Vitamin C and Exercise: Immunity, Recovery and Antioxidant Function

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin involved in immune function, collagen formation, antioxidant protection and the absorption of non-haem iron.

The human body cannot produce vitamin C, so it must be obtained regularly from food or, when necessary, dietary supplements.

Vitamin C is of particular interest to athletes because of its relationship with immune function during periods of intensive exercise. However, high-dose supplementation has not been shown to directly increase strength, endurance or muscle growth.

What does vitamin C do?

Vitamin C contributes to:

• normal immune-system function,
• the protection of cells from oxidative stress,
• normal energy-yielding metabolism,
• the reduction of tiredness and fatigue,
• normal nervous-system function,
• normal psychological function,
• increased iron absorption,
• regeneration of the reduced form of vitamin E,
• normal collagen formation.

Through its role in collagen formation, vitamin C supports the normal function of bones, cartilage, blood vessels, skin, teeth and gums.

Vitamin C and intensive physical exercise

The European Union has authorised the claim that vitamin C contributes to maintaining the normal function of the immune system during and after intensive physical exercise.

For this claim to be used on a food or supplement, the product must provide a daily intake of 200 mg of vitamin C in addition to the normal diet.

This does not mean that vitamin C prevents all infections or eliminates the physiological effects of demanding training. It means that adequate intake supports normal immune function during periods of increased physical stress.

Exercise, oxidative stress and free radicals

Exercise temporarily increases the production of reactive oxygen species. These compounds are often described as free radicals and may contribute to oxidative stress when produced in excessive quantities.

However, reactive oxygen species are not exclusively harmful. They also act as signalling molecules involved in normal adaptations to exercise.

Vitamin C acts as an antioxidant and contributes to cellular protection. This does not mean that every increase in exercise-induced oxidative stress should be completely suppressed, because part of this response is involved in training adaptation.

Does vitamin C improve athletic performance?

Vitamin C is not considered a direct ergogenic supplement. It does not act like creatine, caffeine or carbohydrates and should not be expected to cause an immediate increase in strength, speed or endurance.

A 2023 review of randomised trials reported mixed findings. Most studies did not identify a clear performance benefit from high-dose vitamin C, and many administered it together with other antioxidants, making its individual effects difficult to determine.

Correcting a genuine deficiency may support normal physiological function and training capacity. Additional supplementation in an athlete who already meets their requirements has not been shown to provide a further ergogenic benefit.

Vitamin C and exercise recovery

Vitamin C supplements are frequently used to reduce muscle soreness, inflammation and markers of muscle damage following exercise. The scientific evidence is inconsistent.

Some studies have reported small reductions in selected markers of muscle damage or soreness, while others have found no meaningful differences in muscle function, inflammation or recovery.

A 2026 systematic review and meta-analysis concluded that vitamin C supplementation does not consistently modify inflammatory or oxidative-stress markers after exercise. It cannot therefore be regarded as an established recovery supplement.

Recovery depends more strongly on:

• sufficient protein and energy intake,
• carbohydrate replacement,
• hydration,
• adequate sleep,
• appropriate management of training load.

Vitamin C can form part of a balanced recovery diet, but it does not replace these fundamental factors.

Can high doses interfere with training adaptations?

There is concern regarding the long-term use of high-dose antioxidant vitamins close to training sessions.

In one randomised trial, a daily combination of 1,000 mg vitamin C and 235 mg vitamin E attenuated some cellular markers of mitochondrial adaptation following endurance training. However, improvements in maximal oxygen uptake and running performance were not significantly different from the placebo group.

A subsequent systematic review and meta-analysis found no significant reduction in improvements in maximal oxygen uptake, endurance performance, strength or lean mass following vitamin C and E supplementation. The researchers noted that larger and better-powered trials are still required.

There is no evidence that obtaining normal quantities of vitamin C from food impairs training adaptations. The concern primarily relates to chronic, unnecessary use of high-dose antioxidant supplements.

Vitamin C and immune function

Vitamin C supports several components of innate and adaptive immunity. It participates in white blood cell function, epithelial barrier maintenance and the protection of immune cells from oxidative stress.

In the general population, regular supplementation does not appear to substantially reduce the likelihood of developing a common cold. It may, however, produce a modest reduction in cold duration.

