Fans of echinacea have long sworn that it can ward off the common cold, a claim that has been dismissed this as a matter of faith. Now scientists say that the herbal remedy really works, giving believers the pleasure of watching the cynics swallow their words. An analysis of the evidence has found that taking the remedy more than halves a person’s chances of catching a cold and shortens the length of a cold by an average of 1.4 days.

The American team reviewed 14 studies and published their results in Lancet Infectious Diseases. But some earlier studies failed to find convincing evidence that echinacea worked, so the findings are likely to be controversial.

Ron Cutler, of the School of Biosciences at the University of East London, said: “Echinacea has traditionally been used for both prevention and treatment of colds but recent studies suggest that it may be more effective as a treatment.

“It may reduce the duration of illness and decrease the severity of cough, headache, and nasal congestion. People with impaired immune function may benefit from taking echinacea during the winter months to prevent colds and flu, but healthy people do not require long-term preventative use.”

Ronald Eccles, director of the Common Cold Centre at the University of Cardiff, said that it was a significant step in the battle against the common cold. He added: “Harnessing the power of our own immune system to fight common infections with herbal medicines is now given more validity with this interesting scientific evaluation of past clinical trials.”

The research team, led by Craig Coleman of the School of Pharmacy at the University of Connecticut, searched the medical literature for studies on echinacea and found 14 previous reports that met their criteria. When the results were pooled they found that taking echinacea reduced the chances of catching a cold by 58 per cent.

It was more effective in natural circumstances, where colds were caught in the normal way, than it was in trials in which volunteers were innoculated directly with the common cold rhinovirus. “With over 200 viruses capable of causing the common cold, echinacea could have modest effects against rhinovirus but marked effects against other viruses,” they say.

One trial combined echinacea with vitamin C, and that reduced colds by 86 per cent. But as only one trial used this particular combination, the authors could not be certain of the finding. The combined trials also produced evidence that echinacea reduced the duration of a cold by an average of 1.4 days. All the studies showed a reduction, but the amount varied from more than three days to less than one.

The authors caution that more work needs to be done on the safety of echinacea, which was not covered in the review.

They concluded: “An analysis of the current evidence in the literature suggests that echinacea has a benefit in decreasing the incidence and duration of the common cold.

However, 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.”

Professor Cutler added: “Overall this study, although well structured, only produces a small increase in our understanding. The true benefits and, more importantly, how the agents work, remain unclear.”

Flower power

— Echinacea is a collection of nine related plant species indigenous to North America and is one of the most commonly used of herbal supplements

— Echinacea angustifolia, Echinacea pallida and Echinacea purpurea are most commonly used in such supplements, but how they work is unclear

— All three species contain the same constituents in differing concentrations. It is thought that three of these (alkamides, chicoric acid, polysaccharides) may stimulate immune systems

— The review found more than 800 products containing echinacea

Source: Times database

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