Vitamin C is needed for proper immune function. Strong stress on the body can increase the need for vitamin C. Therefore, high intakes of vitamin C might reduce the incidence of colds that occur when people exercise to the extreme. Well, does it?
Here’s what we know. Some statistic whizzes looked at studies on vitamin C supplements and the common cold including studies that looked at extreme exercisers (1). For the latter group, the stats people pooled data from studies that totaled 598 subjects who either ran a marathon, ran an ultramarathon, did a long ski camp, or were soldiers working in very demanding conditions. The stats people found a statistically significant effect of vitamin C supplementation on cold incidence for these 598 people. That number of people may sound impressive, but actually, it’s not. For one thing, the number of people getting the vitamin C falls well below the total number (since a lot of the people got placebo). Moreover, the individual study subjects varied a lot for factors that can affect vulnerability to colds. Also, no consistency existed among the studies for the vitamin C doses or the background dietary vitamin C intake. So, the combined results of these studies, though having merit, don’t give a final verdict.
Even if the studies are painting a true picture, the vitamin C isn’t providing a clear advantage for everyone. For instance, in one study (2), after a ultramarathon run, about 2/3 of the placebo group self reported having an upper respiratory tract infection. Only about a third of the group getting 600 mg of vitamin C per day reported infections. These infection rates may be artificially high since the subjects made their own analysis of infection. Still, the striking difference between groups is impressive. Even so, some of the placebo group got no infection and some of the vitamin C group did. To further complicate the situation, some studies report no effect for vitamin C. For example, in study of marathon runners (3), no difference was seen for colds between placebo and a group getting 1000 mg of vitamin C per day. One knock on the study is that the placebo group had only 14 people, a low number for this type study.
So, what can be concluded from all this? Well, we don’t have a wealth of ideal data. Even so, I think I can propose that vitamin C supplementation may help some people avoid a cold after a marathon, ultramarathon, or some other extreme exertions. However, a big question is: if the supplements do help some people, will they do anything for people who already have a good intake of vitamin C in their diet? In the negative results study cited in the last paragraph (3), the subjects were already consuming an average of over 400 mg/day of vitamin C. In addition, their plasma vitamin C readings were fairly high. In fact, based on another group’s work (4), the plasma values would be classified as near maximal. Thus, based on this one small study in marathoners, vitamin C supplementation may only help when dietary intake falls below optimal.
So, what constitutes optimal intake? It has been contended that for most people, the optimal intake can be set at 200 mg per day (4). With this intake, vitamin C contents of plasma, and certain white blood cells, reach near maximal values (4). Higher intakes, especially if spread out during the day, can raise plasma readings above this, but not by much. On the other hand, it can be speculated that not all vitamin C functions necessarily hit near peak capacities at 200 mg. Also, heavy exertion might temporarily raise needs.
So, here is my recommendation. For usual daily intake, shoot for 200 mg + an extra 100 mg in case some vitamin C functions need more than a 200 mg intake to max out. I recommend getting this from foods, not supplements. With foods, one not only gets the vitamin C, but also phytochemicals that can compliment vitamin C actions. Phytochemicals are compounds that are not strictly required like vitamins, but which can contribute to health. If you want to add extra vitamin C as supplements for a week before and after an event like a marathon, maybe that will help you prevent a cold. If you do that, you might want to take the supplements at meals that don’t have your highest dietary vitamin C levels. In the studies used by the statisticians, supplement doses ranged from 200 to 1000 mg. I am not a big fan of taking 1000 mg long term. That may not pose a huge health risk for everyone, but it could cause problems in some people.
You may be wondering about exercise training that is fairly heavy, but which doesn’t involve the extremes of something like a marathon run. We don’t have much data. One study did look at vitamin C supplements (1000 mg/day) in Israeli adolescent swimmers (5). No effect was seen for cold incidence, but length and severity were diminished in the males. The gender difference may indicate that the males consumed less vitamin C prior to the study. Possibly, if they had just upped their dietary vitamin C, it would have done as much as the high dose supplements. Therefore, in the absence of much data here, my recommendation matches what I said earlier for the extreme exercisers (except without the short term supplementation around an event).
I want to make one last comment here. Studies on nutrient supplement interventions often just look at one nutrient versus a placebo. That fits the drug model for research. However, for nutritional interventions, the best chance of seeing an effect on immune function probably involves multiple nutrients added to various lifestyle actions (ie enough sleep, exercise, hand washing, etc). However, studying all those factors at once becomes very problematic in terms of grant funding, getting the results published, and designing a study that can be interpreted clearly. Also, genetics likely plays a role in how any individual responds. So, recognize that everything I have written here about vitamin C and colds only hits one piece of a big puzzle.
- Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. The Cochrane Database of Systematic Reviews. 2013;CD000980.
- Peters EM, Goetzsche JM, Grobbelaar B, Noakes TD. Vitamin C supplementation reduces the incidence of postrace symptoms of upper-respiratory-tract infection in ultramarathon runners. American Journal of Clinical Nutrition 1993;57:170-174.
- Himmelstein SA, Robergs RA, Koehler KM, Lewis SL, Qualls CR. Vitamin C supplementation and upper respiratory tract infections in marathon runners. Journal of Exercise Physiology Online 1998;1:1-21.
- Frei B, Birlouez-Aragon I, Lykkesfeldt J. Authors’ perspective: What is the optimum intake of vitamin C in humans? Critical Reviews in Food Science and Nutrition. 2012;52:815-829.
- Constantini NW, Dubnov-Raz G, Eyal B-B, Berry EM, Cohen AH, Hemilä H. The effect of vitamin C on upper respiratory infections in adolescent swimmers: a randomized trial. European Journal of Pediatrics. 2011;170:59-63.
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