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LONDON (Reuters) - Herbal medicines are popular among asthma sufferers but researchers said on Tuesday there was very little medical evidence that they work.

Two-thirds of people with mild asthma and three-quarters of sufferers with severe cases use complementary remedies to control the illness or relieve wheezing and breathlessness caused by the illness, according to a survey by the National Asthma Campaign in England.

Traditional Chinese medicine, Ayurvedic or Indian treatments, ginkgo biloba and Japanese herbal therapies are among the complementary treatments for the illness that afflicts about 150 million people worldwide.

But Dr. Alyson Huntley, of the department of complementary Medicine at the University of Exeter, said a review of 17 published studies into the effectiveness of herbal treatments showed the research was inconclusive.

"We just don't know if they work," Huntley said in a telephone interview. "At the moment there is no conclusive evidence."

Many of the studies were either flawed or did not use products of standardized quality so it was difficult to know how effective they were.

"Although some trials yield positive results, their flaws mean that further meticulous investigations are required before positive recommendations can be made," Huntley said in a report in the journal Thorax.

Many of the herbal medicines reviewed in the research could have adverse effects or interact badly with prescribed drugs so there are still are also uncertainties about their safety.

"It is concluded that herbal medicinal products, even though in prevalent use, are of uncertain value in the treatment of asthma," Huntley added.

She stressed the need for urgent, stringently designed studies because of the popularity of the treatments with asthma sufferers.

Asthma is one of the most common chronic diseases and is increasing at an alarming rate. The number of cases of the disease, which affects the small tubes that carry air in and out of the lungs, has risen significantly in developed countries in the last 25 years.

Scientists suspect that sterile modern lifestyles are contributing to the increase in cases. There is no cure, but drugs can relieve many of the symptoms.

Last modified: March 30, 2007