In studies involving marathon runners, skiers and soldiers exposed to extreme exercise or cold conditions, regular vitamin C supplementation was associated with a lower incidence of common colds. These findings relate to extreme physical stress and should not be generalised to all active individuals.

Starting vitamin C only after cold symptoms appear has not been shown to consistently reduce their duration or severity.

Vitamin C, collagen and connective tissue

Vitamin C is required for normal collagen formation. Collagen is a major structural component of tendons, ligaments, cartilage, bone and skin.

Severe vitamin C deficiency can impair collagen synthesis, wound healing and connective-tissue integrity. This does not mean that very high doses automatically accelerate healing or prevent sports injuries when vitamin C intake is already sufficient.

Vitamin C is often included in collagen products, but the effectiveness of such combinations depends on the complete formulation, dosage, diet and exercise programme.

Vitamin C and iron absorption

Vitamin C can increase the absorption of non-haem iron, the form mainly found in plant foods.

A meal containing lentils, beans or leafy vegetables can be combined with peppers, tomatoes, kiwifruit or citrus fruit. This may be particularly useful for vegetarian and vegan athletes.

This property does not justify uncontrolled high-dose supplementation, especially in people with iron-overload disorders.

Dietary sources of vitamin C

Good sources include:

• red and green peppers,
• oranges and other citrus fruits,
• kiwifruit,
• strawberries,
• broccoli,
• Brussels sprouts,
• tomatoes and tomato juice,
• potatoes,
• cantaloupe.

Fruit and vegetables are the principal natural sources. Vitamin C is sensitive to heat and dissolves in water, so prolonged cooking or boiling may reduce the vitamin C content of food.

Eating a variety of fresh or lightly cooked fruit and vegetables can help meet daily requirements.

How much vitamin C is required?

The European Food Safety Authority has established population reference intakes of:

• 110 mg per day for adult men,
• 95 mg per day for adult women.

These values refer to total daily intake from all dietary sources and are not recommended supplement doses.

Most people can meet these requirements through a diet containing adequate fruit and vegetables.

Do athletes require more vitamin C?

There is no separate daily vitamin C requirement that applies to every athlete.

Requirements and deficiency risk may be influenced by:

• overall dietary quality,
• energy intake,
• fruit and vegetable consumption,
• training load,
• exposure to very cold conditions,
• smoking,
• malabsorption or chronic disease.

Athletes following restrictive diets, consuming very little fruit and vegetables or experiencing prolonged periods of intensive physical stress may have a greater risk of inadequate intake.

This does not mean that every athlete requires a daily high-dose supplement.

When may a supplement be useful?

Supplementation may be considered when:

• fruit and vegetable intake is insufficient,
• a restrictive diet is being followed,
• there is an increased risk of deficiency,
• nutritional requirements cannot be met through food,
• a health professional has recommended supplementation.

Vitamin C is available alone or as part of vitamin and mineral products and multivitamin formulas.

Total intake should be checked before combining products because multivitamins, electrolyte supplements and immune-support formulas may already contain vitamin C.

Are special forms of vitamin C better?

The most common supplemental form is ascorbic acid. Other forms include sodium ascorbate, calcium ascorbate, mineral ascorbates and combinations with bioflavonoids.

Available evidence does not show a consistent and clinically meaningful advantage of one particular form in terms of total bioavailability or effectiveness. Supplemental ascorbic acid has bioavailability comparable to naturally occurring vitamin C in foods.

Buffered forms and mineral ascorbates may be better tolerated by some individuals, but this primarily relates to individual gastrointestinal tolerance.

When should vitamin C be taken?

There is no mandatory time for taking vitamin C.

It may be taken:

• with a meal,
• in smaller divided doses,
• according to the product instructions.

Taking it with food may reduce digestive discomfort in sensitive individuals.

There is insufficient evidence that taking vitamin C immediately before or after exercise provides a greater benefit. Consistently meeting daily requirements is more important than precise timing.

Are very high doses necessary?

Vitamin C absorption is tightly regulated. At daily intakes of approximately 100 mg, cells approach saturation, while plasma concentrations increase only marginally beyond approximately 200 mg. Larger quantities are increasingly excreted in urine.

