5.
VO2max and running performance improved equally in both groups. But the markers of new mitochondria forming rose only in the placebo group 5.
The Gomez-Cabrera study, with 1 g of vitamin C a day, pointed in the same direction: in rats it worsened endurance capacity, and the authors conclude that vitamin C blunts some cellular adaptations to exercise 6.
The explanation given by the NIH: the free radicals produced by exercise are also a signal for the muscle to adapt. High doses of antioxidants can dampen that signal 8. These are doses of 1,000 mg, more than nine times a man's daily reference intake.
Vitamin C and breathing
A small meta-analysis pooled 3 trials with 40 people. Vitamin C reduced the fall in lung function (FEV1) after exercise by 48% 7. The author considers this enough to keep researching it in active people 7.
Where it is found
Vitamin C in common foods
How much you need
The European Food Safety Authority set its figures with one goal: to maintain adequate stores, with about 50 µmol/L of vitamin C in fasting blood 1:
| Average requirement | Population reference intake | |
|---|---|---|
| Men | 90 mg | 110 mg |
| Women | 80 mg | 95 mg |
| Pregnancy | — | 105 mg |
| Breastfeeding | — | 155 mg |
Source: EFSA, 2013. The population reference intake covers the needs of almost the whole population.
- If you smoke: the US reference adds 35 mg a day 2.
- Where it is found: a medium orange provides about 70 mg; a kiwi, 64 mg; and half a cup of raw red pepper, 95 mg 2.
- Maximum: the US reference sets it at 2,000 mg a day for adults; above that, diarrhoea, nausea and stomach discomfort may appear 2.
- Kidney stones: high doses could encourage them in people who are prone to them 2. If that applies to you, check with your doctor.
You have the practical version, with more foods, in vitamin C and sport: how much you need if you exercise.
What we do not know yet
- Dietary doses: the studies on this page use 200 mg or more a day; less is known about what happens with amounts like those in the diet.
- Who benefits: the trials with intense exertion were carried out in very specific groups, with extreme loads or a lot of cold 3.
- Adaptations: the most cited trial combined vitamins C and E for 11 weeks, so it does not separate the effect of each one 5.
The vitamin C in Nitrus
Nitrus Isotonic provides 80 mg of vitamin C per serving, 100% of the reference value, together with the other 12 vitamins. Vitamin C contributes to the normal function of the immune system.
It is completed by five electrolytes, BCAAs, glutamine and taurine. If you are interested in the other vitamins, you have them in B vitamins, energy and tiredness.
Frequently asked questions
Does vitamin C support the immune system if you exercise?
For intense exercise, the EU authorises this claim: “Vitamin C contributes to maintain the normal function of the immune system during and after intense physical exercise.” The effect is obtained with 200 mg a day, on top of the recommended daily intake.
Does vitamin C reduce muscle soreness?
Not according to the studies. In a meta-analysis of 18 trials it reduced markers of oxidative stress and inflammation after exercise, but it did not change muscle soreness, creatine kinase or loss of strength.
Does taking a lot of vitamin C affect training?
Megadoses may blunt some adaptations. In an 11-week trial, 1,000 mg of vitamin C with vitamin E did not change the improvement in VO2max, but it blunted the markers of new mitochondria forming in the muscle.
What is the maximum dose of vitamin C?
The US reference sets the maximum for adults at 2,000 mg a day; above that, digestive discomfort may appear. Above 1 g a day, less than half is absorbed.
Sources
- EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific opinion on dietary reference values for vitamin C. EFSA Journal. 2013;11(11):3418. View publication
- Office of Dietary Supplements, National Institutes of Health. Vitamin C: fact sheet for health professionals. Updated 31 July 2025. View publication
- Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;(1):CD000980. View publication
- Righi NC, Schuch FB, De Nardi AT, et al. Effects of vitamin C on oxidative stress, inflammation, muscle soreness, and strength following acute exercise: meta-analyses of randomized clinical trials. Eur J Nutr. 2020;59(7):2827-2839. View publication
- 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. J Physiol. 2014;592(8):1887-1901. View publication
- Gomez-Cabrera MC, Domenech E, Romagnoli M, et al. Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance. Am J Clin Nutr. 2008;87(1):142-149. View publication
- Hemilä H. Vitamin C may alleviate exercise-induced bronchoconstriction: a meta-analysis. BMJ Open. 2013;3(6):e002416. View publication
- Office of Dietary Supplements, National Institutes of Health. Dietary supplements for exercise and athletic performance: fact sheet for health professionals. View publication
- Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product.
