The age-old wisdom that vitamin C can help reduce the incidence of colds recently had another setback in a study from Finland, published in Cochrane Database of Systemic Reviews at the end of January 2013.
A review of placebo-controlled trials looking at vitamin C and colds carried out since 1966 showed that while vitamin C does have a small, consistent effect on the duration of colds, there was no effect on the incidence. The only exception was in patients who had been exposed to short periods of extreme physical stress.
The study seems to put an end to the debate over vitamin C’s ability to reduce the number of colds that someone has. The researchers excluded any study that used a vitamin C daily dosage of less than 0.2 g.
According to researchers, the studies looking at the incidence of colds in community populations had a pooled risk ratio (RR) of 0.97 (95% CI; 0.94–1.00), which represents an insignificant risk reduction of 3%. In studies surveying subjects involved in extreme activities such as running a marathon, the RR was 0.48 (95% CI; 0.35–0.64), showing a statistically significant risk reduction of 52%.
Data from 31 studies focused on whether or not vitamin C reduced the length of colds and demonstrated that regular supplements helped reduce symptoms by 8% in adults and 14% in children. However, data from seven studies concerning therapeutic supplementation started after the beginning of a cold indicated no consistent effects on either duration or severity of the cold.
“Given the consistent effect of vitamin C on the duration and severity of colds in the regular supplementation studies, and the low cost and safety, it may be worthwhile for common cold patients to test on an individual basis whether therapeutic vitamin C is beneficial for them,” the authors stated.