Overview
In 1986, Professor A. Stewart Truswell of the University of Sydney, Australia concisely summarized the results of 27 trials conducted since 1970. [8] Of these, five were treatment trials with vitamin C or a placebo given only at the onset of a cold and for only several days and all of which found no benefit. The other 22 were double-blind controlled trials giving daily vitamin C or placebo before and during colds. Of these, 12 trials showed no prevention and no reduction in duration or severity, five trials showed no prevention and only slight, statistically nonsignificant lessening of severity, and the other five trials reported no prevention and a small but significant in reduction of duration of the colds. Dr. Truswell concluded: "It is now fairly clear that for preventing colds, vitamin C has no worthwhile effect," but he believed that: "There is thus a little more evidence for a small therapeutic effect of ascorbic acid (vitamin C). However, as Dr. T.W. Anderson's second trial in 1974 revealed 250 mg of vitamin per day reduced severity as much as did 1,000 mg or 4, 000 mg [16].
Does it make sense to supplement with vitamin C? If so, should it be done daily or only at the first sign of a cold or other infection? And what dosage should be used? The many studies done in the last 30 years clearly prove that daily vitamin C supplements, whether 100 mg or 5,000 mg, do not prevent colds and provide, but only for some people, only a slight reduction in duration and severity of colds. Dr. Thomas Chalmers concluded in 1975: "I, who have colds as often and as severe as those of any man, do not consider the very minor potential benefit that might result from taking vitamin C three tines a day for life worth either the effort or the risk, no matter how slight the latter might be." [5]
If you choose to supplement when a cold strikes, there is no reason to take more than 250 mg per day, as shown in the 1974 Anderson study. This amount is easily obtained from the age-old "remedy," fruit juices. Supplementation with larger amounts of vitamin C has not been shown to be more effective, and it may cause diarrhea or have other adverse effects.