June 26, 2007 -- Taking the herbal supplement echinacea can cut your chances of catching a cold by more than half and shorten the duration of a cold by an average of 1.4 days, a new review of the research shows.
Researchers from the University of Connecticut combined findings from 14 previously reported trials examining echinacea to prevent or treat the common cold.
While many of the most rigorous trials failed to show a significant benefit for the supplement when reported alone, the combined trial analysis showed a much stronger benefit, the researchers say.
Use of the herbal supplement was found to reduce the risk of catching a cold by 58%, while the combination of echinacea and vitamin C reduced cold incidence by 86% in one study.
But a longtime critic of the study of echinacea as a cold remedy remains unconvinced by the new analysis.
Wallace Sampson, MD, who edits the Scientific Review of Alternative Medicine, tells WebMD that the reviewed studies were too different to provide meaningful results when pooled together.
“If you have studies that measure different things, there is no way to correct for that,” the Stanford University emeritus clinical professor of medicine says. “These researchers tried, but you just can’t do it.”
Echinacea and the Common Cold
Echinacea, a collection of nine related plant species found in North America, is the most widely used herbal supplement in North America. More than 800 products contain some form of the herbal in the U.S., according to the University of Connecticut researchers.
While more than 70 studies examining the use of echinacea for colds were identified, C. Michael White, PharmD, tells WebMD that only the highest-quality trials were included in the analysis.
In studies that involved volunteers being directly inoculated with a cold-causing virus -- considered the most rigorous trial design -- use of echinacea was found to reduce cold incidence by 35%.
White says the reduced effectiveness in these trials may mean that echinacea is better for preventing natural virus exposure than exposure to the single rhinovirus used in the trials.
More than 200 individual viruses are known to be capable of causing the common cold.
The analysis is published in the July issue of the journal Lancet Infectious Diseases.
“When you combine the best studies they support the conclusion that echinacea reduces the risk of catching a cold and reduces the duration of colds,” White says. “What we don’t know is whether or not long-term exposure to echinacea is safe.”
Safety of Echinacea for Colds Unknown
None of the studies analyzed by White and colleagues included long-term safety data on the use of echinacea for the prevention and treatment of colds.
The researchers write that larger trials evaluating safety are needed, “before echinacea for the prevention or treatment of the common cold can become standard practice.”
This is especially true for people who are already in poor health or are taking many other drugs, White says.
“If someone has multiple health conditions or is on multiple medications, they should be careful about taking any herbal product,” he says.
Sampson contends the use of echinacea as a cold remedy has more to do with aggressive marketing than sound science.
He dates its modern-day use for this purpose to a Swiss herbal supplement maker who, during a trip to South Dakota in the 1960s, was erroneously told echinacea was used for cold prevention by Native American tribes who lived in the area.
“There is no more reason to study echinacea to prevent colds than there is to study echinacea to prevent auto accidents,” Sampson says.