Synopsis

Source of validity: Scientific
Rating (out of 5): 2

Citrus spp. (such as oranges, lemons, and grapefruits) are widely used to support or prevent colds, primarily due to their high vitamin C (ascorbic acid) content. The tradition of using citrus fruits for colds dates back to the early 20th century, but scientific investigation into the efficacy of vitamin C supplementation for cold prevention began in earnest in the latter half of the 20th century. The most comprehensive analyses, such as Cochrane reviews, indicate that regular vitamin C supplementation (at doses of 200 mg or more per day) does not significantly reduce the incidence of colds in the general population but may slightly reduce the duration and severity of cold symptoms. There is some modest evidence that people under severe physical stress (e.g., marathon runners) may experience a reduction in cold incidence with vitamin C supplementation. However, consuming citrus fruits as part of a normal diet is unlikely to provide a therapeutic dose of vitamin C sufficient to have these effects. Overall, while the use of citrus spp. for cold prevention is supported by a combination of tradition and some scientific evidence, the strength of the scientific evidence is moderate to low, and the clinical impact is limited.

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