Vitamin C and the common cold

Abstract

The effect of vitamin C on the common cold has been the subject of several studies. These studies do not support a considerable decrease in the incidence of the common cold with supplemental vitamin C. However, vitamin C has consistently decreased the duration of cold episodes and the severity of symptoms. The benefits that have been observed in different studies show a large variation and, therefore, the clinical significance may not be clearly inferred from them. The biochemical explanation for the benefits may be based on the antioxidant property of vitamin C. In an infection, phagocytic leucocytes become activated and they produce oxidizing compounds which are released from the cell. By reacting with these oxidants, vitamin C may decrease the inflammatory effects caused by them. Scurvy, which is caused by a deficiency in vitamin C, is mostly attributed to the decreased synthesis of collagen. However, vitamin C also participates in several other reactions, such as the destruction of oxidizing substances. The common cold studies indicate that the amounts of vitamin C which safely protect from scurvy may still be too low to provide an efficient rate for other reactions, possibly antioxidant in nature, in infected people.

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

“…For a concise summary of the original results, see ref. 3. The Anderson 1974 study (17) with adults is excluded from Table 1, since there is evidence of biased distribution of subjects in the eight study groups (5,17).…”

“…In placebo-controlled studies, regular vitamin C supplementation ( 1 g/day) has consistently decreased morbidity due to the common cold (1)(2)(3)(4)(5)(6)(7)(8). While the biochemical basis of this effect is not well understood, vitamin C does have diverse effects on the immune system (3,5,9).…”

“…While the biochemical basis of this effect is not well understood, vitamin C does have diverse effects on the immune system (3,5,9).…”

Vitamin C, cholesterol, and the nutritional recommendations

“…1 g/day) ameliorates the symptoms, or shortens the duration, of common cold episodes. 2 Accordingly, the negative conclusions in the RDA monograph are not fully justified.…”

“…Nevertheless, more attention should be given to the findings that the recommended levels are not optimal for sickness prevention or therapy, 1,[12][13][14] and that in certain cases much larger doses may be beneficial. 2 …”