As autumn sets in and the winter approaches, the mind starts to think about the costumes, turkeys, and pine trees, but let’s not forget to plan for a common enemy – the common cold. Many strategies can be taken to keep colds at bay, and they should start with keeping fit and keeping your diet healthy with a focus on fruits and vegetables. One of the most popular nutrients that comes to mind to prevent colds is vitamin C.
Vitamin C is an essential nutrient that is the most important vitamin for antioxidant status. Vitamin C is also beneficial for the maintenance of bones, muscle, and blood vessels. However, even though the connection between vitamin C and colds has been explored for decades, there is still a lot of confusion on the subject. An excellent review has been published which compares the results of 30 studies totaling over 11,000 subjects . The three areas that the review focuses on are incidence of colds, duration, and severity.
Vitamin C & Incidence Of Colds
Incidence of colds is arguably the most important metric, since most people think about the prevention of colds when they are taking a certain supplement for colds. Overall, the review found that vitamin C did not significantly reduce incidence of colds for the general population when the data were pooled. Though some studies reported significant reductions in incidence of colds, many did not see a clear effect. However, when athletes are tested, the results become significant.
Most of the studies that reported significant findings were in athletes: 4 in marathon runners [2-4], one in skiers , and one in soldiers . For example, Peters et al.  investigated the daily consumption of 600 mg of vitamin C and its effect on the development of upper respiratory tract infections after an ultramarathon. In the placebo group, 66% of runners contracted respiratory infections after the race, while only 33% of vitamin C users got sick. In another study by Sabiston and colleagues , 56 men in the same infantry group were provided with supplemental vitamin C in their rations while 56 men were not. All men were undergoing Canadian Northern military operations in subarctic conditions. The benefits on health maintenance were even more profound than in ultramarathoners, with only a 10.7% frequency of colds in vitamin C users, versus a 25% frequency of colds in the non-supplemented group.
Vitamin C & Duration Of Colds
While incidence of colds is the most important outcome for measuring benefit of vitamin C, duration of colds is another useful metric. Even if someone gets the same amount of colds each year, having a cold for a shorter time will improve quality of life and well-being. According to the Douglas meta-analysis , the pooled effect of the 30 studies was a reduction in duration of 8%, which was significant.
For example, Constantin and colleagues  investigated whether 1 gram per day of vitamin C supplementation affected the rate and duration of upper respiratory tract infections (URTI) in adolescent swimmers. Though the incidence was not significantly affected, the duration of URTI was reduced by 22%, especially in males (47%). Severity of URTI was also reduced, but only in males. In another study, Van Straten et al.  followed 168 people through 60 days in winter. The researchers observed that all three parameters were positively affected, wherein vitamin C users reported fewer colds (37 vs. 50), shorter duration of colds (85 vs. 178 days), and less severity (1.8 vs. 3.1 days with severe symptoms per cold).
Vitamin C & Cold Severity
Our third criterion for measurement of benefit of vitamin C on colds is severity, which can be defined in a number of ways. In the 30 studies analyzed from the Douglas study , severity was measured either as days confined to home (out of work or school) or symptom severity scores. Regarding days confined to home, there was a wide range of findings among the studies, but the pooled results were still significant. With symptom severity, there was no way to effectively pool the results because the studies used different scoring methods. As discussed in the Van Straten study  above, many studies have found significant reductions in severity from vitamin C usage. For example, Ludwigsson et al.  performed a pilot study of 172 children and a full study with 643 children and provided 1000 mg of vitamin C daily to the treatment groups. They were followed for 3 months 7 weeks for the pilot), and the treatment group exhibited lower duration of colds and less severity. Similarly, Miller and associates  investigated vitamin C supplementation in 44 school-aged identical twin pairs. Though the findings were mixed, subgroup analysis revealed that duration and severity of colds were reduced for the two youngest groups of girls, and that the youngest group of boys had less severe colds as well.
The Bottom Line On Vitamin C
In conclusion, athletes who train at high intensities and consume vitamin C should expect to see a reduction in the number of colds that they get each year. Additionally, all people will reap the benefits of less severe colds that don’t last as long if vitamin C is consumed daily. Though dosages in studies vary, higher dosages were more likely to elicit benefits, with 1 gram of vitamin C being the most common among the higher doses. Food can be a great source of vitamin C, but to get consistent daily dosing, supplementation is recommended.
- Douglas, R.M., et al., Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev, 2007(3): p. CD000980.
- Peters, E.M., et al., Vitamin C supplementation reduces the incidence of postrace symptoms of upper-respiratory-tract infection in ultramarathon runners. Am J Clin Nutr, 1993. 57(2): p. 170-4.
- Peters, E., et al., Vitamin C as effective as combinations of anti-oxidant nutrients in reducing symptoms of upper respiratory tract infection in ultramarathon runners. S Afr J Sports Med, 1996. 11(3): p. 23-7.
- Himmelstein, S.A., The effect of vitamin C supplementation on incidence of upper respiratory tract infections in marathon runners. 1997.
- Ritzel, G., Letter: Ascorbic acid and the common cold. Vol. 235. 1976. 1108.
- Sabiston, B. and M. Radomski, Health problems and vitamin C in Canadian northern military operations. Defence and Civil Institute of Environmental Medicine Report No. 74-R-M2, 1974.
- Constantini, N.W., et al., The effect of vitamin C on upper respiratory infections in adolescent swimmers: a randomized trial. European journal of pediatrics, 2011. 170(1): p. 59-63.
- Van Straten, M. and P. Josling, Preventing the common cold with a vitamin C supplement: a double-blind, placebo-controlled survey. Advances in therapy, 2002. 19(3): p. 151-159.
- Ludvigsson, J., L.O. Hansson, and G. Tibbling, Vitamin C as a preventive medicine against common colds in children. Scandinavian journal of infectious diseases, 1977. 9(2): p. 91-98.
- Miller, J.Z., et al., Therapeutic effect of vitamin C: A co-twin control study. Jama, 1977. 237(3): p. 248-251.