Volume 176 - Issue 5
Megadose vitamin C in treatment of the common cold: a randomised controlled trial
Authors: Luis Vitetta, Avni Sali, Bill Paspaliaris and Nicola J Reavley
Med J Aust 2002; 176 (5): 298-299. || doi: 10.5694/j.1326-5377.2002.tb04393.x
Published online: 4 March 2002
Published online: 4 March 2002
To the Editor: There is much conflicting evidence that increased intake of vitamin C enhances the natural protective mechanisms of the body and decreases both the incidence and severity of the common cold.1
It is regrettable that the study by Audera and colleagues failed to show a significant therapeutic effect of megadose vitamin C in treatment of the common cold.2 The groups compared had, on average, similar composition after randomisation. However, the viral infections that cause the common cold and its progression to ill health, as evidenced by multiple symptoms, are affected by many factors, while symptom severity is well known to vary greatly. Therefore, the study's reliance on respondents' self-diagnosis of symptom severity and onset is a significant weakness in design.
Randomisation of participants to the treatment groups may have been insufficient to override this design deficit, thereby significantly biasing the outcome. A better design might have combined patient self-report of symptom severity with physical examination, thus allowing independent and professional assessment of severity. Also, proper assessment of previous history of severity of cold symptoms is crucial for proper randomisation to treatment groups. If Audera and colleagues' study failed to control for this history, then randomisation may have also failed to balance its effect equally between treatment groups, significantly compromising the study's validity to detect any therapeutic benefit of vitamin C. Cold symptoms also vary diurnally, while severity varies with alcohol use and smoking status,3,4 which also affect vitamin C absorption.5,6 No information was provided on study participants' alcohol consumption and smoking status.
Finally, the study did not assess stress, which may constitute a further, important uncontrolled bias. A recent cohort study of stress and the common cold concluded that all four dimensions of stress investigated — stressful life events, negative affects, positive affects and perceived stress — were significantly related to occurrence of the common cold.7 Stress may also have significantly affected symptom severity and participants' perception of their symptoms.
Certainly, the trend observed in the placebo group of shorter duration of some symptoms and lower mean severity could have been due to less severe symptom history, compounded by a lower degree of overall stress.
References
- Douglas RM, Chalker EB, Treacy B. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev 2000; 2: CD000980. CBBBJFIG
- Audera C, Patulny RV, Sander BH, Douglas RM. Mega-dose vitamin C in treatment of the common cold: a randomised controlled trial. Med J Aust 2001; 175: 359-362. <eMJA full text>
- Smith A, Tyrrell D, Coyle K, et al. Diurnal variation in the symptoms of colds and influenza. Chronobiol Int 1988; 5: 411-416. i1146960
- Cohen S, Tyrrell DA, Russell MA, et al. Smoking, alcohol consumption, and susceptibility to the common cold. Am J Public Health 1993; 83: 1277-1283. i1146962
- Pamuk E, Byers T, Coates R, et al. Effect of smoking on serum nutrient concentrations in African–American women. Am J Clin Nutr 1994; 59: 891-895. i1146965
- Kleszczewski T, Kleszczewska E. FIA of vitamin C in blood serum in humans at increasing ethanol concentration. J Pharm Biomed Anal 2001; 25: 477-481. i1146967
- Takkouche B, Regueira C, Gestal-Otero JJ. A cohort study of stress and the common cold. Epidemiology 2001; 12: 345-349. i1146969
- Audera C, Patulny RV, Sander BH, Douglas RM. Mega-dose vitamin C in treatment of the common cold: a randomised controlled trial. Med J Aust 2001; 175: 359-362. <eMJA full text>
- Tyrrell DJ, Craig JW, Meade TW, White TA. A trial of ascorbic acid in the treatment of the common cold. Br J Prev Soc Med 1977; 31: 189-191.
- Douglas RM, Chalker EB, Treacy B. Vitamin C for preventing and treating the common cold (Cochrane Review). In: The Cochrane Library 3, 2001. Oxford: Update Software. i1146952