Doses of several grams therefore do not provide proportionally greater benefits than an adequate intake.

Adverse effects and precautions

Vitamin C has generally low toxicity. High doses may cause:

• diarrhoea,
• nausea,
• abdominal cramps,
• digestive discomfort.

The United States tolerable upper intake level for adults is 2,000 mg per day from food and supplements combined. This is a safety limit, not a recommended daily dose.

Additional caution is required for people with:

• kidney disease,
• hyperoxaluria or certain types of kidney stones,
• hereditary haemochromatosis,
• cancer treatment,
• regular medication use.

High doses may increase iron absorption and could worsen iron overload in people with haemochromatosis. Antioxidant supplementation during chemotherapy or radiotherapy should be discussed with the treating physician.

Conclusion

Vitamin C is required for normal immune function, antioxidant protection, collagen formation and non-haem iron absorption.

Adequate intake is important for athletes, particularly during intensive training, restrictive dieting or periods in which dietary intake is inadequate.

Vitamin C is not a direct performance-enhancing supplement. Available evidence does not support the routine use of very high doses to increase strength, endurance or muscle recovery.

Priority should be given to a balanced diet containing a variety of fruit and vegetables. Supplements should be used to address a genuine nutritional need rather than replace the fundamental components of diet and recovery.

Frequently asked questions

Does vitamin C support athletes’ immune systems?

Yes. Vitamin C contributes to normal immune-system function. The European Union also recognises its contribution to maintaining normal immune function during and after intensive physical exercise under specific intake conditions.

Does vitamin C reduce muscle soreness?

Research findings are mixed. Some studies have identified small improvements in selected markers, but there is no consistent evidence of a substantial effect on muscle soreness or recovery.

Does vitamin C improve endurance?

It has not been shown to directly increase endurance in athletes with adequate vitamin C intake. Correcting a deficiency can support normal function but does not make vitamin C an ergogenic supplement.

Should it be taken after exercise?

There is no mandatory timing protocol. Meeting daily requirements consistently is more important than taking vitamin C immediately before or after exercise.

Is 1,000 mg per day necessary?

Not for most people. European population reference intakes are 110 mg for men and 95 mg for women. A 1,000 mg dose is substantially higher than normal nutritional requirements and has not been shown to provide proportionally greater benefits.

Can vitamin C be taken with iron?

Yes. Vitamin C can increase non-haem iron absorption. People with haemochromatosis or other iron-overload disorders should avoid high doses unless medically advised.

Is liposomal vitamin C better?

There is insufficient evidence to show that liposomal vitamin C is necessary or clinically superior for a healthy person who can absorb conventional vitamin C normally.

References

1. National Institutes of Health, Office of Dietary Supplements. “Vitamin C – Health Professional Fact Sheet.” Updated July 31, 2025.
2. EFSA Panel on Dietetic Products, Nutrition and Allergies. “Scientific Opinion on Dietary Reference Values for Vitamin C.” EFSA Journal, 2013.
3. European Commission. “Commission Regulation (EU) No 432/2012: Permitted Health Claims Made on Foods.” Consolidated version, August 20, 2025.
4. EFSA Panel on Dietetic Products, Nutrition and Allergies. “Scientific Opinion on the Substantiation of Health Claims Related to Vitamin C.” EFSA Journal, 2009.
5. Carr A.C. and Maggini S. “Vitamin C and Immune Function.” Nutrients, 2017.
6. Hemilä H. and Chalker E. “Vitamin C for Preventing and Treating the Common Cold.” Cochrane Database of Systematic Reviews, 2013.
7. Paulsen 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.
8. Clifford T. et al. “The Effects of Vitamin C and E on Exercise-Induced Physiological Adaptations: A Systematic Review and Meta-analysis of Randomized Controlled Trials.” Critical Reviews in Food Science and Nutrition, 2020.
9. Rogers D.R., Lawlor D.J. and Moeller J.L. “Vitamin C Supplementation and Athletic Performance: A Review.” Current Sports Medicine Reports, 2023.
10. Candeloro B.M. et al. “Effect of Vitamin C Supplementation on Post-Exercise Recovery: A Systematic Review and Meta-Analysis of Randomized Double-Blind Placebo Trials.” Clinical Nutrition ESPEN, 2026.