US researchers who reviewed over a dozen studies on the effect of echinacea have concluded that the popular herbal remedy reduces a person’s chance of catching a cold by 58 per cent. And they found that it also cuts the duration of a cold by an average of 1.4 days.
The study is published in the July edition of The Lancet Infectious Diseases.
The researchers were led by Dr Craig Coleman from the University of Connecticut School of Pharmacy, Hartford Hospital, Connecticut.
Echinacea is one of the most popular and frequently used herbal remedies but scientific and medical opinion about its effect on the common cold is controversial.
Coleman and colleagues decided to review the current literature using an approach called a “meta-analysis” which pools the results of previous trials and examines them using a rigorous set of statistical methods. Their analyses reviewed 14 trials that studied the effect of echinacea on prevention and treatment of the common cold.
Using a method that calculates the Odds Ratio of incidence of the common cold in the pooled participants, the researchers found that echinacea decreased the odds by 58 per cent (the statistically significant odds ratio was 0.42 with a 95 per cent confidence interval ranging from 0.25 to 0.71).
They also found by using a random effects statistical model that the effect of echinacea was to reduce the duration of a cold by 1.4 days (the statistically significant weighted mean difference was -1.44 with a 95 per cent confidence interval ranging from -2.24 to -0.64).
Only one of the studies they reviewed looked at a echinacea in combination with vitamin C. This reported a reduction in cold incidence of 86 per cent for the combined dose. Because there was only one study in this category the authors felt they were not able to say with confidence whether the two supplements were better than echinacea alone at fighting off colds.
The studies they reviewed took into account two ways of testing against the common cold. One way was to allow the participants to catch a cold “naturally” and see how effective echinacea was at this. The other way was to inject participants with rhinovirus, one of the many viruses that causes the common cold.
Echinacea reduced cold incidence by 65 per cent when it was used as a protective against catching it naturally. It still gave protection against the injected rhinovirus but this was only at 35 per cent. The researchers said that:
“With over 200 viruses capable of causing the common cold, echinacea could have modest effect against rhinovirus but marked effects against other viruses.”
Echinacea is a family of nine plant species indigenous to North America and is the most commonly used herbal product or “nutraceutical”, a term used to describe food supplements used as medicines.
The types of echinacea that are most commonly used for medicinal purposes are Echinacea angustifolia, Echinacea pallida, and Echinacea purpurea.
The study found over 800 products containing echinacea are sold as supplements, and all parts of the plant are used: flower, stem and root. All three of the popular medicinal species contain the same chemical constituents but in different proportions.
It is thought likely that the alkamides, chicoric acid and polysaccharides in the echinacea plant stimulate the immune system but scientists are not sure how: do they work singly or in combination with each other and perhaps other unknown chemicals in the plant?
The researchers concluded that:
“Published evidence supports echinacea’s benefit in decreasing the incidence and duration of the common cold.”
However, they said that more research is needed to find out how safe echinacea is and to discover exactly what it does in the body.
“Large-scale randomised prospective studies controlling for variables such as species, quality of preparation and dose of echinacea, method of cold induction, and objectivity of end points evaluated are needed before echinacea for the prevention or treatment of the common cold can become standard practice,” explained Coleman and colleagues.
If you are on medication and considering taking echinacea, speak to your doctor first. A study last year concluded that echinacea can sometimes interfere with drug treatment by moving it out of the body too fast. Click here to read about that study.
“Evaluation of echinacea for the prevention and treatment of the common cold: a meta-analysis.”
The Lancet Infectious Diseases 2007; 7:473-480
DOI:10.1016/S1473-3099(07)70160-3
Sachin A Shah, Stephen Sander, C Michael White, Mike Rinaldi, and Craig I Coleman.
Written by: Catharine Paddock
Writer: Medical News Today