Vitamin C was identified in the early part of the previous century and there was much interest in its possible effects on various infections including the common cold. A few controlled trials on the effect of vitamin C on the common cold were carried out already in the 1940s, but the topic became particularly popular after 1970, when Linus Pauling, a double Nobel laureate, wrote a best-selling bookVitamin C and the Common Cold. Pauling's book led to great interest in the topic among lay people, but also among academic circles. After Pauling's book, a number of controlled trials were carried out. However, the interest disappeared after the middle of 1970s apparently because of the publication of two reviews and one primary study, which all concluded that vitamin C does not influence the common cold. However, the three papers were later shown to be erroneous. According to the Cochrane review on vitamin C and the common cold, 1 g/day or more of vitamin C does not influence common cold incidence in the general community. However, in five randomized double-blind placebo-controlled trials with participants who were under heavy short-term physical stress, vitamin C halved the incidence of colds. In the dose of 1 g/day or more, vitamin C shortened the duration of colds in adults by 8% and in children by 18%. Vitamin C also decreased the severity of colds.
Echinacea
A systematic review by the Cochrane Collaboration, last updated in 2014, examines twenty-four randomized controlled trials studying various echinacea preparations for prevention and treatment of the common cold. Echinacea showed no benefit over placebo for prevention. Evidence for treatment was inconsistent. Reported side effects were rare. 2007 meta-analyses conclude that there is some evidence that echinacea may reduce either the duration or severity of the common cold, but results are not consistent. Use of echinacea preparations is not currently recommended.
Chicken soup
In the twelfth century, Moses Maimonides wrote, "Chicken soup... is recommended as an excellent food as well as medication." Since then, there have been numerous reports in the United States that chicken soup alleviates the symptoms of the common cold. Even usually staid medical journals have published tongue-in-cheek articles on the alleged medicinal properties of chicken soup.
''Pelargonium sidoides'' extract
A 2013 Cochrane review found tentative evidence of benefit with Pelargonium sidoides for the symptoms of the common cold; however, the quality of the evidence was very poor.
Steam inhalation
Many people believe that steam inhalation reduces cold symptoms. There is no evidence suggesting that steam inhalation is effective for treating the common cold. There have been reports of children being badly burned by accidentally spilling the water used for steam inhalation. Evidence does not support a relationship between cold temperature exposure or a "chill" and the common cold.
Zinc
Zinc is tentatively linked to a shorter length of symptoms.
