How to Take Vitamin C: Dosage, Timing, Duration

Vitamin C is an ordinary dietary supplement, so here, unlike with prescription drugs, we can talk about practical dosing. But "more" does not mean "better": absorption has a limit, and megadoses can interfere with training adaptation. Our editorial team explains how much vitamin C is needed, when to take it and for how long.

How Much Vitamin C Is Really Needed

Official norms differ depending on the country. The American recommended daily allowance (RDA) is 90 mg for men and 75 mg for women, and for smokers 35 mg more due to increased oxidative stress. The European agency EFSA in 2013 set a reference intake of 110 mg for men and 95 mg for women.

These figures are calculated for healthy people and provide almost complete tissue saturation. A pharmacokinetic study by Levine and colleagues (1996) showed that the plasma concentration of ascorbate reaches a plateau at an intake of approximately 200 mg per day, and leukocytes are saturated even earlier. Larger amounts are absorbed by the body increasingly poorly.

Athletes lose a certain amount of vitamin C through sweat and have a higher level of oxidative stress, but there is no convincing evidence that their requirement exceeds the usual one by several times. Systematic reviews conclude that a diet with enough vegetables and fruits usually covers the requirement even under heavy loads.

A supplement makes sense when the diet is poor in plant foods, during periods of extreme exertion (multi-day competitions, training camps in a cold climate) and also for smokers. For reference: one serving of bell pepper, kiwi or orange contains from 50 to over 100 mg of vitamin C.

Doses for Different Goals

Practical dosing depends on the goal. For "insuring" the diet, 100–250 mg per day is enough. This range guarantees plasma saturation, does not cause side effects and does not noticeably affect training adaptation.

For the prevention of colds during extreme exertion, the most cited basis is the Cochrane review by Hemilä and Chalker (2013). In studies involving marathon runners, skiers and military personnel during training, regular intake of at least 200 mg per day roughly halved the risk of a cold. In the general population no such effect was observed.

Doses of 500–1000 mg are widely available for sale, but for a healthy person they are mostly excessive: a significant part of the substance is excreted. Taking 1 g or more daily throughout a training block has been linked by studies to a blunting of markers of mitochondrial adaptation (Gomez-Cabrera et al., 2008; Paulsen et al., 2014).

The tolerable upper intake level of 2000 mg per day is not a recommendation. It is the limit above which the likelihood of digestive disorders and other undesirable effects increases. Our editorial team does not recommend constantly taking megadoses without medical indications.

Timing and Distribution of Doses

Since ascorbate transport in the intestine becomes saturated, the percentage absorbed decreases as the single dose grows. Therefore 2 doses of 250 mg provide better bioavailability than 500 mg at once. For doses over 500 mg, dividing into several intakes is especially appropriate.

Vitamin C can be taken regardless of meals, but together with food it irritates the stomach less often. In addition, taking it with plant food enhances the absorption of non-heme iron — a useful bonus for vegetarians and female athletes with low iron stores.

As for timing relative to training, there is one specific application: combination with gelatin or collagen. In the study by Shaw and colleagues (2017), 15 g of gelatin together with vitamin C an hour before a short jumping load increased markers of collagen synthesis. Here vitamin C acts as a cofactor of the enzymes that form collagen fibers.

If your goal is maximum adaptation to endurance training, it is logical not to take high doses of antioxidants immediately before and after a session. Moderate doses at other times of the day most likely do not significantly affect the training signal.

Duration and Periodization

Vitamin C does not accumulate in the body in large amounts, so to maintain saturation it must be obtained daily — from food or from a supplement. "Course" intake for 2–3 weeks with breaks has no physiological justification for moderate doses.

For high doses, on the other hand, reasonable periodization makes sense. Many sports nutritionists advise taking 500–1000 mg only in specific periods: during competition series, flights, training camps in the cold or when in contact with sick people. In the basic preparatory period the dietary norm is enough.

In the Cochrane studies the effect of cold prevention was observed with regular daily intake before and during the period of exertion. Starting to take vitamin C only after symptoms appear is less effective: the data on therapeutic intake are ambiguous.

If, after prolonged intake of megadoses, you decide to stop, our editorial team advises reducing the dose gradually over 1–2 weeks. The evidence for "rebound" deficiency is weak, but such an approach costs nothing.

Typical Mistakes

The most common mistake is to believe that 1000 mg daily is "definitely better" than 200 mg. A much smaller dose is enough to saturate tissues, and the excess is at best excreted and at worst causes digestive disorders and reduces the effect of training.

The second mistake is to ignore the vitamin C content in other products: sports drinks, "immune" complexes, effervescent tablets and gainers often already contain it. The total daily intake can imperceptibly exceed 2 g.

• do not exceed 2000 mg per day from all sources without medical indications;
• distribute doses over 500 mg across several intakes;
• do not take megadoses daily during blocks focused on adaptation;
• with kidney stones, hemochromatosis or G6PD deficiency — only after consulting a doctor.

The third mistake is to count on vitamin C as a means of treating a cold. It can slightly shorten the duration of symptoms with regular intake, but it does not replace rest, sleep and seeing a doctor in case of complications.

Finally, vitamin C should not be confused with an "energy drink." Taking ascorbic acid before training does not increase strength or endurance in people without a deficiency.

Editorial Conclusions

For most athletes, the optimal intake of vitamin C is 100–250 mg per day from food and, if needed, from a supplement. This is enough to saturate the plasma and tissues.

Higher doses — 200–1000 mg — make sense during periods of extreme exertion, when the risk of colds increases. Constant daily intake of gram-sized doses during training blocks can blunt adaptation.

Distribute doses, take them with food, account for vitamin C from other products, and do not exceed 2 g per day without medical indications.

Also read our materials "Vitamin C: Forms and Which to Choose," "What to Combine Vitamin C With" and "Side Effects of Vitamin C."

References

1. Levine M, Conry-Cantilena C, Wang Y, et al. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proc Natl Acad Sci U S A. 1996;93(8):3704–3709.
2. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;(1):CD000980.
3. Institute of Medicine. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: National Academies Press; 2000.
4. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for vitamin C. EFSA Journal. 2013;11(11):3418.
5. Shaw G, Lee-Barthel A, Ross ML, Wang B, Baar K. Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis. Am J Clin Nutr. 2017;105(1):136–143.
6. 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.
7. 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.