Millions of people may be exposed to risk of developing kidney failure and bladder cancer by taking herbal medicines that are widely available in Asia, scientists from King`s College London have warned.

The medicines, used for a wide range of conditions including slimming, asthma and arthritis, are derived from a botanical compound containing aristolochic acids.

These products are now banned in the USA and many European countries but the herbs containing this toxic acid can still be bought in China and other countries in Asia and are also available worldwide over the internet.

The scientists reviewed worldwide cases of aristolochic acid nephropathy (AAN) - a type of kidney failure caused by the intake of these acids.

They explained the clinical basis for the disease and propose strategies to help doctors identify it and treat patients more effectively.

They suggested that there might be many thousands of cases across Asia that are undiagnosed or misdiagnosed. With the outcome of their study, the researchers hope to raise awareness of the risks of aristolochic acids and reduce the global disease burden from this severe condition.

"We have found evidence that many millions of people continue to be exposed to significant health risk due to these herbal medicines, widely used in China and India," said lead author Professor Graham Lord, Director of the National Institute for Health Research (NIHR) Biomedical Research Centre (BRC) at Guy`s and St Thomas` NHS Foundation Trust and King`s College London.

The paper indicates that regulatory measures that have so far been adopted by national and international agencies may be inadequate in preventing harmful exposure to aristolochic acid. The compound is linked to many cases of kidney diseases and urothelial cancer, a form of cancer of which bladder cancer is the most known variant.

The researchers reviewed the latest data on the epidemiology of AAN. They used several search engines to include all publications that are about or refer to aristolochic acid and Chinese herbal nephropathy and identified 42 different case studies and one trial relating to the management of the disease.

While explaining the origin and development of the disease, they propose a protocol that should make it easier to diagnose AAN. In addition, they suggested a new disease classification to help international clinicians better identify AAN patients, and draft guidelines for the treatment of these patients.

The research was published in Annals of Internal Medicine.