Vitamin C supplementation and common cold symptoms: factors affecting the magnitude of the benefit

Abstract

SUMMARYPlacebo-controlled trials have shown that vitamin C supplementation decreases the duration and severity of common cold infections. However, the magnitude of the benefit has substantially varied, hampering conclusions about the clinical significance of the vitamin. In this paper, 23 studies with regular vitamin C supplementation ( 1 g/day) were analyzed to find out factors that may explain some part of the variation in the results. It was found that on average, vitamin C produces greater benefit for children than for adults. The dose may also affect the magnitude of the benefit, there being on average greater benefit from 2 g/day compared to 1 g/day of the vitamin. In five studies with adults administered 1 g/day of vitamin C, the median decrease in cold duration was only 6%, whereas in two studies with children administered 2 g/day the median decrease was four times higher, 26%. The trials analyzed in this work used regular vitamin C supplementation, but it is conceivable that therapeutic supplementation starting early at the onset of the cold episode could produce comparable benefits. Since few trials have examined the effects of therapeutic supplementation and their results have been variable, further therapeutic trials are required to examine the role of vitamin C in the treatment of colds.

Commentaries on ‘Vitamin C for preventing and treating the common cold’ with responses from the review author

“…In five trials with adults who were administered 1 g/day of vitamin C, the mean decrease in cold duration was only 7%, whereas in two trials with children administered 2 g/day the mean decrease was four times higher, 26% (32)(33)(34). Children administered 1 g/day and adults administered ≥ 2 g/day were in the middle with mean effects of 13% and 20%, respectively.…”

“…However, each scientific report is a compromise between the length and details, and our Cochrane review is already long for an average reader (1). Not all specifics could be discussed, yet the dose-response question was briefly commented on, with the reader being guided to a separate systematic review (32).…”

“…In 1999, I divided the vitamin C common cold trials simultaneously by dose: 1 g/day vs. ≥ 2 g/day regularly over the trial, and by participants: children vs. adults (32). A major challenge in the analysis was choosing an appropriate outcome.…”

“…In the 1999 analysis, when several outcomes were published in a trial report, I selected the outcomes seemingly most important for the patient, such as days off work or school (32), which made the outcomes more relevant but more heterogeneous. In five trials with adults who were administered 1 g/day of vitamin C, the mean decrease in cold duration was only 7%, whereas in two trials with children administered 2 g/day the mean decrease was four times higher, 26% (32)(33)(34).…”

Regular vitamin C supplementation during pregnancy reduces hospitalization: outcomes of a Ugandan rural cohort study

“…The book highlights the benefit in decreasing the incidence of common cold by a continuous and mega-dose vitamin C intake (>1g/day). Several randomized placebo controlled studies have attempted to repeat Pauling's experience with inconsistent and variable results which to date can not provide a definite conclusion around the real extent of overall health benefit brought in by vitamin C high daily intake [16][17][18].…”