Echinacea may not only help reduce the symptoms of a cold but may help prevent infection with some cold viruses, U.S. researchers said on Monday.
People who took echinacea had a 58 percent lower risk of catching a cold, according to the researchers, who did not study the herb's effects directly but looked at the results of 14 studies in an approach called a meta-analysis.
Dr. Craig Coleman of the University of Connecticut School of Pharmacy, who led the research, cautioned that the studies only involved 1,600 people. They also involved various echinacea products, so it was still difficult to know for sure if and how echinacea might work to prevent colds.
"All the studies trended toward reducing a patient's odds of developing a cold. But none of them was large enough — they didn't have enough patients — to prove it statistically," said Coleman in a telephone interview.
Coleman's study, published in the journal Lancet Infectious Diseases, is one of the few to take a look at the efficacy of echinacea, a widely used product derived from several different species of flower.
"Someone needs to do a really large, well-done, randomized trial. That is unlikely to occur because there is a lack of funding," Coleman said.
Drug companies cannot patent such a widely used herbal product, he noted.
In 2005, a study published in the New England Journal of Medicine found echinacea was of no benefit in stopping colds. Coleman said it only looked at part of the picture.
"In that study what they did was they took healthy volunteers and they inoculated them, put a little Q-tip (cotton swab) up their nose. The problem is there are more than 200 kinds of viruses that cause colds," Coleman said.
The team that did this particular study only looked at a rhinovirus.
"So maybe it doesn't work against that kind of virus, but it does against the other 199 kinds."
Coleman said it also appeared as if echinacea reduced the duration of a cold by 1.4 days on average.
One of the studies looked at echinacea used together with with vitamin C, another common cold remedy, and that one showed the two together reduced the number of colds by 86 percent.
The term echinacea refers to parts taken from nine related plant species indigenous to North America. It was used originally by Native Americans and is now the most commonly used "nutraceutical" product — a catchall term that refers to herbs and some supplemented foods.
Coleman, a pharmacist, said it appears to stimulate the immune system, although no one quite knows how it works.
It might also cause harmful effects, he said.
"While echinacea is generally regarded as safe, it hasn't undergone any long-term safety evaluation," Coleman said.
"So you should use it with caution."
Patients with autoimmune diseases such as lupus and multiple sclerosis should be particularly careful, he said. In addition, echinacea affects a liver enzyme that breaks down some drugs, so using it with prescription medications could cause drug interactions.