New York, May 4 (IANS): Overturning a common perception that herbs are safe because they have been used for many years, researchers have warned that long-term use of herbal remedies is no guarantee of their safety as many herbs may contain toxic or carcinogenic substances.

In a commentary published in the journal EMBO reports, researchers from Baylor College of Medicine and Stony Brook University discussed scientific evidence showing that the plant Aristolochia can cause aristolochic acid nephropathy (AAN).

People with this condition experience interstitial nephritis, renal failure and cancers of the urinary track.

In Taiwan, according to the national prescription database, between 1997 and 2003, eight million people were exposed to herbal products containing Aristolochia, the authors remarked.

Studies of patients with renal failure and cancer in Taiwan and China show that tens of millions of people in those countries are at risk of AAN.

In genetically susceptible people, consuming Aristolochia can lead to the formation of complexes between aristolactam, a compound in Aristolachia, and DNA in renal tissues.

These complexes lead to mutations in the TP53 tumour suppressor gene, which in turn initiate the process toward kidney cancer. Additional studies have shown that this process may also lead to the development of cancer in the liver and the bladder, researchers Donald Marcus, professor emeritus at Baylor and Arthur Grollman, distinguished professor of pharmacological sciences at Stony Brook University, explained.

Although Aristolochia has been used as a herbal remedy for more than 2,000 years, "the intrinsic toxicities were not recognised, owing, in large part, to the latency period between exposure and the onset of symptomatic disease, and, in part, to genetic determinants that confer susceptibility to only approximately five percent of those exposed to this herb", said the authors.

The long-term scientific study of AAN revealed the association of the disease with Aristolochia.

"The history of Aristolachia indicates that other herbs that have been used for a long time may also have toxic and/or carcinogenic compounds," said the authors.

"It is prudent to assume that many herbs may contain toxic or carcinogenic substances that can cause subsequent health problems for humans," they noted.

Other herbal products and traditional medicines are responsible for severe adverse events in Africa and Asia, but in these cases epidemiological data are lacking, said the researchers suggesting that herbal remedies may be an overlooked global health hazard.